Product manual
11
ComPac 6/09-18
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 refrig-
erant 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 airow 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 approxi-
mately 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 re-
frigerant pressure drops to 35 PSIG; it resets when the pressure rises to 60 PSIG. The switch protects
the unit if airow 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