Contents
Model nomenclature ............................................................ 2
Transportation and shortage ................................................ 2
Installation ....................................................................... 2–4
Electrical data ...................................................................... 5
Piping ............................................................................... 5,6
Cleaning and flushing system .............................................. 6
Start-up ........................................................................... 6, 7
Operating limits ................................................................... 7
Wiring diagrams ............................................................. 8–14
Unit operation .................................................................... 15
LED Status and Fault Output Status .................................. 16
Thermostat Connections, Mark IV/AC units ....................... 17
Options for Mark IV/AC units ....................................... 19–22
Troubleshooting ................................................................. 23
Maintenance ...................................................................... 24
©2006 McQuay International
®
Installation & Maintenance Data IM 407-16
Group: WSHP
Part Number: 106581203
Date: June 2006
Vertical Water Source Heat Pump
& Cooling Only Units
Models FDD, FDE, FDL, FDS, FME, FMS
Page 2 of 24 / IM 407
Installation
General
1. To prevent damage, this equipment should not be oper-
ated for supplementary heating and cooling during the
construction period.
2. Inspect the carton for any specific tagging numbers as
requested by the installing contractor. At this time the
voltage, phase and capacity should be checked against
the plans.
3. Check the unit size against the plans to be sure that the
unit will be installed in the correct location.
4. Before installation, check the available closet dimensions
versus the dimensions of the unit.
5. Pay attention to the location and routing of water piping,
and electrical wiring. The locations of these items are
clearly marked on submittal drawings.
6. The installing contractor will find it beneficial to confer
with piping, sheet metal, ceiling and electrical foremen
together before installing any conditioners.
7. Remove shipping block from under the fan wheel.
8. We recommend that the contractor cover the condition-
ers with plastic film to protect the machines during finish-
ing of the building. This is important if spraying fireproof-
ing material on bar joists, sandblasting, spray painting
and plastering operations have not been completed. If
plastic film is not available, the shipping carton may be
modified to cover the units during construction.
9. On extra-quiet construction units with spring mounted
compressors, remove the shipping block under the com-
pressor.
Transportation and Storage
Upon receipt of the equipment, check carton for visible
damage. Make a notation on the shipper’s delivery ticket
before signing. If there is any evidence of rough handling, the
cartons should be opened at once to check for concealed
damage. If any damage is found, notify the carrier within 48
hours to establish your claim and request their inspection
and a report. The Warranty Claims Department should then
be contacted.
Do not stand or transport the machines on end. For
storing, each carton is marked with “up” arrows.
In the event that elevator transfer makes upended posi-
tioning unavoidable, absolutely insure that the machine is in
the normal upright position for at least 24 hours before
operating.
Temporary storage at the jobsite must be indoors, com-
pletely shielded from rain, snow, etc. High or low tempera-
tures naturally associated with weather patterns will not
harm the conditioners. Excessively high temperatures of
140
o
F (60
o
C) may deteriorate certain plastic materials and
cause permanent damage. In addition, the solid-state circuit
boards may experience operational problems.
Note: Installation and maintenance are to be performed only by qualified personnel who are familiar with local codes and
regulations, and are experienced with this type of equipment. Caution: Sharp edges are a potential injury hazard. Avoid contact
with them.
Model Nomenclature
W FDD 1 009 E Z
Product Category
W = WSHP
Product Identifier
See box below
Design Series
1 = A Design
2 = B Deisgn
3 = C Design
4 = D Design
5 = E Design
Nominal Capacity
007 = 7,000
009 = 9,000
012 = 12,000
015 = 15,000
019 = 19,000
etc. . .
Coil Options
(None)
Voltage
E= 208/230-60-1
F= 208/230-60-3
J= 265-60-1
K= 460-60-3
L= 575-60-3
M= 230-50-1
N= 380-50-3
McQuay Product Identifiers
FDD = Floor Mtd/DDC Controls/Ext. Range/Less Board FDS = Floor Mtd/DDC Controls/Std. Range
FDE = Floor Mtd/DDC Controls/Ext. Range FME = Floor Mtd/Mark IV/Ext. Range
FDL = Floor Mtd/DDC Controls/Std. Range/Less Board FMS = Floor Mtd/Mark IV/Std. Range
IM 407 / Page 3 of 24
Unit location
1. Locate the unit in an area that allows for easy removal of
the filter and access panels, and has enough space for
service personnel to perform maintenance or repair. Pro-
vide sufficient room to make water, electrical and duct
connections.
2. The contractor should make sure that access has been
provided including clearance for duct collars and fittings
at water and electrical connections.
3. Allow adequate room around the unit for a condensate
trap.
4. The unit can be installed “free standing” in an equipment
room; however, closet installations are more common for
small vertical type units. Generally, the unit is located in
the corner of a closet with the nonducted return air facing
90
o
to the door and the major access panels facing the
door as in Figure 1A. Alternatively, the unit can have a
ducted return air with the opening facing the door and the
major access panels facing 90
o
to the door as in Figure 1B.
Figure 1A. Typical closet installation with louver door return
Figure 1B. Typical closet installation with ducted return
Heat Pump
With Left-Hand
Return Air Arrangement
Return
Air
Elec. Entrance
Opt. Controls
Main Access Panel
Condensate
Water Supply
Water Return
Heat Pump
With Right-Hand
Return Air Arrangement
Return
Air
Opt. Controls
Elec. Entrance
Main Access Panel
Condensate
Water Supply
Water Return
Return Air Thru
Louvered Door
RisersReturn Air Thru
Louvered Door
Heat Pump
With Left-Hand
Return Air Arrangement
Heat Pump
With Right-Hand
Return Air Arrangement
Main Access Panel Main Access Panel
Elec. Entrance
Opt. Controls
Elec. Entrance
Opt. Controls
Water Return
Condensate
Risers
Condensate
Water Supply
Water Return
Water Supply
Return
Air
Duct &
Grille
Return
Air
Duct &
Grille
5. It is recommended that the unit be located on top of a
vibration absorbing material such as rubber or carpet to
reduce any vibration. See Figure 5.
