Bryant Thermostat Q674 User manual

PRODUCT DATA

60- 248

5

-

8

® U.S. Re

g

istered Trademark

Cop

y

ri

g

y

well • All Ri

g

hts Reserved

T874 Multistage Thermostats

and Q674 Subbases

APPLICATION

These thermostats and subbases provide low volta

g

e control

of multista

g

e heatin

g

and coolin

g

s

y

stems, includin

g

heat

pump s

y

stems.

FEATURES

• T874 Thermostat has silent, dust-free mercury

switches operated by coiled bimetal elements.

• Heat anticipator(s) are adjustable or fixed cooling

anticipator(s) are fixed.

• Individual heat and cool levers and scales (most

models) for temperature setting located on top of

thermostat case.

• Cover thermometer on most T874 Multistage

Thermostat models.

• Locking cover and locking lever screws available for

T874 Multistage Thermostats.

• Versaguard™ Thermostat Guard or custom key lock

thermostat guards available for T874 Multistage

Thermostats.

• T874 Thermostat requires a Q674 Subbase.

• Q674 Subbase provides system and fan switching,

wiring terminals and mounting base for T874

Multistage Thermostat.

• Adapter plate available for mounting Q674 on wall or

horizontal outlet box.

• Light-emitting diodes (LEDs) located on subbase for

easy reference.

• Up to three stages each of heating and cooling control

possible.

• Models with setpoint restrictions and locking cover

with no thermometer available for Department of

Defense (DoD) and other special applications.

• Outdoor reset used on some models to improve

thermal performance.

Contents

Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Ordering Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Checkout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Understanding Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Cross Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Wiring Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

60-2485—82

ORDERING INFORMATION

When purchasin

g

replacement and modernization products from

y

our TRADELINE® wholesaler or distributor, refer to the

TRADELINE® Catalo

g

or price sheets for complete orderin

g

number.

If

y

ou have additional

q

uestions, need further information, or would like to comment on our products or services, please write or

phone:

1.

Your local Home and Buildin

g

Control Sales Office

(

check white pa

g

es of

y

our phone director

y)

.

2.

Home and Buildin

g

Control Customer Relations

Hone

y

well, 1885 Dou

g

las Drive North

Minneapolis, Minnesota 55422-4386

(

800

)

328-5111

In Canada—Hone

y

well Limited/Hone

y

well Limitée, 35 D

y

namic Drive, Scarborou

g

h, Ontario M1V 4Z9.

International Sales and Service Offices in all principal cities of the world. Manufacturin

g

in Australia, Canada, Finland, France,

German

y

, Japan, Mexico, Netherlands, Spain, Taiwan, United Kin

g

dom, U.S.A.

SPECIFICATIONS

IMPORTANT

The specifications given in this publication do not

include normal manufacturing tolerances. Therefore,

this unit may not exactly match the listed specifica-

tions. This product is tested and calibrated under

closely controlled conditions, and some minor differ-

ences in performance can be expected if those con-

ditions are changed.

Super Tradeline

®

/Tradeline

®

Models

SUPER TRADELINE controls offer features not available on

TRADELINE or standard models, and are desi

g

ned to replace

a wide ran

g

e of Hone

y

well and competitive controls.

TRADELINE models are selected and packa

g

ed to provide

ease of stockin

g

, ease of handlin

g

, and maximum

replacement value. Specifications of SUPER TRADELINE

and TRADELINE controls are the same as those of standard

models except as noted below.

Super Tradeline Models

T874 THERMOSTAT

T874D Thermostat. Provides two sta

g

es of heatin

g

and two

sta

g

es of coolin

g

. Use with Q674A-F Subbases.

Y594D

(

T874D/Q674E/TG504A

)

Thermostat/Subbase/ke

y

lock cover packa

g

e. Provides two sta

g

es of heatin

g

and

two sta

g

es of coolin

g

. Includes a ke

y

lock cover for set-

point protection.

Y594G

(

T874G/Q674F

)

Thermostat/Subbase packa

g

e for

heat pump. Provides two sta

g

es of heatin

g

and one sta

g

e

of coolin

g

. Automatic chan

g

eover in heat or cool mode.

Available in bei

g

e or Premier White® color.

Y594R

(

T874R/Q674L

)

Thermostat/Subbase packa

g

e for

heat pump. Provides two sta

g

es of heatin

g

and one sta

g

e

of coolin

g

. Manual chan

g

eover in heat or cool mode. Avail-

able in bei

g

e or Premier White® color.

SUPER TRADELINE FEATURES:

• SUPER TRADELINE packa

g

e with cross reference label

and special instruction sheet.

• SUPER TRADELINE model supplied with lockin

g

lever and

lockin

g

cover accessories.

• Includes ad

j

ustable temperature lockin

g

stops.

• T874D replaces T874A-F TRADELINE or standard models.

Tradeline Models

T874 THERMOSTAT

• T874 TRADELINE models provide sta

g

ed heat and/or cool

operation. See Table 1.

Table 1. Heating and Cooling Stages.

• T874A-F are standard models.

TRADELINE FEATURES:

• TRADELINE packa

g

e with cross reference label and

special instruction sheet.

• T874A,C model available with factor

y

stops for DoD

applications.

• T874A,C model available with ad

j

ustable temperature

lockin

g

stops.

Q674 SUBBASE

Q674 switchin

g

subbases provide s

y

stem and fan switchin

g

.

See Table 2.

Table 2. System and Fan Switching.

TRADELINE FEATURE:

• TRADELINE packa

g

e with cross reference label and

special instruction sheet.

• Q674A-E,G are standard

(

non-heat pump

)

models.

Q674F,J,L are heat pump models.

Models ABCDEF

Heatin

g

Sta

g

es 1122— 2

Coolin

g

Sta

g

es 12122—

Q674 System Fan

A Heat-Auto-Cool Auto-On

B Heat-Off-Cool Auto-On

C Off-Auto Auto-On

D None None

E Off-Heat-Auto-Cool Auto-On

F Em. Ht.-Off-Heat-Auto-Cool Auto-On

G Off-Auto None

J Em. Ht.-Auto-Off Auto-On

L Em. Ht.-Heat-Off-Cool Auto-On

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

3 60-2485—8

Standard Models

T874 THERMOSTATS

Models:

See Table 3.

Electrical Rating:

24 to 30 Vac.

Switching:

Coiled bimetal elements operate mercur

y

switches.

Temperature Adjustment:

Heatin

g

and coolin

g

settin

g

levers, with separate scales located on top of thermostat

base. Common lever for heatin

g

and coolin

g

on T874R;

one coolin

g

lever on T874E,V; and one heatin

g

lever on

T874F,Q.

Dimensions:

See Fi

g

. 1.

Temperature:

Scale Ran

g

e: 42° to 88°F

(

6° to 31°C

)

stan-

dard; optional ran

g

es available.

Thermometer Range:

42° to 88°F

(

6 to 31°C

)

Changeover Differential:

4°F

(

2°C

)

minimum between heat-

in

g

and coolin

g

(

5°F [3°C] on T874W

)

. Levers can be set

apart for

g

reater separation.

Interstage Differential:

Standard Models: Mechanical differential is 1°F

(

0.6°C

)

between heatin

g

or coolin

g

sta

g

es; operatin

g

differential is

approximatel

y

1.9°F

(

1°C

)

between sta

g

es in heatin

g

or

coolin

g

.

Special Models: See Table 3.

Finish:

Bei

g

e or Premier White

®

finish.

Mounting Means:

T874 Multista

g

e Thermostat mounts on

Q674 Subbase. Subbase mounts horizontall

y

on wall or

outlet box. Mounts on vertical outlet box with optional

193121A Adapter Plate Assembl

y

.

Fig. 1. T874 Thermostat and Q674 Subbase dimensions in in. (mm).

Optional Specifications (T874 Only):

Temperature scale ran

g

es are 40° to 75°F

(

4° to 24°C

)

heat-

in

g

and 75° to 90°F

(

24° to 32°C

)

coolin

g

with stop; 44° to

68°F

(

7° to 20°C

)

heatin

g

, 80° to 86°F

(

27° to 30°C

)

cool-

in

g

; 6° to 29°C

(

43° to 85°F

)

Celsius scale; 3° to 22°C

(

38°

to 72°F

)

and 26° to 32°C

(

78° to 90°F

)

coolin

g

with stop.

