8
Marvair ComPac Installation & Operation Manual
12/2017 Rev.16
allowing the contactor to energize. The delay can be adjusted by the DOM wheel on the board. Factory
recommended wait is 3 minutes.
Low Pressure By-Pass Time
When starting, the low pressure switch (LPS) fault condition will be by-passed for 3 minutes before the
contactor is de-energized.
Post Purge
Upon a call for indoor airflow “G” the blower will energize immediately. When in the cooling mode, the
blower will remain energized for 10 to 90 seconds (adjustable) after the compressor has been de-energized.
The time period can be changed by fan purge wheel on the board. Factory setting is 90 seconds.
LED Indicator Lights
COLOR
TYPE
STATUS
DESCRIPTION
Green
Power
Constant On
24 VAC power has been applied
Red
Status
Constant On
Normal operation
Red
Status
1 Blink
High pressure switch has opened twice
Red
Status
2 Blinks
Low pressure switch has opened twice
Low Ambient Control
The low ambient control permits 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 290 PSIG. Therefore, the outdoor fan always starts
after the compressor, and
it will cycle frequently during normal operation at low outdoor conditions.
High Pressure Switch
The high pressure switch is mounted on the liquid line. It is electrically connected to a lockout circuit
on the board which shuts down the system if the refrigerant pressure rises to 650 PSIG. This protects the
unit if airflow through the condenser is blocked or if the outdoor fan motor fails.
Although the contacts of the high pressure switch close when the refrigerant pressure falls to approximately
450 PSIG, the system must be manually reset once the lockout circuit is activated. A manual reset is
necessary to prevent harmful short-cycling. To reset switch, turn primary power off, then back on or turn
thermostat system switch off, then back on.
Low Pressure Switch
The low pressure switch is mounted on the compressor suction line. It is designed to open if the refrigerant
pressure drops to 40 PSIG; it resets when the pressure rises to 60 PSIG. The switch protects the unit if
airflow through the indoor blower is impeded, if the blower motor fails, or if there is a loss of refrigerant.
