Compressor Control

To engage compressor clutch, ATC ECU first outputs an A/C request signal to the Engine Control Module (ECM). If ECM agrees that compressor can be engaged, it responds with an A/C signal to ATC ECU. ATC ECU then energizes compressor clutch via dual-pressure switch. Automatic compressor operation is then governed by evaporator temperature sensor input. If output air temperature leaving evaporator decreases to the point where ice may form and restrict airflow, ATC ECU de-energizes compressor clutch until output air temperature leaving evaporator increases. ATC ECU also de-energizes compressor clutch if the A/C OFF switch is pressed, or if ECM withdraws A/C signal because of high engine temperature or high engine load.