Nonad

j

ustable factor

y

-added stop limits heatin

g

setpoint to

72°F

(

22°C

)

maximum and coolin

g

setpoint to 78°F

(

26°C

)

minimum.

OEM customer personalization.

Lockin

g

cover and lockin

g

lever

(

see Thermostat Accesso-

ries

)

.

Thermostat cover without thermometer.

Ad

j

ustable lockin

g

temperature stops.

Volta

g

e heat anticipation for first or second sta

g

e heat or both.

See Table 3.

Fast c

y

clin

g

on heatin

g

sta

g

e

(

s

)

for electric heat applications.

C815A Outdoor Thermistor for improved performance on

specified models.

Thermostat Accessories:

Lockin

g

Cover and Lockin

g

Lever Assembl

y

: Part no.

194559R with thermometer; 194559S without thermome-

ter. See Fi

g

. 2. Includes cover, screws, and Allen wrench

for lockin

g

cover. The screws must be used to assure

proper operation.

Ad

j

ustable Lever Stop: Part no. 4074ECK; includes lever stop

and screws.

Universal Versa

g

uard™ Thermostat Guard: Includes wall-

plate, rin

g

base,

g

uard cover, tumbler lock, two ke

y

s and

optional Hone

y

well lo

g

o insert. Double-wall construction

provides extra measure of tamper-resistance. Tamper-

resistant lock; ke

y

cannot be removed without bein

g

in

locked position. Vents in

g

uard base allow airflow for opti-

mum thermostat performance. See form 68-0104 for more

information.

— TG511A1000: Clear cover.

— TG511B1008: Opa

q

ue cover.

— TG511D1004: Painted steel

(

off-white

)

cover. See

Fi

g

. 2.

M5849

FAN

AUTO ON

OFF

EM. HT. HEAT AUTO COOL

(38)

(87)

SUBBASE

THERMOSTAT MOUNTED

ON SUBBASE

SIDE

50 60 70 80

HEAT COOL

FAN

AUTO ON

OFF

EM. HT. HEAT AUTO COOL

(89)

FRONT

2-3/16 (56)

1-7/8 (48)

3-1/2

5-1/8 (130)

1-1/2

3-9/32 (83)

3-7/16

3/8 (10)

5-5/8 (143)

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

60-2485—84

Ke

y

Lock Cover: Part no. TG504A replaces existin

g

T874

cover. Mounts on T874 base and covers thermostat set-

tlin

g

levers and subbase switches. Includes LED window

and two ke

y

s. Should not be used with 193121A Adapter

Plate.

— TG504A1025: Blank face, internal thermometer.

— TG504A1033: External thermometer. See Fi

g

. 2.

Fig. 2. T874 Thermostat accessories.

Table 3. T874 Thermostat Specifications.

Models and Options Replaces Applications

System Stages

Anticipation

Heating (Adj) Cooling (Fixed)

Heat Cool Other Stage 1 Stage 2 Stage 1 Stage 2

T874A—Standard and TRADELINE®.

— 72°F/78°F

(

22°C/26°C

)

setpoint

stops with lockin

g

cover.

— Ad

j

ustable anticipator set 0.4A.

— Ad

j

ustable lockin

g

temperature

stops

(

TRADELINE®

)

.

— 72°F/78°F

(

22°C/26°C

)

setpoint

stops with lockin

g

cover, no

thermometer

(

for DoD

a

)

.

T872A Standard 1 1 — 0.1-1.2A — 0-1.5A —

T874B—Standard and TRADELINE. T872B Standard 1 2 — 0.1-1.2A — 0-1.2A 0-1.0A

T874C—Standard and TRADELINE.

— 72°F/78°F

(

22°C/26°C

)

set stops

with lockin

g

cover, no thermometer

(

for DoD

a

)

.

— 12°F

(

7°C

)

differential between

H1 and H2 sta

g

es

(

T874C1125

)

.

T872C Standard 2 1 — 0.1-1.2A 0.1-1.2A 0-1.5A —

— Fast c

y

clin

g

. 0.12-

0.6A

0.12-

0.6A

T874D—Standard and SUPER

TRADELINE®.

— Ad

j

ustable lockin

g

temperature

stops

(

SUPER TRADELINE

)

.

T872D Standard 2 2 — 0.1-1.2A 0.1-1.2A 0-1.2A 0-1.0A

T874E—Standard and TRADELINE. T872E 2-Sta

g

e Cool — 2 —— —0-1.2A 0-1.0A

T874F—Standard and TRADELINE.

— Lockin

g

cover.

T872F 2-Sta

g

e Heat 2 ——0.1-1.2A 0.1-1.2A ——

a

Department of Defense.

b

Chan

g

eover sta

g

e operates with heatin

g

.

c

Fixed volta

g

e t

y

pe anticipation.

d

Chan

g

eover sta

g

e operates with heatin

g

; a secondar

y

chan

g

eover is provided in coolin

g

switch.

e

Provides ni

g

ht setback used with standard T874 and timer-operated remote switchin

g

.

f

Manual chan

g

eover sta

g

e—use Q674B,L subbase.

g

Chan

g

eover sta

g

e operates with coolin

g

.

Q674 Subbases

194559R Locking Cover

with Thermometer

Allen Wrench

TG511D1004 Includes

Painted Steel Cover,

Opaque Base and Wallplate

TG504A1033 Key Lock

Cover with External

Thermometer

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

5 60-2485—8

Models:

See Table 4.

Electrical Ratings:

Switch Contacts: 2.5A at 30 Vac

(

7.5A inrush

)

.

LED Li

g

hts

(

Optional

)

: 30 Vac.

Switches:

Two slide switches

(

one switch on Q674G and K;

no switches on Q674D

)

operated b

y

levers. Switch position

is shown on scaleplate.

Mounting:

Desi

g

ned to mount horizontall

y

on an outlet box

or the wall. Adapter plate assembl

y

available for mountin

g

on a vertical outlet box

(

see Subbase Accessor

y)

.

Finish:

Dark brown or

g

ra

y

.

Dimensions in in. (mm):

3-1/2

(

89

)

hei

g

ht; 5-5/8

(

143

)

width;

5/16

(

8

)

depth. See Fi

g

. 1.

Table 4. Q674 Subbase Specifications.

— Fast c

y

clin

g

. Electric Heat 0.12-

0.6A

0.12-

0.6A

T874G—Heat pump, cool

chan

g

eover, with fast c

y

clin

g

.

T872G Heat Pump or

Standard

21

1

b

0-1.0A

c

0.1-1.2A 0-1.0A —

— Fixed anticipator for H2. 0.1-1.5A

— Fast c

y

clin

g

. 0.12-

0.6A

T874H—Use with Q674C. T872H Heat Pump or

Standard

11

1

b

0-1.0A

c

— 0-1.0A —

T874J—Heat pump. None Heat Pump 2 1

2

d

0-1.0A

e

0-1.5A

c

0-1.0A

c

—

T874K—Heat pump. None Heat Pump 2 1

1

b

0.1-1.2A

0-1.5A

c

0-1.5A —

T874L—Heat pump. None Heat Pump 2 1 — 0.1-1.2A 0.1-1.2A 0-1.5A —

T874N—Heat pump, heat

chan

g

eover.

T872N Heat Pump 2 1

1

b

0.1-1.2A 0.1-1.2A 0-1.0A —

T874P—Heat pump. None Heat Pump 2 1 — 0.1-1.2A 0.1-1.2A 0-1.5A —

T874Q—Ni

g

ht setback heatin

g

. T872Q Standard

1

e

——0.1-1.2A ———

T874R—Heat pump. T872R

Heat Pump

f

21—

0-1.5A

c

0.1-1.2A 0-1.5A —

T874S—Two-speed compressor heat

pump.

None Heat Pump 2 2

1

g

0-1.2A

c

0-1.2A

c

0-1.2A 0-1.0A

T874V—Standard. None Standard — 1 —— —0-1.5A —

T874W—Heat pump and standard.

— Ni

g

ht setback heatin

g

.

