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ComPac 9/04-12
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 250 PSIG. The switch opens again when the refrigerant pressure falls to 190
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 compressor discharge line. It is electrically
connected to a lockout relay which shuts down the system if the refrigerant pressure rises to
400 PSIG (AVP60 setting is 450 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 300 PSIG, the system must be manually reset once the lockout relay 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 35 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.
LEDs
POST PURGE
WHEEL
DELAY ON MAKE
(COMPRESSOR TIME DELAY)
WHEEL
MOVE WIRE FROM NORMALLY OPEN TERMINAL TO
NORMALLY CLOSED IF NORMALLY CLOSED IS DESIRED
