A/C Compressor Clutch

With the engine running, 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 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.