6. If optional field installed controls are required (boilerless
system), space must be provided for the enclosure to
mount around the corner from the electrical entrances. Do
not locate the side of the unit too close to a wall. See
Figures 1A and 1B.
Minimum distance requirement from return air duct
collar to wall, for non-ducted units.
Model Distance
007 – 012 .......................... 4 inches
015 – 019 .......................... 5 inches
024 – 030 .......................... 6 inches
036 – 042 .......................... 7 inches
048 – 060 .......................... 8 inches
Filter access
Each unit is shipped with a filter bracket for side filter re-
moval.
NOTE: Minimum distance
requirement for non-ducted
units. (see chart above)
Page 4 of 24 / IM 407
Ductwork and attenuation
Discharge ductwork is normally used with these condition-
ers. Return air ductwork may also be required, but will require
field installation of a return air duct collar/2" (51mm) filter rack
kit.
All ductwork should conform to industry standards of
good practice as described in ASHRAE Systems Guide.
The discharge duct system will normally consist of a
flexible connector at the unit, a noninsulated transition piece
to the full duct size, a short run of duct, an elbow without
vanes, and a trunk duct teeing into a branch circuit with
discharge diffusers as shown in Figure 2. The transition piece
must not have an angle greater than 30
o
or severe loss of air
performance can result. Do not connect the full duct size to
the unit without using a transition piece down to the size of
the discharge collar on the unit. With metal duct material, the
sides only of the elbow and entire branch duct should be
internally lined with acoustic insulation for sound attenua-
tion. Glass fiber duct board material is more absorbing and
may permit omission of the flexible connector.
The ductwork should be laid out so that there is no line of
sight between the conditioner discharge and the distribution
diffusers.
Return air ducts can be brought in through a wall grille and
then to the unit. The return duct system will normally consist
of a flexible connector at the unit and a trunk duct to the
return air grille. With metal duct material, the return air duct
should be internally lined with acoustic insulation for sound
attenuation. Glass fiber duct board material is more absorb-
ing and may permit omission of the flexible connector.
Return air ductwork to the unit requires the optional return
air duct collar/2" (51mm) filter rack kit. See Figure 3. The kit
can be installed for face side or bottom filter removal. The
flexible connector can then be attached to the 1" (25mm)
duct collar.
Do not use sheet metal screws directly into the unit
cabinet for connection of supply or return air ductwork,
especially return air ductwork which can puncture the drain
pan or the air coil.
Figure 2.
Ventilation air
Outside air may be required for ventilation. The temperature
of the ventilation air must be controlled so that mixture of
outside air and return air entering the conditioner does not
exceed application limits. It is also general practice to close
off the ventilation air system during unoccupied periods
(night setback).
The ventilation air system is generally a separate building
subsystem with distribution ductwork. Simple introduction
of the outside air into each return air plenum chamber
reasonably close to the conditioner air inlet is not only
adequate, but recommended. Do not duct outside air directly
to the conditioner inlet. Provide sufficient distance for thor-
ough mixing of outside and return air. See “Operating limits”
on page 7.
Figure 3.
Sizes 007 thru 042 Sizes 048 & 060
Heat Pump
Duct
Transition
Discharge Collar
(on Heat Pump)
Square Elbow
(Both Sides
Internally Lined
With Acoustic
Insulation)
Trunk Duct
Branch Duct
(Internally
Lined)
2 ft. x 2 ft
Diffuser
Canvas
Collar
IM 407 / Page 5 of 24
Electrical Data
General
1. Be sure the available power is the same voltage and phase
as that shown on the unit serial plate. Line and low voltage
wiring must be done in accordance with local codes or the
National Electrical Code, whichever is applicable.
2. Apply correct line voltage to the unit. A
7
⁄8" (22mm) or 1
1
⁄8"
(29mm) hole is supplied on the side of the unit. A discon-
nect switch near the unit is required by code. Power to the
unit must be sized correctly and have time delay (dual
element) fuses or an HACR circuit breaker for branch
circuit overcurrent protection. See the nameplate for
correct ratings.
230 Volt operation and 50 cycle units
All 208-230 volt single and three-phase units are factory
wired for 208 volt operation. For 230 volt operation, the line
voltage tap on the 24 volt transformer must be changed.
Disconnect and cap the red lead wire and interchange it with
the orange lead wire on the primary of the 24 volt trans-
former. Three-phase 50 cycle units require a neutral wire for
230/50/1 power.
Fan speed change
All units have two-speed fan motors and are shipped for
high speed operation. On unit sizes 007, 009 and 012, the
change from high speed to low speed is done by removing
the black wire from the fan relay and connecting the red wire
to the fan relay (Figure 4A). On units sizes 015 through 060,
each fan motor is supplied with a 5-pin terminal block
mounted on the fan motor. To change from high speed to
low speed, move the wire from the black #3 location to the
red #4 location on unit sizes 015 through 042 or to the red
#5 location on units sizes 048 and 060. On 575 volt units,
add a jumper between black #3 and blue #4 for low speed
operation. See Figure 4B.
Figure 4A. Figure 4B.
1. All units are recommended to be connected to supply
and return piping in a two-pipe reverse return configura-
tion. A reverse return system is inherently self-balancing
and requires only trim balancing where multiple quanti-
ties of units with different flow and pressure drop char-
acteristics are connected to the same loop. A simple
way to check for proper water balance is to take a
differential temperature reading across the water con-
nections. To insure proper water flow, the differential
should be 10
o
F (5
o
C) to 14
o
F (8
o
C).
A direct return system may also be made to work ac-
ceptably, but proper water flow balancing is more diffi-
cult to achieve and maintain.
