Control Module HVAC: Description and Operation

PURPOSE
A/C compressor delay control prevents air conditioning compressor operation for about 0.5 seconds after the system is turned on. The system also momentarily interrupts compressor clutch operation during sudden acceleration of heavy engine loads.

OPERATION
When the ECU detects a request for air conditioning, it uses the ISC motor to raise idle speed before allowing compressor operation. Compressor operation is controlled through the magnetic clutch relay.

Air conditioning typically causes a loss of idle speed and possible momentary engine roughness. The 0.5 second delay imposed by the ECU gives the system enough time to anticipate idle needs.