Bard CMH-29 Installation Instruction

INSTALLATION INSTRUCTIONS

CMH-29

Low Ambient Control and

Compressor Cutout Thermostat Kit

For Use with W18HA, W24HA, W30HA and W36HA

Wall-Mount Heat Pumps

The CMH-29 is a field-installable combination of low
ambient fan cycling control and a compressor cutout
outdoor thermostat to be used with a Bard wall­mounted heat pump.

The CMH-29 kit consists of:

• 8406-112 Low Ambient Fan Cycling Switch

• 910-2013 Relay and Compressor Cutout
Thermostat Assembly

• 3/8" vinyl-covered clamps

• Required fasteners

• 7960-771 Installation Instructions

The CMH-29 kit is for use with Bard models W18HA,
W24HA, W30HA and W36HA wall-mount heat pumps.

Compressor Cutout Thermostat

Heat pump compressor operation at outdoor
temperatures below 0° is neither desirable nor
advantageous in terms of efficiency. An outdoor
thermostat can be applied to take the mechanical
heating (compressor) offline, and send the (compressor)
signal to energize electric heat in its place (to make
electric heat first stage heating). This can also be
applied to limit the quantity of available electric heat.

Example: Heat pump with 10KW second stage heat.
Once the outdoor thermostat has switched, 15KW
without compressor.

INSTALLATION

1. Disconnect all power to wall-mount unit.

2. Remove outer and inner control panel covers.

3. Remove right side condenser inlet grille.

4. Remove all three front service panels.

5. Mount 910-2013 relay assembly into unit control
panel as shown in Figure 1 on page 3. Use phillips
head screws included with kit to attach relay to
control panel.

6. 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 point­by-point.

Bard Manufacturing Company, Inc.
Bryan, Ohio 43506

www.bardhvac.com

Manual: 7960-771
Supersedes: NEW
Date: 4-14-16

Page 1 of 5

7. Locate yellow/white wire that runs from the 12-pin
plug on the top of the low voltage box to:

• Defrost logic control board on 1 phase non-

dehum models

• Phase monitor on 3 phase non-dehum models

• Dehum logic control board on all dehum

models

Remove from its original position and plug into

yellow/white wire from the 910-2013 relay
assembly installed in Step 5. Locate orange/black
wire from the 910-2013 relay and connect where
yellow/white wire was removed.

8.

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 control logic
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.

9.

Locate black/white wire from relay assembly and
route through cable duct to defrost control logic
board. Connect the wire to the C terminal. If the heat
pump is a dehum unit, remove the black/white wire
already connected to C terminal and stack it back
onto the black/white wire from the relay assembly.

10. Locate blue wire from relay assembly and route
through cable duct to defrost control logic board.
Connect to B terminal. Remove blue wire already
connected to B terminal and stack it back onto the
blue wire from the relay assembly.

11. Locate brown wire from relay assembly and route
through cable duct to defrost control logic board.
Connect to W2 terminal. Remove brown wire
already connected to W2 terminal and stack it back
onto the brown wire from the relay assembly.

12. Route orange/black, yellow/brown and brown
wires up the cable duct in the control panel.
After removing the permagum from around the
blower motor wires, route the wires into the blower
compartment and replace the permagum around all
the wires (see Figures 1 and 2 on pages 3 and 4).

13. Locate the outdoor thermostat shipped in the CMH­29 kit along with two (2) phillips head screws. Use
the two screws to attach the outdoor thermostat
onto the side of the control panel adjacent to the
indoor blower in the blower compartment (see
Figure 2).

14. Carefully unroll the capillary tube and sensing bulb
of the outdoor thermostat, and route it into the
condenser section through the tubing grommet in
the condenser partition. Secure the capillary tubing
to the insulated suction line with the supplied cable
tie.

15. Continue routing the outdoor thermostat bulb within
the condenser section as shown in Figure 3 on page

5. Secure the bulb as per the drawing using the
vinyl-covered clamps and hex head screws included
in the kit. Dress the capillary tube to ensure no
tube-rubs occur and secure with supplied cable ties
in both the condenser and ventilation sections.

16. Connect the orange/black wire to outdoor
thermostat Terminal #1, the yellow/brown wire to
Terminal #2 and the brown wire to Terminal #3.

17. 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 8406-112 low ambient fan
cycling switch (see Figure 3 on page 5). 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.

18. 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 910-2013 relay. Connect
these two wires to Terminal 1 and Terminal 3 of the
relay.

19. Verify outdoor thermostat setpoint. Factory default
is 10°F.

20. Recheck all wiring. Turn on power to unit. 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
350 PSI. Should the liquid pressure fall below 225
PSI while running, the condenser fan motor will
de-energize until the head pressure again builds to
350 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.

21. Apply “This unit is equipped with CMH-29 control
module” label to the inside of the inner control
panel cover above the unit wiring diagram.

22. Re-install all three front service panels.

23. Re-install right side condenser inlet grille.

24. Re-install electrical cable duct cover.

25. Re-install inner and outer control panel covers.

26. Restore unit power.

Manual 7960-771
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