2. The piping can be steel, copper or PVC.
3. Supply and return runouts are usually connected to the
unit by short lengths of high pressure flexible hose which
are sound attenuators for both unit operating noise and
hydraulic pumping noise. One end of the hose should
have a swivel fitting to facilitate removal for service. Hard
piping can also be brought directly to the unit although
it is not recommended since no vibration or noise at-
tenuation can be accomplished. The hard piping must
have unions to facilitate unit removal. See Figure 5 for
typical piping setup.
4. Supply and return shutoff valves are required at each
conditioner. The return valve is used for balancing and
should have a “memory stop” so that it can always be
closed off but can only be reopened to the proper
Piping
position for the flow required.
5. No unit should be connected to the supply and return
piping until the water system has been cleaned and
flushed completely. After the cleaning and flushing has
taken place, the initial connection should have all valves
wide open in preparation for water system flushing.
6. Condensate piping can be steel, copper or PVC. Each
unit is supplied with a
7
⁄8" (22mm) ODM copper stub.
7. The condensate disposal piping must have a trap and
the piping must be pitched away from the unit not less
than
1
⁄4" inch per foot (21mm per meter). Generally, the
condensate trap is made of copper and soldered on the
unit. See Figure 6. A piece of vinyl hose from the trap to
the drain line is used for simple removal. A complete
copper or PVC condensate system can also be used.
Union fittings in the copper lines should be applied to
facilitate removal. Factory supplied condensate hose
assemblies have a
7
⁄8" (22mm) sweat to FPT fitting to
facilitate connection of a flexible vinyl, rubber or steel
braided hose.
8. No point in the drain system may be above the drain
connection of any unit.
9. Automatic flow controlled devices must not be installed
prior to system cleaning and flushing.
10. A high point of the piping system must be vented.
11. Check local code for the need for dielectric fittings.
RED (LOW SPEED)
BLACK (HIGH SPEED)
BROWN (CAPACITOR)
COMMON (WHITE)
FAN
MOTOR
FAN
MOTOR
YELLOW 1
BROWN 2
BLACK 3
*RED 4
*RED 5
COMMON
CAPACITOR
HIGH SPEED
LOW SPEED
LOW SPEED
JUMPER
*On unit sizes 048 and 060, terminal 4 is color-
coded blue and terminal 5 is color-coded red.
Page 6 of 24 / IM 407
Figure 5. Figure 6.
Balancing
Valve With
Close-off
Flexible Hose
With Brass
Pipe Fitting
Supply
Return
Condensate
Isolator Pad
Electrical &
Compressor
Access
Blower
Motor
Access
Note: Condensate drain connection must be minimum of 1" (25mm)
below connection to heat pump.
1
⁄4'' Per Foot
(21mm Per Meter)
Optional Cleanout
1
1
⁄2"
(38mm)
1
1
⁄2"
(38mm)
1. Open all valves to full open position and turn on power
to the conditioners.
2. Set thermostat for “Fan Only” operation by selecting
“Off” at the system switch and “On” at the fan switch. If
“Auto” fan operation were selected, the fan would cycle
with the compressor. Check for proper air delivery.
3. All units have two-speed motors. Reconnect for low
speed operation if necessary.
4. Set thermostat to “Cool.” If the thermostat is an auto-
matic changeover type, simply set the cooling tempera-
ture to the coolest position. On manual changeover
types additionally select “Cool” at the system switch.
Start-up
1. Prior to first operation of any conditioner, the water cir-
culating system must be cleaned and flushed of all con-
struction dirt and debris.
If the conditioners are equipped with water shutoff
valves, either electric or pressure operated, the supply
and return runouts must be connected together at each
conditioner location. This will prevent the introduction of
dirt into the unit. Additionally, pressure operated valves
only open when the compressor is operating.
Figure 7.
2. The system should be filled at the city water makeup con-
nection with all air vents open. After filling, vents should be
closed.
The contractor should start main circulator with pres-
sure reducing valve makeup open. Vents should be
checked in sequence to bleed off any trapped air to
assure circulation through all components of the system.
Power to the heat rejector unit should be off, and the
supplementary heat control set at 80
o
F (27
o
C).
While circulating water, the contractor should check
and repair any leaks in the piping. Drains at the lowest
point(s) in the system should be opened for initial flush
and blow-down, making sure city water fill valves are set
to make up water at the same rate. Check the pressure
gauge at pump suction and manually adjust the makeup
to hold the same positive steady pressure both before and
after opening the drain valves. Flush should continue for
at least two hours, or longer if required, to see clear, clean
drain water.
3. Supplemental heater and circulator pump should be shut
off. All drains and vents should be opened to completely
drain down the system. Short circuited supply and return
runouts should now be connected to the conditioner
supply and return connections. Teflon tape is recom-
mended over pipe dope for pipe thread connections. Use
no sealers at the swivel flare connections of hoses.
4. Trisodium phosphate was formerly recommended as a
cleaning agent during flushing. However, many states
and localities ban the introduction of phosphates into
their sewage systems. The current recommendation is to
simply flush longer with warm 80
o
F (27
o
C) water.
5. Refill the system with clean water. Test the litmus paper
for acidity, and treat as required to leave the water slightly
alkaline (pH 7.5 to 8.5). The specified percentage of
antifreeze may also be added at this time. Use commer-
cial grade antifreeze designed for HVAC systems only. Do
not use automotive grade antifreeze.
6. Set the system control and alarm panel heat add setpoint
to 70
o
F (21
o
C) and the heat rejection setpoint to 85
o
F
(29
o
C). Supply power to all motors and start the circulating
pumps. After full flow has been established through all
components including the heat rejector (regardless of
season) and air vented and loop temperatures stabilized,
each of the conditioners will be ready for check, test and
start-up and for air and water balancing.
Cleaning and Flushing System
Note: Do not overtorque fittings. The maximum torque without damage to fittings is 30 foot pounds. If a torque wrench is not available, use as a rule of thumb,
finger-tight plus one quarter turn. Use two wrenches to tighten the union, one to hold the line and one for simultaneous tightening of the nut.
