Compressor Clutch Relay: Description and Operation

Air Conditioning:

SYSTEM OPERATION
When the air conditioner switch is turned on, while the engine is at idle, the Idle Speed Control (ISC) servo operates to increase the engine speed. However, there is some delay before the engine speed actually increases. To maintain the engine free from the air conditioner load during that delay period, the ECU keeps the power off for about 0.5 seconds. As a result, even if the air conditioner switch is on, the air compressor is not driven instantly, preventing engine speed drop due to compressor load. In addition, for automatic transmission equipped models, during acceleration when the throttle valve opening is above 65°, the air conditioner power relay circuit is shut off for approximately five seconds. This improves engine acceleration performance.

A/C Relay:

RELAY OPERATION
The relay, located in the in front of the drivers left knee bolster, is an electromechanical 1 make relay. The ECU monitors the A/C on signal from the switch to the relay. When positive voltage is supplied from the switch to the relay coil, the ECU supplies the ground circuit to the relay coil (if conditions are suitable). This energizes the relay, causing the contacts to close. Positive battery voltage flows through the contacts to the compressor clutch, energizing it.