Compressor Clutch Relay: Description and Operation

The A/C compressor control relay is designed to disengage the A/C compressor clutch momentarily during start-up on a warm engine. The relay is PCM controlled. Voltage is supplied from the A/C power feed circuit and the PCM completes the ground to close a set of normally opened points.
This turns the compressor clutch ON. The PCM opens the ground circuit when an engine run signal is sensed with coolant temperature at a specified amount.

On a warm engine start-up, a time delay of about 3 seconds allows the engine speed to stabilize before the compressor engages.