Page 1 of 6
Bard Manufacturing Company, Inc.
Bryan, Ohio 43506
www.bardhvac.com
Manual: 7960-860A
Supersedes: 7960-860
Date: 12-9-19
The CMH-34 is a field-installable low ambient fan cycling
control to be used with a Bard wall-mounted heat pump.
The CMH-34 kit is for use with Bard models W24HB,
W30HB and W36HB wall-mount heat pumps.
The CMH-34 kit consists of:
• 7960-860 Supplemental Instructions
• 8406-105 Low Ambient Fan Cycling Switch
• 910-2011 Relay Assembly
• 910-2058 Outdoor Temp Switch Assembly
• 8408-048 Freeze Protect Thermostat
• 1012-065 Phillips Head Screw (2)
• 1012-085 Hex Head Self-Tapping Screw (2)
• 7950-009 Cable Tie (4)
• 7961-312-0516 CMH-34 Unit I.D. Label
Field-supplied tools needed:
• Personal protection equipment, including gloves
and safety glasses
• 5/16" nut driver
• 1/2" wrench (service port) and 9/16" wrench (LAC
control)
• Phillips head screwdriver
CMH-34 Low Ambient Control Kit
SUPPLEMENTAL INSTRUCTIONS
Sharp metallic edges.
Take care and wear appropriate protective
devices to avoid accidental contact with
sharp edges.
Failure to do so can result in personal
injury.
!
CAUTION
Exposed moving parts.
Disconnect all electrical power before
servicing.
Failure to do so can result in severe injury
or amputation.
!
WARNING
Electrical shock hazard.
Disconnect the remote electric power
supply or supplies before servicing.
Failure to do so can result in serious injury
or death.
!
WARNING
Manual 7960-860A
Page 2 of 6
Installation
1. Disconnect all power to the unit.
2. Remove outer and inner control panel covers, upper
front panel and right-side condenser inlet grille.
3. Mount 910-2011 relay assembly to control panel
as shown in Figure 1 on page 3. Use phillips head
screws included with kit to attach relay to control
panel.
4. Remove cover from vertical gray cable duct on
control panel to allow wire harness from installed
relay to route into it (see Figure 1).
NOTE: The unit wiring diagram (included with unit
literature assembly and also located on inner
control panel cover) can be used to wire this
kit. However, the following instructions listed
here provide the necessary connections point-to-
point.
NOTE: If this kit is being installed together with the
outdoor thermostat kit, use the relay assembly
supplied with the thermostat kit. Only the solid
black wire and the multiplier will need used
from the relay assembly in this kit.
5. Locate black wire from the relay assembly and
route through cable duct to defrost control logic
board (see Figure 1). Before connecting this black
wire to the NC fan relay contact on the defrost
logic control board, remove wire that is currently
connected there (on 230V models, it’s the black
outdoor fan motor lead; on 460V models, red/black
wire) and connect that wire to Terminal 3 on the
installed relay.
6. Locate black/white wire from relay assembly and
route through cable duct to defrost control logic
board. Connect black/white wire to C terminal. If
the heat pump is a dehum unit, remove the black/
white wire already connected to the C terminal and
stack it back onto the black/white wire from the
relay assembly.
7. Locate blue wire from relay assembly and route
through cable duct to defrost control logic board.
Connect blue wire to B terminal. Remove blue wire
already connected to B terminal and stack it back
onto the blue wire from the relay assembly.
8. A service port is located on the refrigerant liquid
line just above the liquid line filter drier (mounted
to the outdoor fan shroud). This port is intended
for the application of 8406-105 low ambient fan
cycling switch (see Figure 2 on page 4). Remove
the service cap from this service port and quickly
thread the low ambient fan cycling switch onto
this port. Once snug, use two wrenches to tighten
the switch an additional 1/4 turn (one to hold
the service port and one on the switch). Use soap
bubbles to confirm the seal is completely tight on
this connection.
9. Install outdoor temperature switch assembly to the
fan shroud and route the wires to the control panel
as shown in Figure 2. This switch defeats Balanced
Climate airflow whenthe temperature falls below
50°F to help prevent evaporator freeze up. Refer to
the unit installation manual for more information
on Balanced Climate operation.
10. Install freeze protect thermostat to the evaporator
coil as shown in Figure 3 on page 5. Route the
wires down through the copper bushing and into
the control panel with the blower motor wires.
11. Route the two black leads from the low ambient
fan cycling switch up into the control panel with
the other wires from this compartment, taking
care to route and secure the wires. Use cable
ties included with kit. Route the two black wires
into the cable duct and then out the side of
the cable duct towards the installed 910-2011
relay. Connect these two wires to Terminal 1 and
Terminal 3 of the relay (see Figure 4 on page 6).
12. Find the purple wire not connected to anything
that is tucked in the cable duct (see Figure 1).
