Bard QTEC QH303D, Installation Instructions Manual

Manual 2100-435D
Page

16 of 38

LOW VOLTAGE CONNECTIONS

These units use a grounded 24 volt AC low voltage
circuit.

The 

“R”

 terminal is the 

hot

 terminal and the 

“C”

terminal is 

grounded.

“G”

 terminal or pin 6 of P4 is the 

fan input

.

“Y”

 terminal or pin 7 of P4 is the 

compressor input

.

“B”

 terminal or pin 8 of P4 is the 

reversing valve input

.

The reversing valve must be energized for heating
mode.

“R”

 terminal or pin 10 of P4 is 

24 VAC hot

.

“C”

 terminal or pin 11 of P4 is 

24 VAC grounded.

“L”

 terminal or pin 12 of P4 is 

compressor lockout

output

.  This terminal is activated on a high or low

pressure trip by the electronic heat pump control.  This
is a 24 VAC output.

“W2”

 terminal or pin 9 of P4 is 

second stage heat

 (if

equipped).  If the unit is equipped with an optional hot
water coil plenum box the water valve will be connected
to this terminal.

“O1” 

terminal of pin 5 of P4 is the 

ventilation input

.

This terminal energizes any factory installed
ventilation option.

“E”

 terminal or pin 3 of P4 is the 

emergency heat input.

This terminal energizes the emergency heat relay.

NOTE: For total and proper control using DDC, a

total of 7 controlled outputs are required (6 if
no ventilation system is installed).  For proper
system operation under Emergency Heat
conditions where the compressor needs to be
deactivated, the B-W2-E outputs need to be
energized.  Removing the Y (compressor)
signal alone turns the compressor off, but does
not activate the additional circuitry embedded
in the heat pump for proper and complete
operation.

“5”

 terminal or pin 2 of P4 is the 

24 dehumidification

circuit.

“4”

 terminal of pin 4 or P4 is the 

dehumidification

circuit.

.  A contact 

must 

connect terminals 4 and 5.

“6”

 terminal of pin 1 of P4 is 

VAC grounded to the

humidistat

, if needed.

S

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GENERAL

This unit is equipped with a variable speed ECM motor.
The motor is designed to maintain rated airflow up to
the maximum static allowed.

  It is important that the

blower motor plugs are not plugged in or unplugged
while the power is on.  Failure to remove power prior
to unplugging or plugging in the motor could result in
motor failure.

           CAUTION

Do not plug in or unplug blower motor
connectors while the power is on.  Failure to do
so may result in motor failure.