T872W Heat Pump or

Standard

32—

0-1.2A

b

0-1.2A

c,d

0-1.2A 0-1.0A

a

Department of Defense.

b

Chan

g

eover sta

g

e operates with heatin

g

.

c

Fixed volta

g

e t

y

pe anticipation.

d

Chan

g

eover sta

g

e operates with heatin

g

; a secondar

y

chan

g

eover is provided in coolin

g

switch.

e

Provides ni

g

ht setback used with standard T874 and timer-operated remote switchin

g

.

f

Manual chan

g

eover sta

g

e—use Q674B,L subbase.

g

Chan

g

eover sta

g

e operates with coolin

g

.

Q674 Subbases

Models and Options Replaces Application

Switch Positions

Use WithSystem Fan

Q674A—Standard and TRADELINE®.

— Indicator LEDs.

Q672A Standard HEAT-AUTO-COOL AUTO-ON T874A-D

Q674B—Standard and TRADELINE. Q672B Standard HEAT-OFF-COOL AUTO-ON T874A-D

— Provision for fan rela

y

operation from Heat Pump T874G,H,L,R

external fan switch

(

isolate G terminal

)

. OVERRIDE-HEAT- AUTO-ON T874P

— Indicator LEDs. OFF-COOL

Q674C—Standard and TRADELINE. Q672C Standard OFF-AUTO AUTO-ON T874A-H,W

— Indicator LEDs. Heat Pump OVERRIDE-AUTO- AUTO-ON T874K,L,N

OFF T874P

Q674D—Standard and TRADELINE.

— For use when subbase switchin

g

is not

re

q

uired.

Q672D Standard None None T874A-F

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

60-2485—86

Optional Specifications (Q674 Only):

Models available with up to four LEDs; for example, LEDs can

show EM. HT, AUX. HT, SERVICE, CHECK, FILTER, and

LOCKOUT. See Fi

g

. 3.

S

y

stem switchin

g

marked HEAT-OFF/RESET-COOL for s

y

s-

tems re

q

uirin

g

impedance rela

y

reset. Available on Q674B

onl

y

.

G terminal isolated on heatin

g

to provide fan rela

y

operation

from external low volta

g

e fan switch

(

Q674B onl

y)

.

Auto fan operation on both heat and cool.

L terminal is used for s

y

stem monitorin

g

devices.

Common R terminal for heatin

g

/coolin

g

.

Chan

g

eover in cool or heat mode for heat pumps.

Auto fan in EM.HT. for heat pumps.

Subbase Accessory:

193121A Adapter Plate Assembl

y

for

mountin

g

on vertical outlet box. Assembl

y

includes adapter

rin

g

and cover plate. Use to cover wall marks from

replaced thermostat.

Fig. 3. Heating, cooling levers and system LED indicators.

Q674E—Standard and TRADELINE. Q672E Standard OFF-HEAT-AUTO-

COOL

AUTO-ON T874A-D

Q674F—Two LED models.

— EM.HT. li

g

ht.

Q672F Heat Pump OFF-EM.HT.-HEAT-

AUTO-COOL

AUTO-ON T874C,D,G,N,S

— Provision for AUTO fan operation in

EM.HT.

OFF-COOL-AUTO-

HEAT-EM.HT.

AUTO-ON

Q674G—O and B terminals. Q672G Standard OFF-AUTO None T874A-F

Q674J—Provision for AUTO fan operation Q672J Heat Pump EM.HT.-AUTO-OFF AUTO-ON T874A,D,G,J

in EM.HT. EM.HT.-ON-OFF AUTO-ON

— Provision for outdoor thermistor. SUPL.HT.-ON-OFF AUTO-ON

Q674K—Standard. Q672K Standard OFF-HEAT-AUTO-

COOL

None T874F

OFF-WOOD-WOOD/

OIL-OIL

None

Q674L—Provision for AUTO fan operation in

EM.HT.

Q672L Heat Pump EM.HT.-HEAT-OFF-

COOL

AUTO-ON T874R,W

— Indicator LEDs. SUPL.HT.-HEAT-

OFF-COOL

AUTO-ON

Q674N—Standard. Q672N Evaporative

Cooler

EVAP-COOL-OFF-

HEAT

AUTO-ON T874C

Q674P—Standard. Q672P Heat Pump SUPL.HT.-HEAT-

COOL

AUTO-ON T874G

Q674Q—Standard. None Fan Coil HEAT-OFF-COOL LO-MED-HI-

ON

T874A

Q674R—Standard.

— International s

y

mbols.

None Fan Coil OFF-COOL LO-HI-

CONT.

T874V

Q674S—Indicator LED. None Standard HEAT-COOL None T874C

T874 Thermostat with

One Setpoint Lever

Q674 Subbase

with Four LEDs

T874 Thermostat with

Separate

Heatin

g

and Coolin

g

Levers

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

7 60-2485—8

MERCURY NOTICE

This control contains mercur

y

in a sealed tube. Do

not

place control in the trash at the end of its useful life.

If this control is replacin

g

a control that contains

mercur

y

in a sealed tube, do

not

place

y

our old control

in the trash.

Contact

y

our local waste mana

g

ement authorit

y

for

instructions re

g

ardin

g

rec

y

clin

g

and the proper

disposal of this control, or of an old control containin

g

mercur

y

in a sealed tube. If

y

ou have

q

uestions, call

the Hone

y

well Customer Response Center at

1-800-468-1502.

INSTALLATION

When Installing this Product…

1.

Read these instructions carefull

y

. Failure to follow them

could dama

g

e the product or cause a hazardous condi-

tion.

2.

Check the ratin

g

s

g

iven on the product to make sure the

product is suitable for

y

our application.

3.

Installer must be a trained, experienced service techni-

cian.

4.

After installation is complete, check out product opera-

tion as provided in these instructions.

CAUTION

Hazardous Voltage.

Can damage heating/cooling system.

1. Disconnect power suppl

y

before be

g

innin

g

instal-

lation to prevent electrical shock or e

q

uipment

dama

g

e.

2. Do

not

short across coil terminals on rela

y

. This

can burn out thermostat heat anticipator.

3. To prevent interference with the thermostat link-

a

g

e, keep wire len

g

th to a minimum and run wires

as close as possible to the subbase.

4. Do

not

overti

g

hten thermostat captive mountin

g

screws because dama

g

e to subbase threads can

result.

IMPORTANT

An incorrectly leveled thermostat will cause the tem-

perature control to deviate from setpoint. It is not a

calibration problem.

Location

Install the thermostat about 5 ft

(

1.5m

)

above the floor in an

area with

g

ood air circulation at avera

g

e temperature.

Do not mount the thermostat where it can be affected b

y

:

— drafts or dead spots behind doors, in corners or under

cabinets.

— hot or cold air from ducts.

— radiant heat from the sun, fireplace, or appliances.

— concealed pipes and chimne

y

s.

— unheated

(

uncooled

)

areas such as an outside wall behind

the thermostat.

Mount Subbase

The subbase can be mounted on a vertical outlet box,

horizontal outlet box or directl

y

on the wall.

1.

If the subbase is mounted on a vertical outlet box, order

Hone

y

well part no. 193121A Adapter Assembl

y

. See

Fi

g

. 4. The assembl

y

includes an adapter rin

g

, two

screws and a cover plate to cover marks on the wall.

Install the rin

g

and cover plate on the vertical outlet box.

NOTE: For a wall installation, hold subbase in position and

mark holes for anchors. See Fi

g

. 5. Wall anchors

must be obtained from local hardware store. Be

careful that the wires do not fall back into the wall

openin

g

. Set aside subbase. Drill four

3/16 in.

(

4.8 mm

)

holes and

g

entl

y

tap anchors into

the holes until flush with the wall.

2.

Pull wires throu

g

h the cover plate

(

if used

)

and subbase

cable openin

g

. See Fi

g

. 6.

3.

Secure the cover plate

(

if used

)

and subbase with the

screws provided. Do not full

y

ti

g

hten the subbase

screws.

Level the subbase usin

g

a spirit level, see Fi

g

. 7, and firml

y

ti

g

hten subbase mountin

g

screws. The subbase mountin

g

holes provide for minor out-of-level ad

j

ustments.

Fig. 4. Installing Q674 Subbase on outlet box.