Pull it out and connect it to the end of the outdoor
temp switch wire that has an insulated 1/4" quick
connect. Connect the other end of the outdoor
temperature switch to the Y terminal on the defrost
logic board for 1-phase units or on the phase
monitor for 3-phase units. Refer to Figures 1 and 4
and the unit wiring diagram.
13. Connect the freeze protect thermostat wires in
line with the “Y” input signal to the defrost logic
control.
For 1-phase units, connect the end with the 1/4"
quick connect to Y terminal on the defrost logic
control. Connect the other end with the 1/4" tab to
the yellow/white wire coming from the low voltage
terminal strip or to the orange/black wire coming
from the low ambient bypass relay (if equipped)
or to the yellow/black wire in units equipped with
mechanical dehumidification. Refer to the unit
wiring diagram.
For 3-phase units, connect the wire end with the
1/4" quick connect to “Y out” on the phase monitor
and the other end with the 1/4" tab to the yellow/
black wire going to the defrost logic control.
14. Recheck wiring by referring to unit wiring diagram.
15. Apply “This unit equipped with CMH-34 control
module” label to the inside of the inner control
panel cover above the wiring diagram.
16. Replace all panels and covers. This completes the
installation.
17. Turn on power to unit. Check for proper operation
of the unit by referring to Sequence of
Operation.
Manual 7960-860A
Page 3 of 6
Sequence of Operation
Check for proper operation of the unit by energizing in
cooling mode. The condenser fan motor should not run
until the discharge pressure has exceeded 280 PSI.
Should the liquid pressure fall below 180 PSI while
running, the condenser fan motor will de-energize until
the head pressure again builds to 280 PSI. Switch to
heating mode. The condenser fan motor should run
anytime the compressor is running regardless of the
discharge pressure. Run unit through defrost cycle.
The condenser fan motor should de-energize during the
defrost cycle.
FIGURE 1
Unit Control Panel
MIS-4106
MULTIPLIER
RELAY
BLACK/WHITE WIRE TO C
BLACK WIRE TO RELAY
BLUE WIRE TO B
SCREWS
LOW AMBIENT CONTROL
CONNECT OD TEMP. SWITCH TO
TAB FROM MAIN WIRE HARNESS
PURPLE WIRE WITH INSULATED
(TERMINAL #1)
BLACK WIRES FOR LAC
Manual 7960-860A
Page 4 of 6
FIGURE 2
THE BUSHING UP TO
THE CONTROL PANEL
MIS-4107
RUN WIRES THROUGH
SCREWS
PART #1012-085
OUTDOOR TEMP
SWITCH ASSY
PART #910-2058
9/16" WRENCH
1/2" WRENCH
LOW AMBIENT CONTROL
PART #8406-112
Manual 7960-860A
Page 5 of 6
FIGURE 3
Freeze Stat Location and Wire Routing
MIS-4054
USE ONE OF THE MIDDLE
HEADER STUBS TO ATTACH
THE FREEZE STAT TO THE
EVAPORATOR COIL
FREEZE STAT WIRES
RUN DOWN COPPER
THROUGH THE GROMMET
AND INTO THE CONTROL
PANEL WITH THE BLOWER
MOTOR WIRES
Manual 7960-860A
Page 6 of 6
FIGURE 4
Temp
Out Door
Switch
11 1234567891012
Low Ambient Control (opt.)
5
6
2
3
4
1
Low Ambient
Bypass
COM
NC
Sensor
L0
W2
R
C
Y
Defrost Logic
Control
L
B
CC
RV L2 C L1
C
10 AMPS
Y-OUT
18-30 VAC INPUT
Y C
THE USA
MADE IN
ICM
P/N ICM401
8201-085
AE7115
ON FAULT
MAY BE ENERGIZED.
ALL TERMINALS
BEFORE SERVICING.
TURN OFF ALL POWER
SHOCK HAZARD:
FOR 50Hz
CUT WIRE
190-600 VAC
L1, L2, L3,
L1 L2 L3
L1
L2
T1
T2
Compressor
Contactor
MIS-4105 A
OR TO "Y" TERMINAL ON
PURPLE
THE PHASE MONITOR FOR 3-PHASE UNITS.
OUTDOOR TEMP SENSOR TO
VOLTAGE BLOCK)
(BEHIND LOW
MOTOR
BLACK
BLACK
BLUE
YELLOW
BROWN
BLUE
BLACK
BLACK/WHITE
YELLOW
PHASE MONITOR
OUTDOOR FAN
12 PIN PLUG
"Y" TERMINAL ON THE DEFROST
LOGIC BOARD FOR 1-PHASE UNITS,
NOTE:
CONNECT YELLOW WIRE FROM
YELLOW WIRE
FOR 3 -PHASE
UNITS ONLY
-
1
-
2
-
3
-
4
-
5
-
6
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