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Home >> Ford >> 1997 >> Mustang V6-3.8L VIN 4 >> Repair and Diagnosis >> Heating and Air Conditioning >> Description and Operation >> Electrical System
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Electrical System

The electrical system consists of the following components:
- Blower motor
- heater blower motor switch
- A/C-heater function selector switch
- 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 (CCRM)
- Powertrain Control Module (PCM)
- Fuses and wiring to complete the circuit

The blower motor is installed in the A/C evaporator case.

The heater blower motor switch:
- is mounted on the A/C control assembly.
- with the heater blower motor switch resistor, allows the selection of four A/C blower motor speeds.

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

The Constant Control Relay Module controls A/C clutch and engine cooling fan motor operation based on signal received from the A/C cycling switch, the A/C pressure cut-off switch and the PCM.
- 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 constant control relay module deactivates the A/C clutch when signalled by the powertrain control module. The A/C clutch could be deactivated in this manner under the following conditions:
- engine start-up
- Wide Open Throttle (WOT)
- during low engine idle conditions
- excessively high engine temperature

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