Circuit Operation

CIRCUIT OPERATION
A/C Operation
When the A/C switch is CLOSED or the Defrost switch is moved to the ON position, and the evaporator temperature is in the normal limits, the Body Control Module (BCM) sends a signal to the Powertrain Control Module (PCM), over 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 attached 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 the F18 circuit. The F15 circuit is protected by a 10 Amp fuse located in cavity 9 of the Power Distribution Center (PDC).

When the coil is energized contacts in the relay CLOSE connecting circuits A16 and C3. Circuit A16 is protected by a 40 Amp fuse located in cavity 17 of the PDC and also supplies power for the radiator fan relays. The C3 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.

A/C Heater Control
The air conditioning-heater system is controlled by the Body Control Module (BCM). The BCM senses voltage of the A/C-Heater control on circuit C58. The control uses resistors to internal to the control. These resistors are connected to the Z2 ground circuit.

When the operator requests a function in the system the BCM measures the voltage, on circuit C58, and activates the mode actuator door to the proper position.

A separate A/C switch is used in the system. This switch works the same as the mode actuator switches. when the operator presses the switch the BCM measures the voltage on the C21 circuit and activates the proper functions. Internal to the A/C-Heater control the A/C switch is connected to the blower motor switch. This allows the A/C system to only operate when the blower switch in an ON position.

Ground for the A/C switch is provided through the blower motor switch to the Z1 circuit. This circuit terminates at the instrument panel ground. A Light Emitting Diode (LED) is connected in the C21 circuit and illuminates when the A/C system is operating.

Illumination lamps and LED's are internal to the control. These are controlled by the BCM. The E2 circuit from the BCM provides the voltage to the control for lamp and LED illumination. Ground for the lamps and LED's is provided on the Z1 circuit which terminates at the instrument panel left side cowl.