Electrical System

The manual A/C-heater electrical system consists of the following components:
^ blower motor
^ heater blower motor switch
^ A/C-heater function selector switch which is serviced as part of the integrated control panel
^ heater blower motor switch resistor with a thermal limiter
^ A/C pressure cut-off switch
^ A/C cycling switch
^ A/C clutch
^ constant control relay module
^ Powertrain Control Module (PCM)
^ fuses and wiring to complete the circuit

The blower motor is installed in the heater blower motor housing, which is part of the A/C evaporator housing.

The heater blower motor switch:
^ is mounted on the integrated control panel.
^ with the heater blower motor switch resistor, allows the selection of four blower motor speeds.

The heater blower motor switch resistor:
^ is installed in the A/C evaporator housing.
^ contains a thermal limiter which is used as a temperature protecting fuse.

The constant control relay module controls A/C compressor and fan motor operation based on information received from the A/C cycling switch, the A/C pressure cut-off switch and the powertrain control module.

^ The A/C cycling switch and A/C pressure cut-off switch are connected in series.
^ The A/C cycling switch is mounted on the suction accumulator/drier.
^ The A/C pressure cut-off switch is mounted to the A/C manifold and tube.
^ The A/C cycling switch closes when the pressure on the low side of the refrigerant system rises to approximately 276-324 kPa (40-47 psi). The constant control relay module will then engage the A/C clutch.
^ The A/C cycling switch will open when the system pressure drops to approximately 152-193 kPa (22-28 psi), disengaging the A/C clutch.
^ In ambient temperatures below approximately 7-10°C (45-50°F), the A/C cycling switch will not allow compressor operation because of low system pressures.
^ The A/C pressure cut-off switch is used on all vehicles to interrupt A/C compressor operation in the event of high system discharge pressures.
^ When compressor head pressure rises to approximately 2896 kPa (420 psi), the contacts open and the constant control relay module will disengage the A/C clutch.
^ When head pressure drops to approximately 1724 kPa (250 psi), the contacts again close and allow operation of the A/C clutch.

The switch contains a second set of electrical contacts for the fan motor which are normally open.

^ When discharge line pressure reaches approximately 2241 kPa (325 psi), these contacts close and the constant control relay module will engage the fan motor.
^ When pressure drops to approximately 1896 kPa (275 psi), the contacts again open and the fan motor is disengaged.