Supply Runout
Return Runout
Mains
Runouts Initially
Connected Together
Rubber Hose
Electrical Access Panel
IM 407 / Page 7 of 24
exceed 35
o
F (19
o
C). If the air temperature exceeds 35
o
F
(19
o
C), the airflow rate is probably inadequate.
If the water temperature difference is less than 6
o
F
(3.3
o
C), the water flow rate is excessive. If the water
temperature difference exceeds 12
o
F (6.7
o
C), then the
water flow rate is inadequate.
6. Check the elevation and cleanliness of the condensate
line. If the air is too dry for sufficient dehumidification,
slowly pour enough water into the condensate pan to
ensure proper drainage.
7. If the conditioner does not operate, the following points
should be checked:
a. Is proper voltage being supplied to the machine?
b. Is the proper type of thermostat being used?
c. Is the wiring to the thermostat correct?
8. If the conditioner operates but stops after a brief period,
check for:
a. Is there proper airflow? Check for dirty filter, incorrect
fan rotation (3-phase fan motors only), or incorrect
ductwork.
b. Is there proper water flow rate within temperature
limits? Check water balancing; backflush unit if dirt
clogged.
9. Check the unit for vibrating refrigerant piping, fan wheels,
etc.
10. Do not lubricate the fan motor during the first year of
operation as it is prelubricated at the factory.
Again, many conditioners have time delays which
protect the compressor against short cycling. After a
few minutes of operation, check the discharge grilles for
cool air delivery. Measure the temperature difference
between entering and leaving water. It should be ap-
proximately 1
1
⁄2 times greater than the heating mode
temperature difference. For example, if the cooling tem-
perature difference is 15
o
F (8
o
C), the heating tempera-
ture difference should have been 12
o
F (5
o
C).
Without automatic flow control valves, a cooling
temperature difference of 10
o
F to 14
o
F (5
o
C to 8
o
C) is
about right. Adjust the combination shutoff/balancing
valve in the return line to a water flow rate which will
result in the 10
o
F to 14
o
F (5
o
C to 8
o
C) difference.
5. Set thermostat to “Heat.” If thermostat is the automatic
changeover type, set system switch to the “Auto” posi-
tion and depress the heat setting to the warmest selec-
tion. Some conditioners have built-in time delays which
prevent the compressor from immediately starting. With
most control schemes, the fan will start immediately.
After a few minutes of compressor operation, check for
warm air delivery at discharge grille. If this is a “cold
building” start-up, leave unit running until return air to
the unit is at least 65
o
F (18
o
C).
Measure the temperature difference between enter-
ing and leaving air and entering and leaving water. With
entering water of 60
o
F to 80
o
F (16
o
C to 27
o
C), leaving
water should be 6
o
F to 12
o
F (3.3
o
C to 6.7
o
C) cooler, and
the air temperature rise through the machine should not
Operating Limits
Environment
This equipment is designed for indoor installation only.
Sheltered locations such as attics, garages, etc., generally
will not provide sufficient protection against extremes in
temperature and/or humidity, and equipment performance,
reliability, and service life may be adversely affected.
Power supply
A voltage variation of ±10% of nameplate utilization voltage
is acceptable. Three-phase system unbalance shall not ex-
ceed 2%.
Operating voltages
115/60/1............................... 104 volts min.; 127 volts max.
208-230/60/1 ....................... 197 volts min.; 253 volts max.
265/60/1............................... 238 volts min.; 292 volts max.
230/50/1............................... 197 volts min.; 253 volts max.
460/60/3............................... 414 volts min.; 506 volts max.
380/50/3............................... 342 volts min.; 418 volts max.
575/60/3............................... 515 volts min.; 632 volts max.
Note: Voltages listed are to show voltage range. However,
units operating with overvoltage and undervoltage for
extended periods of time will experience premature
component failure.
Additional information
1. Standard units — Units are designed to start-up in an
ambient of 40
o
F (5
o
C), with entering air at 40
o
F (5
o
C), with
entering water at 70
o
F (21
o
C), with both air and water at
the flow rates used in the ARI Standard 320-86 rating test,
for initial start-up in winter.
Note: This is not a normal or continuous operating con-
dition. It is assumed that such a start-up is for the purpose
of bringing the building space up to occupancy
temperature.
2. Extended range units — Extended range heat pump
conditioners are designed to start-up in an ambient of
40
o
F (5
o
C), with entering air at 40
o
F (5
o
C), with entering
water at 40
o
F (5
o
C), with both air and water at the flow
rates used in the ARI Standard 320-86 rating test, for initial
start-up in winter.
Note: This is not a normal or continuous operating
condition. It is assumed that such a start-up is for the
purpose of bringing the building space up to occupancy
temperature.
Water enthalpy
Cooling Heating Cooling Heating
Min. Ent. Water
➀ ➁
55
o
F/13
o
C55
o
F/13
o
C40
o
F/5
o
C40
o
F/5
o
C
Normal Ent. Water 85
o
F/29
o
C70
o
F/21
o
C85
o
F/29
o
C70
o
F/21
o
C
Max. Ent. Air,
➀ ➁
110
o
F/43
o
C90
o
F/32
o
C 110
o
F/43
o
C90
o
F/32
o
C
Air and water limits
STANDARD EXTENDED
UNITS RANGE UNITS
Cooling Heating Cooling Heating
Min. Amb. Air 50
o
F/10
o
C50
o
F/10
o
C40
o
F/5
o
C40
o
F/5
o
C
Normal Amb. Air 80
o
F/27
o
C70
o
F/21
o
C80
o
F/27
o
C70
o
F/21
o
C
Max. Amb. Air 100
o
F/38
o
C85
o
F/29
o
C 100
o
F/38
o
C85
o
F/29
o
C
Min. Ent. Air ➀ ➁ 50
o
F/10
o
C50
o
F/10
o
C50
o
F/10
o
C40
o
F/5
o
C
Normal Ent. Air, 80/67
o
F70
o
F 80/67
o
F70
o
F
db/wb 27/19
o
C21
o
C 27/19
o
C21
o
C
Max. Ent. Air, 100/83
o
F80
o
F 100/83
o
F80
o
F
db/wb ➀ ➁ 38/28
o
C27
o
C 38/28
o
C27
o
C
➀ At ARI flow rate
➁ Maximum and minimum values may not be combined. If one value is at
maximum or minimum, the other two conditions may not exceed the
normal condition for standard units. Extended range units may combine
any two maximum or minimum conditions, but not more than two, with all
other conditions being normal conditions.