M6009

VERTICAL

OUTLET

BOX

ADAPTER

RING

COVER

PLATE

MOUNTING

SCREWS (2)

1

SUBBASE

MOUNTING SCREWS (2)

HORIZONTAL

OUTLET

BOX

1

2

1 NOT INCLUDED WITH UNIT.

2 ACCESSORY PART AVAILABLE (193121A).

THERMOSTAT

CAPTIVE

MOUNTING SCREWS (2)

5

0

6

0

7

0

8

0

5

0

6

0

7

0

8

0

H

E

A

T

C

O

L

THERMOSTAT

COVER

5

0

6

0

7

0

8

0

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

60-2485—88

Fig. 5. Installing Q674 Subbase on wall.

Fig. 6. Subbase components and leveling procedure.

Wire Subbase

Disconnect power suppl

y

before be

g

innin

g

installation to

prevent electrical shock or e

q

uipment dama

g

e.

All wirin

g

must compl

y

with local electrical codes and

ordinances.

IMPORTANT

Use 18 gauge, solid-conductor wire whenever possi-

ble. If using 18 gauge stranded wire, no more than

10 wires can be used. Do not use larger than

18 gauge wire.

Follow e

q

uipment manufacturer wirin

g

instructions when

available. To wire subbase, proceed as follows:

1.

Connect the s

y

stem wires to the subbase as shown in

the applicable dia

g

ram. A letter code is located near

each terminal for identification. T

y

pical terminal desi

g

-

nation and wirin

g

connections are listed in Table 5. The

terminal barrier permits strai

g

ht or wraparound wirin

g

connection. See Fi

g

. 7. The subbase can re

q

uire one or

more

j

umpers that ma

y

or ma

y

not be factor

y

-supplied.

See Fi

g

. 8 and the wirin

g

dia

g

rams for specific terminals

to be

j

umpered.

Fig. 7. Barrier configuration.

CAUTION

Equipment Damage Hazard.

Never install more than one wire per terminal unless

usin

g

factor

y

-supplied

j

umper with spade terminal.

2.

Firml

y

ti

g

hten each terminal screw.

3.

Fit wires as close as possible to the subbase. Push

excess wire back into the hole.

4.

Plu

g

hole with nonflammable insulation to prevent drafts

from affectin

g

the thermostat.

WIRES THROUGH

WALL OPENING

WALL

ANCHORS

(2)

SUBBASE

MOUNTING

SCREWS (2)

M926

MOUNTING

HOLES

SPIRIT LEVEL

M927

WIRING

TERMINAL

THERMOSTAT

CABLE OPENING

TO SPRING FINGER

CONTACTS ON

THE THERMOSTAT

(

UP TO 12

)

MOUNTING

HOLES (4)

POST FOR

MOUNTING

THERMOSTAT (2)

FOR STRAIGHT

INSERTION

–

STRIP 5/16 IN. (8 MM)

FOR WRAPAROUND–

STRIP 7/16 IN. (11 MM)

SUBBASE TERMINAL SCREW

M928

BARRIER

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

9 60-2485—8

Fig. 8. Jumper adjacent terminals for special system hookup using stripped wire 3/4 in. (19 mm).

For nonadjacent terminals and using jumper wire supplied with subbase.

Table 5. Terminal Designations

a

Standard Terminal

Designation

Alternate Designations or

Customer Specials Typical Connection

BHeatin

g

damper motor; chan

g

eover valve

EKEmer

g

enc

y

heat rela

y

G F Fan rela

y

coil

LS

y

stem monitor

ORCoolin

g

damper motor; chan

g

eover valve

R V Power connection to transformer

(

internall

y

connected for heatin

g

and coolin

g)

RC Power connection to coolin

g

transformer

RH Power connection to heatin

g

transformer

W1 H1, R3 Sta

g

e 1 heatin

g

control

W2 H2, Y, R4 Sta

g

e 2 heatin

g

control

W3

Sta

g

e 3 heatin

g

control

b

Y1 C1, M Sta

g

e 1 coolin

g

control

Y2 C2 Sta

g

e 2 coolin

g

control

Y3 Sta

g

e 3 coolin

g

control

XX1,X2,CClo

gg

ed filter switch or common connection

T A Outdoor thermistor

L, C, H HSII control panel

PDefrost

O Momentar

y

circuit, chan

g

eover

A, A1, A2, Z, C, L LEDs

a

Other terminal desi

g

nations can be used that are not listed on this table. Refer to the hookup drawin

g

and internal schematic

for exact connections.

b

W3 controls the auxiliar

y

heat like W2, and allows addin

g

additional sta

g

es of auxiliar

y

heat with outdoor thermostats while

maintainin

g

the proper second sta

g

e anticipation.

M5899

1

1 TWO ADJACENT TERMINALS SHOWN JUMPERED ARE FOR EXAMPLE ONLY. COMPARE WIRING

DIAGRAM AND SUBBASE TO IDENTIFY TERMINALS TO BE JUMPERED.

JUMPER WIRE

(SUPPLIED WITH SOME MODELS)

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

60-2485—810

Outdoor Disconnect

The National Electrical Code re

q

uires the installation of a

disconnect switch w

ithin

si

g

ht of the outdoor unit of an air

conditioner or heat pump. The switch is for the safet

y

of an

y

technician workin

g

on the unit. The technician can assure that

the unit

remains

unpowered.

Install and Adjust Stop Brackets

The stop brackets should be installed onl

y

if there is a need to

restrict the ad

j

ustable ran

g

e of the heatin

g

and coolin

g

temperature setpoint levers. If ad

j

ustable lever stops are

desired, order 4074ECK Envelope Assembl

y

, which contains

two ad

j

ustable lever stop brackets, one brass insert, one

mountin

g

screw and two lockin

g

screws with insulated heads.

When installed, the stop brackets limit the movement of the

T874 HEAT and COOL levers.

TO INSTALL:

1.

Remove the thermostat cover b

y

pullin

g

the bottom

ed

g

e of the cover upward until it snaps free of the

mountin

g

slots.

2.

Turn to the back of the T874 Thermostat. Locate the

hole for the brass insert in the plastic base below the

LED window.

3.

Push the brass insert into the hole with fin

g

er.

4.

Turn to the front of the T874 Thermostat.

5.

Place the two stop brackets in position with the tabs in

the slot between the HEAT and COOL levers. See

Fi

g

. 9.

Fig. 9. Range limiting and lever locking methods.

6.

Insert the mountin

g

screw into the two slots in the stop

brackets and attach to the brass insert. Ti

g

hten the

screw to pull the brass insert into the back of the ther-

mostat.

7.

Loosen the mountin

g

screw enou

g

h to free the stop

brackets for ad

j

ustment.

T External temperature readout, T rela

y

R1, R2 LO and HI speed fan rela

y

s

RS Coolin

g

contactor

Y M Compressor contactor

Table 5. Terminal Designations

a

Standard Terminal

Designation

Alternate Designations or

Customer Specials Typical Connection

a

Other terminal desi

g

nations can be used that are not listed on this table. Refer to the hookup drawin

g

and internal schematic

for exact connections.

b

W3 controls the auxiliar

y

heat like W2, and allows addin

g

additional sta

g

es of auxiliar

y

heat with outdoor thermostats while

maintainin

g

the proper second sta

g

e anticipation.

HEAT

LEVER

HOLES FOR INSULATED

LOCKING LEVER SCREWS

COOL

LEVER

HOLE WITH

BRASS INSERT

BRACKET

TABS

ADJUSTABLE

LEVER STOP

BRACKETS

BRACKET

SLOTS

MOUNTING

SCREW

ADJUSTABLE STOPS

ADJUSTABLE LOCKING LEVERS

NONADJUSTABLE STOPS

WITH LOCKING LEVER SCREWS

75°F (24°C) MAX. HEAT

75°F (24°C) MIN. COOL

NONADJUSTABLE D.O.D. STOPS

72°F (22°C) MAX. HEAT

78°F

(

26°C

)

MIN. COOL

M7626

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

11 60-2485—8

8.

Move the HEAT and COOL levers to the maximum tem-

perature desired.

9.

Slide the stop brackets until one rests a

g

ainst the HEAT

lever and the other a

g

ainst the COOL lever.

10.

Firml

y

ti

g

hten the mountin

g

screw.

11.

If the HEAT and COOL levers are to be locked in place

at a specific temperature, use the two insulated head

screws supplied instead of the two ad

j

ustable lever stop

brackets.

