Bard CMH-34 Supplemental Instructions

Brand: Bard

Model: CMH-34

Type: Supplemental Instructions

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.)

Low Ambient

Bypass

COM

Sensor

Defrost Logic

Control

RV L2 C L1

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

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

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

Bard CMH-34 Supplemental Instructions

Bard CMH-34 Supplemental Instructions

Bard CMH-34 Supplemental Instructions

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