Heating and Air Conditioning: Description and Operation

Operation of the A/C system is controlled by three switches which are wired in series and the Powertrain Control Module (PCM). When the operator turns the mode switch to the A/C position, a ground path is completed from the PCM (cavity 27) through the CLOSED dual pressure cut-out switch (circuit C20), thermostatic switch (circuit C21), and A/C switch (circuit C12) to circuit Z1. Circuit Z1 is connected to ground.

The PCM interprets this request and supplies a ground path for the A/C compressor clutch relay on circuit C13. Power for the A/C compressor clutch relay is supplied on circuit A21. This circuit is HOT in the RUN position only and connects from the ignition switch to the relay.

Power for the A21 circuit is supplied on circuit A1. This circuit is protected by a fusible link located near the auxiliary jumper post on the left toe box.

When the PCM grounds circuit C13, contacts in the relay CLOSE connecting circuits A16 and C3. The A16 circuit is a direct battery feed and protected by a fusible link located on near the auxiliary jumper post on the left toe box.

Circuit C3 connects from the relay to the A/C compressor clutch.

The A/C compressor clutch receives this voltage and creates a magnetic field energizing the clutch. Ground for the coil is provided on circuit Z12.

The connector at the A/C compressor has a diode located in it. This diode is used to control the induced voltage resulting from the magnetic field collapsing when the clutch is disengaged. The diode provides a path for the voltage to protect other components and systems.

The A/C compressor clutch relay is also used by the PCM to disengage the compressor in a Wide Open Throttle (W.O.T.) condition.

When the A/C system is in operation the PCM also operates the radiator fans.