Manual A/C-Heater

When the A/C switch is CLOSED, or the Defrost switch is in the ON position, a signal is sent from the A/C-Heater control to the Body Control Module (BCM) on circuit C21.

The BCM then looks at the evaporator temperature sensor, located in the A/C-Heater housing. The BCM uses circuit C12 to send a signal to the evaporator sensor and circuit C57 as the sensor return to the BCM.

If the evaporator temperature is in the normal limits the BCM sends a signal to the Powertrain Control Module (PCM), across the CCD Bus, requesting A/C operation.

After receiving this input, the PCM activates the A/C compressor by grounding the C28 circuit, which is connected to the coil side of the A/C clutch relay. This relay is located in the Power Distribution Center (PDC).

Power for the coil side of the relay is supplied on circuit F18. This circuit is protected by a 10 Amp fuse located in cavity 20 of the junction block. The fuse in HOT in the RUN position only

When the coil is energized contacts in the relay close connecting circuits A16 and C2. Circuit A16 is protected by a 40 Amp fuse located in cavity D of the PDC and also supplies power for the radiator fan relays. The C2 circuit connects from the relay to the A/C compressor clutch.

The A/C compressor clutch receives this current and creates a magnetic field, energizing the clutch. The A/C compressor clutch is case grounded to the A/C compressor.

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