Page 8 of 24 / IM 407
60 Cycle Wiring Diagrams — Mark IV/AC Units
Figure 8. Unit sizes 007 through 012 (208-230, 265 volts, single-phase) 060686404 Rev. A
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Unit is factory wired for 230V operation. If 230V power supply is
used, transformer must be rewired by disconnecting the power
from the red transformer primary wire and connecting the power
lead to the orange transformer primary wire. Place an insulation
cap on the red transformer primary wire.
3. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
4. All temperature and pressure switches are normally closed.
5. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Unit is factory wired for 230V operation. If 230V power supply is
used, transformer must be rewired by disconnecting the power
from the red transformer primary wire and connecting the power
lead to the orange transformer primary wire. Place an insulation
cap on the red transformer primary wire.
3. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
4. All temperature and pressure switches are normally closed.
5. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
Figure 9. Unit size 015 (208-230, 265 volts, single-phase) 060856804 Rev. A
IM 407 / Page 9 of 24
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Unit is factory wired for 230V operation. If 230V power supply is
used, transformer must be rewired by disconnecting the power
from the red transformer primary wire and connecting the power
lead to the orange transformer primary wire. Place an insulation
cap on the red transformer primary wire.
3. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
4. All temperature and pressure switches are normally closed.
5. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
Figure 10. Unit sizes 019 through 048 (208-230, 265 volts, single-phase) 060686606 Rev. C
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Unit is factory wired for 230V operation. If 230V power supply is
used, transformer must be rewired by disconnecting the power
from the red transformer primary wire and connecting the power
lead to the orange transformer primary wire. Place an insulation
cap on the red transformer primary wire.
3. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
4. All temperature and pressure switches are normally closed.
5. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
Figure 11. Unit sizes 060 (208-230 volts, single-phase) 063393303 Rev. C
Page 10 of 24 / IM 407
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Unit is factory wired for 230V operation. If 230V power supply is
used, transformer must be rewired by disconnecting the power
from the red transformer primary wire and connecting the power
lead to the orange transformer primary wire. Place an insulation
cap on the red transformer primary wire.
3. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
4. All temperature and pressure switches are normally closed.
5. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
Figure 12. Unit sizes 024 through 060 (208-230 volts, three-phase) 060686704 Rev. B
Figure 13. Unit sizes 024 through 060 (460 and 575 volts, three-phase) 060686804 Rev. B
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
3. All temperature and pressure switches are normally closed.
4. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
IM 407 / Page 11 of 24
50 Cycle Wiring Diagrams — Mark IV/AC Units
Figure 14. Unit sizes 007 through 012 (230 volts, single-phase) 061415316 Rev. A
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
3. All temperature and pressure switches are normally closed.
4. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
3. All temperature and pressure switches are normally closed.
4. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
Figure 15. Unit sizes 015 through 019 (230 volts, single-phase) 061415318 Rev. A
Page 12 of 24 / IM 407
Figure 16. Unit sizes 024 (230 volts, single-phase) 061415320 Rev. A
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
3. All temperature and pressure switches are normally closed.
4. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
3. All temperature and pressure switches are normally closed.
4. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
Figure 17. Unit sizes 048 and 060 (230 volts, single-phase) 063393303 Rev. C
IM 407 / Page 13 of 24
Figure 18. Unit sizes 024 through 042 (380 volts, three-phase) 061415321 Rev. A
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
3. All temperature and pressure switches are normally closed.
4. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
Notes:
1. Mark IV/AC controller board contains a static sensitive micropro-
cessor. Proper grounding of field service personnel is required or
damage to controller may result.
2. Terminal block on Mark IV/AC board provides 24 VAC at termi-
nals R and C. All other terminals are 24 VDC output.
3. All temperature and pressure switches are normally closed.
4. Field supplied relays attached to the 24 volt terminals R, W, Y or
G may introduce electrical noise. Never install relays in series
with the inputs.
Figure 19. Unit sizes 048 and 060 (380 volts, three-phase) 061415322 Rev. A
Page 14 of 24 / IM 407
Figure 20. Typical MicroTech 2000 WSHP unit controller single circuit wiring diagram
Notes:
1. Unit is factory wired for 208V operation. If 230V power supply is
used, transformer must be wired by disconnecting the power
lead from the red transformer primary wire. Place an insulation
cap on the red transformer primary wire.
2. All temperature and pressure switches are normally closed.
3. Wires 71 and 72 used only on units with no factory installed
options.
IM 407 / Page 15 of 24
Unit Operation
Figure 28.
INDICATION
LEDS FAULT
YELLOW GREEN RED OUTPUT
Normal mode Off On Off Off
High pressure fault Off Off Flash On
* Low temperature fault Flash Off Off On
Condensate overflow On Dim Off On
Brownout Off Flash Off On
Load shed Off Off On Off
Unoccupied mode On On Off Off
Unit shutdown Off Flash Off On
General
Each unit has a printed circuit board control system. The low
voltage output from the low voltage terminal strip on the
control board is always 24 volts DC (direct current). Termi-
nals R and C on the low voltage terminal strip supply 24 volts
AC power. The unit has been designed for operation with a
24 volt mercury bulb type wall thermostat or a microelec-
tronic wall thermostat selected by the manufacturer. Do not
operate the unit with any other type of wall thermostat.
