This circuit protects the compressor from low refrigerant charge. It also prevents compressor operation when cab temperature is very low. Does not affect Fan or Heat modes.
A Low Pressure Cutout (LPCO) switch is installed on the evaporator outlet tube. It measures air conditioning system low side (suction) pressure.
LPCO Switch: Open = 5 psig (34 kPa) Close = 20 psig (138 kPa)
If the base controller senses the LPCO switch is open the 7CL (J5 pin 2) output circuit will be turned off and the compressor clutch will disengage. The Evaporator Fan will continue on. The Base controller will delay 60 seconds before checking the position of the LPCO switch. If the LPCO switch is closed the compressor will restart. If the LPCO switch is still open a new 60 second delay will begin.
Check: When alarm code 93 Check Low Pressure Cutout has been logged 3 times within 60 minutes this alarm is set as Check alarm (meaning a yellow triangle on your control module inside cab). Further air conditioning function is disabled.