Relays and Switches
Low-Pressure Cut-Off SwitchCompressor protection is provided on some cars by a low-pressure cut-off switch which will open in the event of a low-charge condition. This switch also provides low temperature protection.
Compressor Control Relay
The compressor clutch coil is energized through the compressor control relay. This relay is activated by the powertrain control module in A/C modes. The Powertrain Control Module (PCM) provides cut-off of the relay under certain operating conditions such as wide open throttle.
A/C Pressure Sensor
An electronic A/C pressure sensor is mounted to the line (between the condenser and the evaporator). The output to the powertrain control module is variable and is dependent upon pressure inside the line. A higher pressure results in a higher voltage out. The powertrain control module constantly monitors A/C system pressure to:
1. Disengage the A/C clutch if the pressures are too high, 2700 kPa (440 psi).
2. Disengage the A/C clutch if pressures are too low, below 285 kPa (38 psi).
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 he replaced.