Bryant Thermostat Q674 User manual

Category
Heat pumps
Type
User manual

This manual is also suitable for

PRODUCT DATA
60- 248
5
-
8
® U.S. Re
g
istered Trademark
Cop
y
ri
g
ht © 2001 Hone
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
ustable temperature lockin
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
uardâ„¢ 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
50 60 70 80
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
SUBBASE
MOUNTING SCREWS (2)
HORIZONTAL
OUTLET
BOX
1
2
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
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
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
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
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
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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Bryant Thermostat Q674 User manual

Category
Heat pumps
Type
User manual
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