CAUTION

Equipment Damage Hazard.

Do

not

use standard screws that provide metal-to-

metal contact with the stop brackets. Short circuit and

potential e

q

uipment dama

g

e can result.

Mount Thermostat

1.

Remove the thermostat cover b

y

pullin

g

the bottom

ed

g

e of the cover awa

y

from the base until it snaps free

of the cover clip.

NOTE: The cover is hin

g

ed at the top and must be removed

b

y

pullin

g

up at the bottom.

2.

Carefull

y

remove and discard the pol

y

st

y

rene packin

g

insert that protects the mercur

y

switches durin

g

ship-

ment.

3.

If LED indication

(

EM.HT., CHECK, etc.

)

is to be used

with the Q674 Subbase, install the preprinted insert

under the thermostat setpoint scale. To install, push

both thermostat setpoint levers to the far ends of the

thermostat. Use index fin

g

er to

g

entl

y

pull out the plastic

setpoint scale about 1/4 in.

(

6 mm

)

. Position the desired

preprinted insert in the space above the LED li

g

hts.

Reposition setpoint levers.

4.

Turn over the thermostat base and note the sprin

g

fin-

g

ers that en

g

a

g

e the subbase contacts. Make sure the

sprin

g

fin

g

ers are

not

bent flat, preventin

g

proper elec-

trical contact with the subbase.

5.

Set the heat anticipator indicator

(

s

)

to the respective

current settin

g

of each sta

g

e. See Set The Heat Antici-

pator section.

6.

If the thermostat provides optional lockin

g

cover assem-

bl

y

, start the Allen lockin

g

screws in the cover with the

wrench provided. See Fi

g

. 10.

7.

Note the two tabs alon

g

the top inside ed

g

e of the ther-

mostat base. The tabs fit into correspondin

g

slots on top

of the subbase. Mount the thermostat on the subbase.

8.

Ali

g

n the two captive mountin

g

screws in the thermostat

base with the posts on the subbase. Ti

g

hten both

screws.

Do not overtighten screws

or dama

g

e to sub-

base posts can result.

Fig. 10. Installation of locking cover assembly.

SETTINGS

CAUTION

Equipment Damage Hazard.

On s

y

stems usin

g

a

g

as valve, never appl

y

a

j

umper

across the valve coil terminals, even temporaril

y

. This

can burn out thermostat heat anticipator

(

s

)

.

Set the Heat Anticipator

Move the indicator to match the primar

y

control current draw.

When usin

g

a T874 Thermostat with two sta

g

es of heatin

g

,

set each heat anticipator to match its respective primar

y

control current draw. If

y

ou cannot find the current ratin

g

on

the primar

y

control, or if further ad

j

ustment is necessar

y

, see

NOTE and use the followin

g

procedure to determine the

current draw of each sta

g

e.

The current draw of each heatin

g

sta

g

e must be measured

with the thermostat removed and power on to the heatin

g

s

y

stem.

1.

Connect an ac ammeter of appropriate ran

g

e between

the heatin

g

terminals of the subbase:

a. Sta

g

e 1—between W1 and RH or R;

b. Sta

g

e 2—between W2 and RH or R

c. Sta

g

e 3—between W3 and RH or R.

2.

Move the s

y

stem switch to HEAT or AUTO.

3.

After one minute, read the ammeter and record the

readin

g

:

a. Sta

g

e 1—__________A;

b. Sta

g

e 2—__________A;

c. Sta

g

e 3—__________A.

NOTE: If e

q

uipment c

y

cles too fast, set the indicator to a

hi

g

her current ratin

g

, but not more than one-half divi-

sion at a time, and recheck the c

y

cle rate. Most con-

ventional two-sta

g

e heatin

g

e

q

uipment is desi

g

ned

to operate at three c

y

cles per hour per sta

g

e, and

one-sta

g

e heatin

g

e

q

uipment at six c

y

cles per hour,

at 50 percent load conditions. When usin

g

the T874

Thermostat in heat pump s

y

stems, set the heat

ALLEN

RETAINING

SCREWS (2)

M956

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

60-2485—812

anticipator at 140 percent of the actual primar

y

con-

trol current draw to reduce the c

y

clin

g

rate. See Fi

g

.

11.

Most heat pump s

y

stems should c

y

cle 2-1/2 to 3 times per hour.

4.

Han

g

the upper ed

g

e of the thermostat cover on top of

the thermostat base and swin

g

the cover downward

until it en

g

a

g

es with the cover clip.

Fig. 11. Adjustable heat anticipator scales.

Temperature Setting

Move the heatin

g

and coolin

g

levers to the desired comfort

positions. See Fi

g

. 12. On some models with two sta

g

es of

heatin

g

or coolin

g

, the same lever controls both sta

g

es. The

minimum differential between heatin

g

and coolin

g

setpoints is

4°F

(

2°C

)

(

5°F [3°C]

)

on T874W.

If model has optional screws to lock temperature control

levers, loosen these screws before makin

g

temperature

ad

j

ustment; ti

g

hten the screws when levers are set at desired

position.

Fig. 12. Internal view of T874W (three stages of

heating, two stages of cooling).

Subbase Setting

The subbase switchin

g

positions control the s

y

stem operation

as described below.

SYSTEM SWITCH

(

see subbase for positions

)

:

OFF—both the heatin

g

and coolin

g

s

y

stems are off. If the

fan switch is at the AUTO position, the coolin

g

fan is

also off.

HEAT—heatin

g

s

y

stem is automaticall

y

controlled b

y

the

thermostat. Coolin

g

s

y

stem is off.

AUTO—thermostat automaticall

y

chan

g

es between heat-

in

g

and coolin

g

s

y

stem operation, dependin

g

on the

indoor temperature.

COOL—coolin

g

s

y

stem is automaticall

y

controlled b

y

the

thermostat. Heatin

g

s

y

stem is off.

EM.HT.—emer

g

enc

y

heat rela

y

is automaticall

y

controlled

b

y

the thermostat. Coolin

g

s

y

stem is off. Compressor is

de-ener

g

ized.

SUPL.HT.—supplemental heat rela

y

is ener

g

ized. Coolin

g

s

y

stem is off. Compressor is de-ener

g

ized.

WOOD—heatin

g

s

y

stem is operatin

g

with onl

y

the wood-

burnin

g

sta

g

e.

OIL—heatin

g

s

y

stem is operatin

g

with onl

y

the oil-burnin

g

sta

g

e.

WOOD/OIL—wood and oil sta

g

es operate se

q

uentiall

y

;

first the WOOD sta

g

e operates, then the OIL sta

g

e

operates if the WOOD sta

g

e cannot handle the load.

EVAP—controls coolin

g

s

y

stem b

y

water evaporation; see

e

q

uipment instructions for further information.

OVERRIDE—ni

g

ht setback is disabled.

ON—heatin

g

s

y

stem is controlled b

y

the thermostat. EM.

HT. or SUPL. HT. rela

y

is not ener

g

ized.

FAN SWITCH

positions control fan operation as follows:

ON or CONT.—fan operates continuousl

y

.

AUTO—fan operates as controlled b

y

the thermostat in

heat pump s

y

stems or conventional coolin

g

mode; fan

operates as controlled b

y

the plenum switch in conven-

tional heatin

g

mode.

LO—fan operates constantl

y

at low speed.

MED—fan operates constantl

y

at medium speed.

HI—fan operates constantl

y

at hi

g

h speed.

To move the subbase switches to the desired control

positions, use thumb and index fin

g

er to slide the lever. The

lever must stop over desired function indicator position for

proper circuit operation.

Sprin

g

return momentar

y

position switchin

g

feature is

available on selected subbase models. On these models, the

fan switch is positioned to the ri

g

ht of the s

y

stem switch. B

y

movin

g

the fan switch to the far ri

g

ht and releasin

g

it, the ON

position circuit makes. The lever sprin

g

s back on release. This

position is not marked on the subbase.

