A/C Clutch Circuit Operation

A/C Clutch Circuit Operation
A 12-volt signal is supplied to the A/C request input of the PCM when the A/C is selected through the A/C control switch.

The A/C compressor clutch relay is controlled through the PCM. This allows the PCM to modify the idle air control position prior to the A/C clutch engagement for better idle quality. If the engine operating conditions are within their specified calibrated acceptable ranges, the PCM will enable the A/C compressor relay. This is done by providing a ground path for the A/C relay coil within the PCM. When the A/C compressor relay is enabled, battery voltage is supplied to the compressor clutch coil.

The PCM will enable the A/C compressor clutch to engage whenever the engine is running and the A/C has been requested. The PCM will not enable the A/C compressor clutch if any of the following conditions are present:
- The throttle opening is greater than 90 %.
- The ignition voltage is below 10.5 volts.
- The engine speed is greater than 6315 RPM.
- The ECT is greater than 119 °C (246 °F).
- The IAT is less than 5 °C (41 °F).
- The power steering pressure switch signals a full lock position of the steering linkage.

How The Circuit Works
With the ignition in ON, battery voltage is applied to the A/C switch, the A/C triple pressure switch (A/T) or A/C dual pressure switch (M/T), the coil of the A/C compressor relay, the contacts of the thermo switch relay and the air selector knob. When you press the A/C switch, battery voltage is applied to the electronic thermostat. The solid-state switch in the electronic thermostat closes, providing a path to ground for the thermo switch relay, with the fan control switch in any position except OFF. Voltage is also applied through the A/C triple pressure switch (A/T) or the A/C dual pressure switch (M/T) to the coil of the thermo switch relay. This closes the thermo switch relay contacts, applying battery voltage to the A/C ON input of the engine or powertrain control module (ECM or PCM). The ECM or PCM then provides ground for the A/C compressor relay. The A/C compressor relay contacts close, applying battery voltage to the compressor clutch. If the A/C triple pressure switch (A/T)/dual pressure switch (M/T) opens, the compressor clutch disengages.