Two types of units are available: electromechanical con-
trol units or Mark IV/AC control units. Both have 24 volt DC
circuits on the output of the low voltage terminal strip. Each
requires its own unique automatic changeover thermostat.
Mark IV/AC control units
The Mark IV/AC circuit board is an optional control system
with built-in features such as random start, compressor time
delay, night setback, load shed, shutdown, condensate
overflow protection, defrost cycle, brownout, and LED/fault
outputs. Figure 28 shows the LED and fault output se-
quences.
The 24 volt low voltage terminal strip is set up so R-G
energizes the fan, R-Y1 energizes the compressor for cool-
ing operation, R-W1 energizes the compressor and reversing
valve for heating operation. The reversing valve is set up to
be energized in the heating mode. The circuit board has a fan
interlock circuit to energize the fan whenever the compressor
is on if the thermostat logic fails to do so.
The Mark IV/AC control board has a lockout circuit to stop
compressor operation if any one of its safety switches opens
(high pressure switch and low pressure switch on unit sizes
048 and 060). If the low temperature switch opens, the unit
will go into the cooling mode for 60 seconds to defrost any
slush in the water-to-refrigerant heat exchanger. After 60
seconds the compressor is locked out. If the condensate
sensor detects a filled drain pan, the compressor operation
will be suspended only in the cooling mode. The unit is reset
by opening and closing the disconnect switch on the main
power supply to the unit in the event the unit compressor
operation has been suspended due to low temperature
(freezestat) switch, high pressure switch, or low pressure
switch on unit sizes 048 and 060. The unit does not have to
be reset on a condensate overflow detection.
The Mark IV/AC control board has a fault output signal to
an LED on a wall thermostat. Figure 28 shows for which
functions the fault output is “on” (sending a signal to the
LED).
The Mark IV/AC control board has built-in night setback
operation. A “grounded” signal to the “U” terminal on the low
voltage terminal strip puts the unit into the unoccupied mode
for night setback operation. The fan shuts off and the unit is
put under control from the night setback terminal on the
thermostat, W2; day heating and cooling operation is locked
out. R-W2 energizes the compressor and reversing valve for
heating operation. Night setback operation can be overrid-
den for two hours by toggling the fan switch (intermittently
closing the R to O terminals) on the Deluxe Auto Changeover
thermostat. Day thermostat setpoints the control the heating
and cooling operation. The Mark IV/AC control system is also
set up for load shed and shutdown operation on receipt of a
“grounded” signal to the “L” and “E” terminals, respectively,
on the low voltage terminal strip. See Figure 29.
The P and C terminals of the Mark IV/AC board are used
for pump restart. These terminals pass a voltage signal
whenever the unit compressor is turned on. This signal is
detected by a pump restart relay board providing an N.O. or
N.C. set of contacts for heat pump loop circulation pump
control. When used with the Loop Water Controller, the relay
operation accommodates turning off circulation pump con-
trol. When used with the Loop Water Controller, the relay
operation accommodates turning off circulation pumps dur-
ing unoccupied periods with a safety override dependent on,
at minimum, one WSHP's need. The P and C terminals may
be “daisy-chained” between 200 units. See page 19.
To activate the unoccupied mode for units on the same clock schedule, a single wire can be
“daisy-chained” between units and simply grounded through the time clock contacts. The
same system can also be done to activate the load shed and emergency shutdown modes
by running additional wires between units to ground.
Unit #1 Unit #2
Time Clock
Ground
Figure 29.
To
Additional
Units
Unit #3
* In heating mode only.
14-Position Terminal Strip
Pin Designation Description
1CTransformer ground (Ovac)
2RTransformer supply (24vac)
3V-DC power connection
4PPump request output
5A Alarm fault output
6UUnoccupied input
7LLoad shed input
8ERemote shutdown input
9F+DC power connection
10 Y1 Occupied cooling mode input
11 W1 Occupied heating mode input
12 G Fan only input
13 W2 Unoccupied heating mode input
14 O Tenant override input
Mark IV/AC Sequence of
Operation
Page 16 of 24 / IM 407
Read Outputs
Check Timers
Hi
Pres. Sw ?
Brown Out ?
Low Temp Sw ?
Lo Shed ?
N S B ?
Cond. Overflow?
R - W 1 ?
R -Y 1 ?
Stop Comp.
Flash Red LED
Stop Fan
Flash Green LED
Stop Comp.
Htg Mode?
Stop Comp.
Flash Yellow L E D
Stop Comp.
Turn On Red LED
R - W 2 ?
Start Comp.
Cooling Mode
Turn On Yellow LED
Stop Comp.
Reversing Valve On
Time Delay
Start Comp.
Start Comp.
No
No
Yes
No
Yes
No
No
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
General Use and Information
The Mark IV/AC control board is provided with three drive terminals,
R(24vac), F(24vdc), and C(Ovac) that can be used by the end user to
drive the thermostat inputs (G, Y1, W1, and W2) and control inputs
(U, L, E, and O). Any combination of a single board drive terminal (R,
F, or C) may be used to operate the Mark IV/AC boards control or
thermostat inputs. However, only one drive terminal (R, F, or C) can
be connected to any individual input terminal or damage will occur.
Some of the control inputs are used within the Water Source Heat
Pump and not accessible to the end user. For example, HP, LT, and
COF are not available for use by the end user.
Typically the Mark IV/AC board’s R(24vac) terminal is used to drive
the board’s thermostat inputs and control inputs by connecting it to
the R terminal of an industry standard thermostat. The control
outputs of the standard thermostat are then connected to the Mark
IV/AC board thermostat inputs and control inputs as needed. Any
remaining board input(s) may be operated by additional thermostat
outputs or remote relays (dry contacts only).
All Mark IV/AC board inputs must be operated by dry contacts
powered by the control board’s power terminals. No solid state
devices (Triacs) may be used to operate Mark IV/AC board inputs.