Setting the Adjustable Differential

The ad

j

ustable intersta

g

e differential feature, on a selected

T874D model onl

y

, can be identified b

y

the scale and tension

screw near the heatin

g

and coolin

g

mercur

y

switches. See

Fi

g

. 13. On this model, the number of de

g

rees between the

makin

g

of the first and second sta

g

e mercur

y

bulbs is

ad

j

ustable. This feature is especiall

y

useful if the first sta

g

e

controls the comfort temperature, and the second sta

g

e

controls the ener

gy

savin

g

s temperature. Timers, such as the

S6005, for insertion between the first and second sta

g

e

control points must be ordered separatel

y

.

1.2

.4

.6

.3

.2

.15

.12

.1

0

.8

1.2

.4

.6

.3

.2

.15

.12

.8

.5

MOVE INDICATOR TO

MATCH CURRENT RATING

OF PRIMARY CONTROL

STAGE ONE

ANTICIPATOR

HEATING

CONTROL

STAGE TWO

ANTICIPATOR

HEATING CONTROL

M5069

STAGE 1

HEATING

STAGE 3

HEATING

STAGE 2

HEATING

LEVER

COOLING

LEVER

STAGE 1

COOLING

STAGE 2

COOLING

CAPTIVE

MOUNTING

SCREWS (2)

M7625

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

13 60-2485—8

Each mark on the scale represents 1°F

(

0.6°C

)

The

differential is factor

y

set at 2°F

(

1°C

)

the differential can be set

as hi

g

h as 12°F

(

7°C

)

To set the ad

j

ustable intersta

g

e

differential, loosen the tension screw. See Fi

g

. 13. Slide the

ad

j

ustable scale to ali

g

n with the number of de

g

rees desired

between sta

g

es. Use the lower ed

g

e of the tension screw

bracket as a

g

uide for ali

g

nment. In heatin

g

, slide the lever

wider

apart for a

larger

differential, or

closer

to

g

ether for a

smaller

differential. In coolin

g

, slide the lever

closer

to

g

ether

for a

larger

differential, or

wider

apart for a

smaller

differential.

While supportin

g

the scale with hand, ti

g

hten the tension screw.

IMPORTANT

Support the scale with hand while tightening tension

screw. See Fig. 13. Failure to do so can result in

twisting and damaging bimetal coil.

Fig. 13. Set adjustable interstage differential.

CAUTION

Equipment Damage Hazard.

When the thermostat is used to control a two-sta

g

e

heatin

g

or coolin

g

s

y

stem, the second sta

g

e mercur

y

bulb must never make before the first sta

g

e bulb, or

severe e

q

uipment dama

g

e could result. To prevent

this problem, provide at least 2°F

(

1°C

)

differential

between sta

g

e-one and sta

g

e-two make points.

Example: in heatin

g

, if sta

g

e-one makes at 70°F

(

21°C

)

sta

g

e-two should make at 68°F

(

20°C

)

or lower.

Verify the Adjustment

Heating

Start with the heatin

g

setpoint lever all the wa

y

to the left.

Slowl

y

move the lever to the ri

g

ht,

j

ust until the first sta

g

e bulb

makes

(

mercur

y

rolls to the ri

g

ht side of the bulb

)

. Note the

settin

g

on the temperature scale. Slowl

y

move the lever to the

ri

g

ht until the second sta

g

e bulb makes. Note the settin

g

on

the temperature scale. The difference between the two

temperatures is the

interstage differential,

which should match

the number set on the scale with the tension screw.

Cooling

Start with the coolin

g

setpoint lever all the wa

y

to the ri

g

ht.

Slowl

y

move the lever to the left,

j

ust until the first sta

g

e bulb

makes

(

mercur

y

rolls to the left side of the bulb

)

. Note the

settin

g

on the temperature scale. Slowl

y

move the lever to the

left until the second sta

g

e bulb makes. Note the settin

g

on the

temperature scale. The difference between the two

temperatures is the

interstage differential,

which should match

the number set on the scale with the tension screw.

CHECKOUT

Heating

Move the s

y

stem switch on the Q674 Subbase to HEAT or

AUTO. Move the heat lever on the T874 about 10°F

(

6°C

)

above room temperature. See Fi

g

. 12. Heatin

g

s

y

stem should

start and the fan should run after a short dela

y

. Move the heat

lever about 10°F

(

6°C

)

below room temperature. The heatin

g

e

q

uipment should shut off, and the fan should run for a short

time, then shut off.

In heat pump applications, sometimes time dela

y

s are

involved before the compressor and auxiliar

y

heat are

activated. This is due to a minimum-off timer, which prevents

the compressor from restartin

g

for five minutes from when the

thermostat last turned off the compressor, or from when the

s

y

stem first received power.

Cooling

CAUTION

Equipment Damage Hazard.

Do not operate coolin

g

if outdoor temperature is below

50°F

(

10°C

)

. Refer to manufacturer recommendations.

TENSION

SCREW

ALIGN LOWER

EDGE WITH

SCALE

NOTCH

10°F

SCALE

1

SLIDE LEVER

WIDER APART

FOR LARGER

DIFFERENTIAL

HEATING

TENSION

SCREW

ALIGN LOWER

EDGE WITH

SCALE

NOTCH

4°F

SCALE

1

SLIDE LEVER

CLOSER TOGETHER

FOR LARGER

DIFFERENTIAL

COOLING

1 EACH MARK ON THE SCALE REPRESENTS 1°F (0.6°C).

M937

1.2

.8

.6

.3

.2

1

.5

.4

50 60

70 80

HEAT

TENSION

SCREW

HEATING SET-

POINT LEVER

FIRST

STAGE

SWITCH

SECOND STAGE

(ADJUSTABLE)

SWITCH

SCALE

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

60-2485—814

Move the s

y

stem switch on the Q674 Subbase to COOL or

AUTO. Move the cool settin

g

lever on the T874 Multista

g

e

Thermostat about 10°F

(

6°C

)

below room temperature. See

Fi

g

. 12. The coolin

g

e

q

uipment and fan should start. If the

s

y

stem has two sta

g

es of coolin

g

, both sta

g

es should start.

Move the cool lever about 10°F

(

6°C

)

above room

temperature. The coolin

g

e

q

uipment and fan should stop.

Fan

Move the s

y

stem switch to COOL, OFF, or AUTO. If

necessar

y

, position both temperature settin

g

levers so that the

heatin

g

and coolin

g

e

q

uipment are off. Move the fan switch to

ON or CONT. The fan should run continuousl

y

. When the fan

switch is in AUTO, LO, MED, or HI position, fan operation is

controlled b

y

the heatin

g

or coolin

g

s

y

stem.

Outdoor Reset Thermistor (Where

Applicable)

If the s

y

stem is supplied with a thermistor, it must be used; if

not used, thermostat performance deviates radicall

y

from

proper operation.

The proper thermistor operation must be verified to ensure the

correct operation of the thermostat. Check thermistor

operations as follows:

1.

Disconnect the T wire on the subbase.

2.

Use an ohmmeter to measure resistance between the

T wire and the A subbase terminal.

3.

Take outdoor temperature at thermistor location and find

the correct thermistor resistance on the Fi

g

. 14 chart.

4.

If the resistance measured in step 2 and the calculated

resistance in step 3 var

y

b

y

more than 15 percent, the

thermistor re

q

uires replacement. Contact Hone

y

well or

installin

g

dealer for replacement packa

g

ed outdoor ther-

mistor, part no. C815A1005.

Fig. 14. Thermistor resistance chart.

CALIBRATION

Thermostat

T874 Thermostats are accuratel

y

calibrated at the factor

y

.

They do not have provision for field calibration.

Thermometer

The thermometer in

y

our thermostat has been accuratel

y

calibrated at the factor

y

. The thermometer should onl

y

need

ad

j

ustment if it has been dropped or shifted due to mishandlin

g

.

If the setpoint lever and the thermometer readin

g

do not

a

g

ree, use the followin

g

procedure:

1.

Remove the thermostat cover b

y

pullin

g

up from the

bottom ed

g

e of the cover awa

y

from the base until it

snaps free of the cover clip.

2.

Set the thermostat cover on a table near an accurate

thermometer.

3.

Allow ten minutes for cover thermometer to sense area

temperature; compare the readin

g

s. Be careful not to

touch thermometer or breathe on it.

4.

If the readin

g

s are the same, replace cover and put the

s

y

stem into operation.

5.

If the readin

g

s are different, insert a small screwdriver in

the thermometer slot and turn it until the thermometers

have the same readin

g

. See Fi

g

. 15.

