LS 400 V8-4.0L (1UZ-FE) (1990)
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 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.