Roadmaster Estate Wagon V8-350 5.7L VIN P SFI (1996)
A/C Signal: Description and Operation
AC Clutch Circuit
DESCRIPTION
In order to improve engine operation, and protect the A/C compressor and A/C clutch during Wide Open Throttle (WOT) performance, the A/C
compressor operation is controlled by the PCM.
This A/C system consists of the following components:
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The heater and A/C control
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The A/C pressure cycling switch
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The A/C refrigerant pressure sensor
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The A/C clutch relay
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The A/C compressor clutch
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The PCM.
OPERATION
The A/C refrigerant pressure cycling switch is closed when there is sufficient system pressure (depending on refrigerant charge and ambient
temperature). When the heater and A/C control is placed in the A/C mode, a request signal is sent to the PCM. The PCM will then energize the
A/C clutch relay, unless abnormally high or low A/C pressure is detected by the A/C refrigerant pressure sensor. The PCM will also turn the
cooling fans ON when A/C is requested. The A/C clutch relay is controlled by the PCM so that the PCM can increase idle speed before turning
ON the clutch or disable the clutch during WOT, or high coolant temperature.
The PCM will energize the A/C clutch whenever the engine is running less than 4100 RPM and A/C has been requested, unless any of the
following conditions are met:
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Wide Open Throttle (WOT).
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A/C head pressure greater than 431 psi or less than 0 psi (as determined by the A/C refrigerant pressure sensor).
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Ignition voltage less than 10 volts.
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Engine speed greater than 5550 RPM for 189 seconds.
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ECT greater than 124°C (256°F). The A/C Request Table should be used for diagnosing the A/C request circuit only. Refer to Heating and
Air Conditioning to diagnose the refrigerant portion of the system.
SCAN TOOL DIAGNOSIS
The scan tool will be used in diagnosing the system. The PCM has the ability to display the following parameters:
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A/C request input to the PCM
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A/C compressor status
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A/C system pressure
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A/C clutch ON or OFF status
Refer to Heating and Air Conditioning to diagnose the refrigerant portion of the system.