6.

Replace thermostat cover and put the s

y

stem into oper-

ation.

Fig. 15. Thermometer calibration.

UNDERSTANDING CIRCUITS

To understand wirin

g

dia

g

rams, it is important to know what all

the s

y

mbols mean and how to trace the path of the circuits

from the transformer. See Fi

g

. 16 throu

g

h 25.

Circuit descriptions and terminolo

gy

are defined as follows:

For standard heatin

g

-coolin

g

circuits:

Auto chan

g

eover—refers to the presence of an AUTO

position in the s

y

stem switchin

g

(

EX: Q674E with OFF-

HEAT-AUTO-COOL switchin

g)

. The thermostat auto-

maticall

y

chan

g

es between heat and cool modes as

indoor temperature chan

g

es.

Manual chan

g

eover—re

q

uires a s

y

stem switch movement

to chan

g

e mode

(

EX: Q674B with HEAT-OFF-COOL

switchin

g)

. T874D Multista

g

e Thermostats with 2 heat

or 2 cool switches are shown on most standard circuits.

Most standard or TRADELINE® subbases

(

Q674A-E,G

)

can be used with T874A-F standard or TRADELINE

THERMISTOR RESISTANCE (ohms)

C815A THERMISTOR RESISTANCE

R = 400 ohms ± 10% AT 77°F (25°C)

4600

4400

4200

4000

3800

3600

3400

3200

3000

2800

2600

2400

2200

2000

1800

1600

1400

1200

1000

800

600

400

200

0

-20 0 20 40 60 80 100 120 140

TEMPERATURE OF THERMISTOR

(

°F

)

M1590A

M5070

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

15 60-2485—8

thermostats. The schematics can be field-modified as

re

q

uired

(

EX: if T874C is bein

g

used, eliminate second

sta

g

e of heat

)

.

For heat pump circuits:

Cool chan

g

eover valve—operates on coolin

g

. The revers-

in

g

valve or rela

y

is activated either b

y

movin

g

the s

y

s-

tem switch to COOL

(

manual chan

g

eover

)

or b

y

a

mercur

y

switch that makes on a temperature rise

(

auto

chan

g

eover

)

.

Heat chan

g

eover valve—operates on heatin

g

. The revers-

in

g

valve or rela

y

is activated either b

y

movin

g

the s

y

s-

tem switch to HEAT

(

manual chan

g

eover

)

or b

y

a

mercur

y

switch that makes on a temperature fall

(

auto

chan

g

eover

)

.

S

y

stem monitor rela

y

—optional e

q

uipment on some heat

pumps includes an R4222P1065 or e

q

uivalent. This

s

y

stem monitor rela

y

detects a malfunction in the com-

pressor and indicates the malfunction b

y

activatin

g

the

EMERGENCY HEAT LED on the Q674 Switchin

g

Sub-

base. The s

y

stem monitor rela

y

is usuall

y

wired into the

L terminal on the Q674.

Each mercur

y

switch is identified b

y

function:

H1—Sta

g

e 1 Heatin

g

.

H2—Sta

g

e 2 Heatin

g

.

H3—Sta

g

e 3 Heatin

g

.

C1—Sta

g

e 1 Coolin

g

.

C2—Sta

g

e 2 Coolin

g

.

C3—Sta

g

e 3 Coolin

g

.

C/O—Chan

g

eover

(

heat pumps

)

.

Each anticipator is identified and each switch affected is

named

(

EX: H1 anticipator, C1 anticipator

)

.

All T874 Multista

g

e Thermostats use mercur

y

switches. Each

schematic indicates switch operation b

y

bein

g

drawn in the

open position with an arrow indicatin

g

operation with a

temperature RISE or FALL.

One circuit has been selected that is t

y

pical of various models

used with heat pumps. This circuit has been traced to

illustrate the functions performed b

y

these control s

y

stems.

Tracing Method:

1.

Alwa

y

s be

g

in at the s

y

stem transformer or R terminal.

You ma

y

want to draw the switch contacts in each

switch position to aid in tracin

g

. Colored pencils are

helpful when onl

y

one cop

y

of the circuit is available.

See Fi

g

. 16 for a description of the hookup s

y

mbols and

Fi

g

. 17 throu

g

h 25 for t

y

pical hookups.

2.

Completel

y

trace onl

y

one circuit at a time

(

for example:

heat or cool

)

.

3.

Connections are indicated b

y

small dots at the point of

intersection. If there is no dot, there is no connection.

4.

The left portion of the circuit

(

the thermostat

)

contains

the mercur

y

switches. The heat switches make on a

temperature fall, and the cool switches make on a tem-

perature rise. Fixed anticipation is represented b

y

a zi

g

-

za

g

line and ad

j

ustable anticipation is a zi

g

za

g

with an

arrow. The resistance of the fixed anticipator is so lar

g

e

it limits current so that a s

y

stem rela

y

cannot be pulled

in from a circuit path

g

oin

g

throu

g

h the fixed anticipator.

The rela

y

can be pulled in throu

g

h an ad

j

ustable antici-

pator because its resistance is

g

enerall

y

0 to 5 ohms.

5.

The center portion

(

the subbase

)

contains the switches.

The fan switch is above the s

y

stem switch. The small

circles on the switch represent the maximum possible

contacts available on the Q674 Subbase. The lar

g

er cir-

cles represent the switch positions available on this par-

ticular Q674, with the solid circle representin

g

where it

is actuall

y

switched on the dia

g

ram.

NOTE: Solid circles are not interconnected electricall

y

.

At the ri

g

ht, the rela

y

s and contactors are shown, attached to

the proper terminals. The terminals are represented b

y

lar

g

e

circles with terminal desi

g

nations in capital letters. See Table

3 for the meanin

g

of each lettered terminal.

Sometimes power for a fixed anticipator is brou

g

ht throu

g

h an

off s

y

stem rela

y

like the chan

g

eover rela

y

shown in Fi

g

. 20.

This current is kept low b

y

the hi

g

h resistance of the fixed

anticipator so that rela

y

does not pull in.

Fig. 16. Key to hookup symbols.

M5848

KEY TO HOOKUP SYMBOLS

TRANSFORMER

(24 VAC SECONDARY)

RELAY/CONTACTOR CONTACTS

LED

RELAY OR CONTACTOR COIL

MERCURY SWITCH

FIXED ANTICIPATOR

HIGH RESISTANCE

(TYPICALLY 5 KILOHMS)

ADJUSTABLE ANTICIPATOR

LOW RESISTANCE

(TYPICALLY 0 TO 5 OHMS)

TERMINAL

ODT

OUTDOOR THERMOSTAT

EHR

EMERGENCY HEAT RELAY

RTD

TIME DELAY RELAY

RD

DEFROST RELAY

CHP

PRESSURE SWITCH

LACO

LOW AMBIENT CUTOFF

B

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

60-2485—816

Fig. 17. Internal schematic and typical hookup of a T874R Thermostat and Q674L Subbase in a heat pump application.

The thermostat provides two-stage heating and one-stage cooling manual changeover operates on cooling.

M5072A

(HOT) L1

L2

1

LACO

CHP

Y

B

E

O

G

L

X

W2

W3

R

ODT 1

RTD 1 EHR 1

RTD 2

ODT 2

EHR 2 RTD 3

RD

SYSTEM

MONITOR

FAN RELAY

COMPRESSOR

CONTACTOR

COOL CHANGEOVER

VALVE

EM. HT.

RELAY

RTD 1

AUX. HT.

LED

(GREEN)

EM. HT.

LED (RED)

FAN SWITCH

ON

AUTO

SYSTEM

SWITCH

EM. HT.

HEAT

OFF

COOL

H2

FALL

H1

FALL

C1

2

3

4

5

6

H1/C1

ANTICIPATOR

H2

ANTICIPATOR

1

POWER SUPPLY. PROVIDE DISCONNECT MEANS AND OVERLOAD PROTECTION AS REQUIRED.

AUXILIARY HEAT LED AVAILABLE ON SOME MODELS.

THERMOSTAT

SUBBASE

SYSTEM COMPONENTS

2

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

17 60-2485—8

Fig. 18. Tracing the changeover relay circuit.

Fig. 19. Tracing the heat 1 and anticipation circuit.

