Relays and Switches

A/C Compressor Control Relay

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.

A/C Pressure Sensor

An electronic A/C pressure sensor is mounted in the line (between the compressor and the condenser). Its output to the PCM is variable and is dependent upon pressure inside the line. A higher pressure results in a higher voltage output. The PCM constantly monitors A/C system pressure to:

1. Disengage the A/C clutch if the pressures are too high.
2. Disengage the A/C clutch if pressures are too low.
3. Boost idle air control to compensate for A/C load at idle.
4. Control cooling fan operation.

The pressure sensor is not repairable, if it fails, it must be replaced.