A/C Signal: Description and Operation

Fuel Pump Relay:

PURPOSE
In order to improve idle quality, wide open throttle performance, and to protect the system, the A/C compressor is controlled by the Powertrain Control Module (PCM).

This system uses a variable displacement compressor, referred to as the V-5 type compressor. The V-5 type meets A/C requirements without cycling. For a description of the system and an explanation of the components used, refer to Heating and Air Conditioning.

OPERATION
This system consists of an A/C select switch, an Instrument Panel Cluster (IPC) clutch, a control relay and the compressor clutch in a series circuit. An A/C refrigerant pressure sensor is also used to indicate high side pressure to the PCM for use in determining cooling fan, A/C compressor and idle speed control. A fault in the A/C refrigerant pressure sensor circuit should set a Diagnostic Trouble Code (DTC) 66, which will cause the PCM to disable the A/C compressor.

The A/C refrigerant pressure sensor also provides low and high pressure protection for the system. If the A/C refrigerant pressure sensor signal exceeds about 4.92 volts, indicating pressure of about 3189 kPa (462 psi) with A/C "ON" or 3.98 volts indicating pressure of 2634 kPa (382 psi) with A/C "OFF," the clutch will disable. It will remain disabled until A/C refrigerant pressure sensor signal voltage falls below 1.98 volts, indicating 1172 kPa (170 psi). This protects the system from overpressure.

If the A/C refrigerant pressure sensor voltage is less than about 0.19 volt, indicating about 296 kPa (43 psi) the clutch will disable. It will remain disabled until the A/C refrigerant pressure sensor voltage signal rises above about 0.72 volt, indicating about 359 kPa (52 psi). This protects the system in case of loss of freon and prevents the compressor from operating in cold weather.

The A/C refrigerant control relay is controlled by the PCM so the PCM can increase idle speed before enabling the clutch and can disable the clutch during Wide Open Throttle (WOT), high RPM or during hot engine restarts. A/C is also disabled if coolant temperature exceeds 125°C. See Chart C-10 for specific wiring, circuit and calibration description. Chart C-10 A/C Clutch Control Circuit Diagnosis
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