No outside power sources may be used to operate Mark IV/AC
board inputs.
Note: The fault output is energized when no faults exist. The fault output is
de-energized during faults and when unit power is off.
Using Drive Using Drive Using Drive
Terminal R (24vac) Terminal F (vdc) Terminal C (ground)
De-energized Energized De-energized Energized De-energized Energized
Place the Meters
Place the Meters Place the Meters Place the Meters
Red (+) Lead on
on Black (-) Lead Black (-) Lead Black (-) Lead
Input to be
on C on V on R
checked
U, L, E, Y1, W1,
10 to 22 to
0vdc
30 to 10 to 22 to
G, W2, O 14vac 26vac
33vdc
14vac 26vac
LED Status and Fault Output Status
Board Status LED’s Fault Output
Mode Yellow Green Red Terminal A
Occupied Off On Off Energized
Unoccupied On On Off Energized
Load Shed Off Off On Energized
Condensate Overflow On Dim Off De-Energized
High/Low Pressure Fault Off Off Flash De-Energized
Low Temperature Fault* Flash Off Off De-Energized
Brownout Off Flash Off De-Energized
Emergency Shutdown Off Flash Off De-Energized
*in heating mode only
Remote Reset of Manual Lockouts – The Remote Reset feature
provides the means to remotely reset automatic lockouts generated
by high-pressure and/or low-temperature (in heating) faults. When
the Mark IV board is in automatic lockout due to one of these faults,
and the cause of the fault condition has been alleviated, energizing
the O-terminal for 10 seconds or more will force the Mark IV board
to clear the lockout. A unit power cycle can also be used to clear an
automatic lockout if the conditions causing the fault have been
alleviated.
Fault Retry To Minimize Nuisance Trips – The Fault Retry feature
helps to minimize nuisance trips of automatic lockouts caused by
high-pressure and/or low-temperature (in heating) faults. This feature
clears faults the first two times they occur within a 24-hour period and
triggers an automatic lockout on the 3rd fault. The retry count is reset
to zero every 24 hours.
IM 407 / Page 17 of 24
Thermostat Connection Diagrams
Mark IV/AC Units – Unit Sizes 007 to 060
Non-Programmable Electronic Thermostat (P/N 668054201)
7-Day Programmable Electronic Thermostat (P/N 107095901)
Includes Thermostat and Wall Plate.
Refer to the installation, operation &
application guide (LIA217) for thermostat
107095901 installation details
Optional Remote Sensor (P/N 667720401)
1. Remove cover from remote sensor housing.
2. Select an appropriate location for mounting the remote
sensor.
3. Mount remote sensor unit using hardware provided.
4. Install two strand shielded wire between remote sensor
and thermostat. Shielded wire must be used.
Do not run remote sensor wire in conduit with other wires.
• Wire 1 should run between the S1 terminal on the
thermostat and the S1 terminal on the remote sensor
• Wire 2 should run between the S2 terminal on the
thermostat and the S2 terminal on the remote sensor
• Connect the shielding of the wire to the S2 terminal on
the thermostat
5. Disable the main sensor (R12) on the thermostat by
cutting it from the circuit board.
S1
S2
S1
S2
Cut R12 from
circuit board
Remote Sensor
Thermostat
Wire 1
Wire 2
WSHP Mark IV/AC Board Low Voltage Terminal Strip (Circuit1)
OW2GW1Y1 F E L U A P V R C
RCW1Y1 W2 Y2 G
Thermostat Terminals
WSHP Mark IV/AC Board Low Voltage Terminal Strip (Circuit1)
OW2GW1Y1 F E L U A P V R C
RCW1Y1 W2 Y2 G O
Thermostat Terminals
Override (Optional)
Includes Thermostat and Wall Plate.
Refer to the installation, operation &
application guide (LIA204-4) for
thermostat 668054201 installation details
Page 18 of 24 / IM 407
Multiple Unit Control Panel for Mark IV
Up to 3 Units (Part No. 056794201)
The multiple unit control board is an accessory used when you
need to control up to 3-units from a single thermostat. The
board is typically mounted in the unit control box closest to the
thermostat. A maximum of 2 boards may be used together if up
to 6-units must be connected and controlled from a single
thermostat.
The multiple unit control board is an accessory used when you
need to control up to 2-units from a single thermostat. The board
is typically mounted in the unit control box closest to the
thermostat. The "G", "W", "Y", "C", and "L" connections are
short flying leads pre-attached to the board. A maximum of 3
boards may be used together if up to 4-units must be connected
and controlled from a single thermostat.
This version of the board uses VDC relays and should not be
OW2GW1Y1 F E L U A P V R C
WSHP Mark IV/AC Board Low Voltage Terminal Strip
OW2GW1Y1 F E L U A P V R C
OW2GW1Y1 F E L U A P V R C
R
Y
G
W
R
Y
G
W
R
Y
G
W
GWYR C
WSHP Mark IV/AC Board Low Voltage Terminal Strip
WSHP Mark IV/AC Board Low Voltage Terminal Strip
Multiple Unit
Control Panel
TB3
TB2
TB1
TB4
RCW1Y1 W2 Y2 G
Thermostat Terminals
This version of the board uses VAC relays and should not be
used in combination with any other accessories or equipment
that require VDC connections to the "G", "W1", or "Y1" terminals
(i.e. Boilerless System Kit).
The multiple unit control board provides the components nec-
essary to protect the Mark IV/AC board from electrical damage
that may occur when using standard off-the-shelf relays.
Up to 2 Units (Part No. 106059801)
used in combination with any other accessories or equipment
that require VAC Connections to the "G", "W1" or "Y1" terminals
(i.e. Boilerless System Kit). Do not use the unoccupied (U-
terminal) feature with the multiple unit control board.
The multiple unit control board provides the components nec-
essary to protect the Mark IV/AC board from electrical damage
that may occur when using standard off-the-shelf relays.
