13
Marvair Classic AVPA/HVPA/HVPSA Heat Pump I&O Manual
11/2017 Rev. 7
O
The “O” terminal is the reversing valve input from the thermostat. When there is a 24 VAC signal
present at the “O” terminal, the control will energize the reversing valve through the “RV” terminals. The
control will also energize the “RV” terminals in heat mode during a defrost cycle.
G
The “G” terminal is the indoor blower input from the thermostat. When there is a 24 VAC signal present
at the “G” terminal, the control will energize the indoor blower. When the signal at the “G” terminal is
removed, the fan will remain energized for the pot settable 10-90 second post purge period. When the
damper relay option is selected by placing the jumper in the “Yes” position, the control will energize the
DRO terminal with every “G” call to open the damper. When the “G” call is not present, the control will
energize the DRC terminal to close the damper. The default setting for the damper relay option is “No”.
HPS
High Pressure switch terminals are the high pressure switch input.
LPS
Loss of Charge switch terminals are the loss of charge switch input.
DS
The DS terminals are the defrost sensor input.
CS
The CS terminals are the coil sensor (optional) input. This input will monitor the condenser coil
temperature to allow the head pressure control to modulate the speed of the fan and maintain a constant
head pressure.
Red Status LED
Damper Open/Damper Close
S-Circuit
Electric Heat During Defrost
Test
Defrost Time Delay
(30-60-90 Minutes)
Green Power LED
Delay on Make Pot
Indoor Blower Speed Control Pot
Post Purge Pot
FS DS CS
Indoor Fan
Line 1
Line 2
Condenser Fan
Line 1
Line 2
1
NC
1
COM
1
NO
DRC
DRO
EH
RV
CC
HPS Y LPS W2 O G
1
Contacts
for Remote
Alarms
Figure 1 - PC Control Board
1.7 Options
Low Ambient Control
The low ambient control permits mechanical cooling when outdoor ambient temperatures are low. The
control uses a reverse-acting high pressure switch to cycle the condenser fan motor according to liquid
refrigerant pressure conditions. Switch closure and fan operation occurs when the pressure reaches 400
PSIG. The switch opens again when the refrigerant pressure falls to 245 PSIG. Therefore, the outdoor
fan always starts after the compressor,
and it will cycle frequently during normal operation at low
outdoor conditions.
