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.

OPERATION
When the ECM 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 ECM gives the system enough time to anticipate idle needs.