WSHP Mark IV/AC Board Low Voltage Terminal Strip
OW2GW1Y1 F E L U A P V R C
R
Y
G
W
L
Multiple Unit
Control
Panel
WSHP Mark IV/AC Board Low Voltage Terminal Strip
OW2GW1Y1 F E L U A P V R C
GWY C L
RCW1Y1 W2 Y2 G
Thermostat Terminals
IM 407 / Page 19 of 24
WSHP Mark IV/AC Board Low Voltage Terminal Strip
OW2GW1Y1 F E L U A P V R C
1
2
3
Auxiliary Relay
Orange
Yellow
White
WSHP Mark IV/AC Board Low Voltage Terminal Strip
OW2GW1Y1 F E L U A P V R C
1
2
3
Auxiliary Relay
Orange
Yellow
White
Options on Mark IV/AC Units
Motorized Valve & Relay for Unit Sizes 007 to 060
The auxiliary relay is designed to interface external equip-
ment with the Mark IV/AC board. The auxiliary relay has been
provided with the components necessary to protect from
electrical damage that may occur to the Mark IV/AC board
when using standard off-the-self relays. The auxiliary relay
can be used to provide fault signals, unit operation signals,
or to provide a means for remote equipment to control the
Mark IV/AC board. The orange, yellow, and white connec-
tions are short flying leads pre-attached to the board. The
diagrams shown are some connection examples.
Auxilliary Relay (P/N 106059701)
Wired as shown below the motorized valve will open on
a call for compressor operation. Valves for unit sizes
007 to 019 are
1
⁄2" power-open spring-return, while unit
sizes 024 to 060 are
3
⁄4" power-open spring-return.
Other thermostat combinations may be used. Valve and
auxiliary relay are purchased separately.
Note: The wiring shown below can only be used when the “P” terminal
is not being used as a pump restart signal to other equipment. If the
“P” terminal must be used as a pump restart signal to other equipment,
then wire the auxiliary relay’s yellow wire to “Y1”, white wire to “W1”,
and orange wire to “C”, then the valve will open on a call for occupied
heating or cooling from the thermostat.
6
3
1
Black to 6
White to 1
Plug
Pins,
Female
Conduit
Anti-Short
Bushing
Connector
Valve
36" (915 mm)
Lead Length
Operation: In this example the
auxiliary relay contacts can be
used to indicate a fault
condition. With the auxiliary
relay connected as shown, the
normally open contacts will
close during a fault condition.
Operation: In this example the
auxiliary relay contacts can be
used to signal WSHP fan
operation to another device. In
this example when the
thermostat energizes the “G”
terminal the auxiliary relay
normally open contacts will
close.
Operation: In this example the
auxiliary relay is used to
interface other control devices
to the Mark IV/AC board. Using
the Orange (-) and White (+)
wires, and 24vac or 24vdc,
another device could be used
to start and stop the WSHP
heating sequence.
P/N 060977401 - 1/2" Valve Kit
P/N 060977301 - 3/4" Valve Kit
P/N 859004354 - Valve Relay Kit
WSHP Mark IV/AC Board Low Voltage Terminal Strip
OW2GW1Y1 F E L U A P V R C
1
2
3
Auxiliary Relay
Orange
Yellow
White
WSHP Mark IV/AC Board Low Voltage Terminal Strip
OW2GW1Y1 F E L U A P V R C
1
2
3
Auxiliary Relay
Orange
Yellow
White
631
Time Clock
(by others)
Daisy-chain to
additional Mark IV/AC
board “U” terminals
BL
GN
Page 20 of 24 / IM 407
Boilerless System Kit (BSK)
P/N 062522201 for Sizes 007 to 042 & P/N 062522204 for Sizes 048 to 060
The BSK option for use with the Mark IV/AC control board
provides the capability to control a remote duct heater. The
duct heater must be provided with a low voltage control
circuit that only requires a set of dry contacts for operation.
The contacts shown on the Boilerless System board (termi-
nals 1, 2, and 3) are used to control the remote duct heater,
the N.O. contacts will close on a call for duct heater heat.
POT1 provides a means to manually adjust the water tem-
perature setpoint (adjustment range is 43
o
F to 60
o
F). The
The BSK field installed kits include the sheet metal enclosure
with cover, wire harness, boilerless system board, auxiliary
relay, and water temperature sensor. When used, one BSK is
required for each unit. To use the BSK kit you attach the sheet
metal enclosure to the unit as shown, route the 4-wire
harness through knockouts and connect to the Mark IV/AC
board, mount and connect and insulate the water tempera-
ture sensor on the water supply line, and then connect the
duct heater control contacts to the duct heater control
circuit.
9.66
(245 mm)
(007 – 042)
14.50
(368 mm)
(048 – 060)
6.5 (165 mm) (007 – 042)
4.12 (105 mm) (048 – 060)
1.75
(44.5 mm)
If night setback (U-terminal) is used, the duct heater will
respond to the occupied W1 thermostat signal. The load
shed input (L-terminal) cannot be used for other control
functions when being used with the BSK.
The BSK is a DC voltage device, when the BSK is used the
thermostat must be wired for VDC operation.
RD
WSHP Mark IV/AC Board Low Voltage Terminal Strip
1
2
3
Auxiliary Relay
Orange
Yellow
White
12345
RD
BR
WH
OR
OR
WH
WH
YE
GR GR
BK
WH
RD
OR
Normal
Override
Pot 1
Boilerless
System
Board
43 Ohm
4-pin
Plug
Water
Temperature
Sensor
Wire Ends to be Field
Connected to the
Mark IV/AC Board
Signal to remote
duct heater
control circuit
Normal/Override switch provides a means to manually force
electric heat to always be used in place of heat pump heat
when in the override position (default position is normal - heat
pump heat).
When the water temperature drops below the value of POT1,
then the duct heater will be used instead of heat pump heat
on a call for heat from the low voltage thermostat (not
included).
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