M5840

L1

(HOT)

L2

1

LACO

CHP

Y

B

E

O

G

L

X

W2

W3

R

ODT 1

RTD 1 EHR 1

RTD 2

ODT 2

EHR 2 RTD 3

RD

SYSTEM

MONITOR

FAN RELAY

COMPRESSOR

CONTACTOR

CHANGEOVER

VALVE

EM. HT.

RELAY

RTD 1

AUX. HT.

LED

(GREEN)

EM. HT.

LED (RED)

FAN SWITCH

ON

AUTO

SYSTEM

SWITCH

EM. HT.

HEAT

OFF

COOL

H2

FALL

H1

FALL

C1

2

3

4

5

6

H1/C1

ANTICIPATOR

H2

ANTICIPATOR

1

POWER SUPPLY. PROVIDE

DISCONNECT MEANS AND

OVERLOAD PROTECTION

AS REQUIRED.

THERMOSTAT

SUBBASE SYSTEM COMPONENTS

M5841

L1

(HOT)

L2

1

LACO

CHP

Y

B

E

O

G

L

X

W2

W3

R

ODT 1

RTD 1

EHR 1

RTD 2

ODT 2

EHR 2 RTD 3

RD

SYSTEM

MONITOR

FAN RELAY

COMPRESSOR

CONTACTOR

CHANGEOVER

VALVE

EM. HT.

RELAY

RTD 1

AUX. HT.

LED

(GREEN)

EM. HT.

LED (RED)

FAN SWITCH

ON

AUTO

SYSTEM

SWITCH

EM. HT.

HEAT

OFF

COOL

H2

FALL

H1

FALL

C1

2

3

4

5

6

H1/ C1

ANTICIPATOR

H2

ANTICIPATOR

1

POWER SUPPLY. PROVIDE

DISCONNECT MEANS AND

OVERLOAD PROTECTION

AS REQUIRED.

THERMOSTAT SUBBASE

SYSTEM COMPONENTS

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

60-2485—818

Fig. 20. Tracing the heat 1 anticipation circuit.

Fig. 21. Tracing the heat 2, anticipation and AUX. HT. LED circuit.

M5842

L1

(HOT)

L2

1

LACO

CHP

Y

B

E

O

G

L

X

W2

W3

R

ODT 1

RTD 1 EHR 1

RTD 2

ODT 2

EHR 2 RTD 3

RD

SYSTEM

MONITOR

FAN RELAY

COMPRESSOR

CONTACTOR

CHANGEOVER

VALVE

EM. HT.

RELAY

RTD 1

AUX. HT.

LED

(GREEN)

EM. HT.

LED (RED)

FAN SWITCH

ON

AUTO

SYSTEM

SWITCH

EM. HT.

HEAT

OFF

COOL

H2

FALL

H1

FALL

C1

2

3

4

5

6

H1/ C1

ANTICIPATOR

H2

ANTICIPATOR

1

POWER SUPPLY. PROVIDE

DISCONNECT MEANS AND

OVERLOAD PROTECTION

AS REQUIRED.

THERMOSTAT SUBBASE

SYSTEM COMPONENTS

M5843

L1

(HOT)

L2

1

LACO

CHP

Y

B

E

O

G

L

X

W2

W3

R

ODT 1

RTD 1 EHR 1

RTD 2

ODT 2

EHR 2 RTD 3

RD

SYSTEM

MONITOR

FAN RELAY

COMPRESSOR

CONTACTOR

CHANGEOVER

VALVE

EM. HT.

RELAY

RTD 1

AUX. HT.

LED

(GREEN)

EM. HT.

LED (RED)

FAN SWITCH

ON

AUTO

SYSTEM

SWITCH

EM. HT.

HEAT

OFF

COOL

H2

FALL

H1

FALL

C1

2

3

4

5

6

H1/C1

ANTICIPATOR

H2

ANTICIPATOR

1

POWER SUPPLY. PROVIDE

DISCONNECT MEANS AND

OVERLOAD PROTECTION

AS REQUIRED.

THERMOSTAT SUBBASE

SYSTEM COMPONENTS

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

19 60-2485—8

Fig. 22. Tracing the emergency heat and EM. HT. LED circuit.

Fig. 23. Tracing the cooling circuit.

M5844

L1

(HOT)

L2

1

LACO

CHP

Y

B

E

O

G

L

X

W2

W3

R

ODT 1

RTD 1 EHR 1

RTD 2

ODT 2

EHR 2 RTD 3

RD

SYSTEM

MONITOR

FAN RELAY

COMPRESSOR

CONTACTOR

CHANGEOVER

VALVE

EM. HT.

RELAY

RTD 1

AUX. HT.

LED

(GREEN)

EM. HT.

LED (RED)

FAN SWITCH

ON

AUTO

SYSTEM

SWITCH

EM. HT.

HEAT

OFF

COOL

H2

FALL

H1

FALL

C1

2

3

4

5

6

H1/C1

ANTICIPATOR

H2

ANTICIPATOR

1

POWER SUPPLY. PROVIDE

DISCONNECT MEANS AND

OVERLOAD PROTECTION

AS REQUIRED.

THERMOSTAT SUBBASE

SYSTEM COMPONENTS

M5845

L1

(HOT)

L2

1

LACO

CHP

Y

B

E

O

G

L

X

W2

W3

R

ODT 1

RTD 1 EHR 1

RTD 2

ODT 2

EHR 2 RTD 3

RD

SYSTEM

MONITOR

FAN RELAY

COMPRESSOR

CONTACTOR

CHANGEOVER

VALVE

EM. HT.

RELAY

AUX. HT.

LED

(GREEN)

EM. HT.

LED (RED)

FAN SWITCH

ON

AUTO

SYSTEM

SWITCH

EM. HT.

HEAT

OFF

COOL

H2

FALL

H1

FALL

C1

2

3

4

5

6

H1/C1

ANTICIPATOR

H2

ANTICIPATOR

1

POWER SUPPLY. PROVIDE

DISCONNECT MEANS AND

OVERLOAD PROTECTION

AS REQUIRED.

THERMOSTAT SUBBASE

SYSTEM COMPONENTS

RTD 1

T874 MULTISTAGE THERMOSTATS AND Q674 SUBBASES

60-2485—820

Fig. 24. Tracing the auto fan circuit.

Fig. 25. Tracing the fan on circuit.

M5846

L1

(HOT)

L2

1

LACO

CHP

Y

B

E

O

G

L

X

W2

W3

R

ODT 1

RTD 1 EHR 1

RTD 2

ODT 2

EHR 2 RTD 3

RD

SYSTEM

MONITOR

FAN RELAY

COMPRESSOR

CONTACTOR

CHANGEOVER

VALVE

EM. HT.

RELAY

RTD 1

AUX. HT.

LED

(GREEN)

EM. HT.

LED (RED)

FAN SWITCH

ON

AUTO

SYSTEM

SWITCH

EM. HT.

HEAT

OFF

COOL

H2

FALL

H1

FALL

C1

2

3

4

5

6

H1/C1

ANTICIPATOR

H2

ANTICIPATOR

1

POWER SUPPLY. PROVIDE

DISCONNECT MEANS AND

OVERLOAD PROTECTION

AS REQUIRED.

THERMOSTAT SUBBASE

SYSTEM COMPONENTS

M5847

L1

(HOT)

L2

1

LACO

CHP

Y

B

E

O

G

L

X

W2

W3

R

ODT 1

RTD 1 EHR 1

RTD 2

ODT 2

EHR 2 RTD 3

RD

SYSTEM

MONITOR

FAN RELAY

COMPRESSOR

CONTACTOR

CHANGEOVER

VALVE

EM. HT.

RELAY

RTD 1

AUX. HT.

LED

(GREEN)

EM. HT.

LED (RED)

FAN SWITCH

ON

AUTO

SYSTEM

SWITCH

EM. HT.

HEAT

OFF

COOL

H2

FALL

H1

FALL

C1

2

3

4

5

6

H1/C1

ANTICIPATOR

H2

ANTICIPATOR

1

POWER SUPPLY. PROVIDE

DISCONNECT MEANS AND

OVERLOAD PROTECTION

AS REQUIRED.

THERMOSTAT SUBBASE

SYSTEM COMPONENTS

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