A/C Request Signal
This signal indicates to the PCM, that an A/C mode is selected at the A/C controller. The PCM uses this information to adjust the idle speed before turning on the A/C clutch. If this signal is not available to the PCM, the A/C compressor will be inoperative.
The A/C Request Signal is a battery positive voltage that is supplied to the PCM when the A/C control is activated or when the Heater- A/C control mode selector is placed in any of the following modes:
| • | MAX A/C |
| • | NORM A/C |
| • | BI-LEVEL |
| • | DEFOG |
| • | DEFROST |
Under normal operating conditions, the following actions occur:
- The PCM supplies a ground to the relay coil of the A/C compressor control.
- The relay energizes.
- Voltage is supplied to the A/C compressor clutch through the relay center fuse.
- The A/C compressor clutch engages.
- The compressor runs.
If the PCM determines that the engine load should be reduced, such as during full throttle conditions, the PCM de-energizes the relay of the A/C compressor control in order to disengage the compressor clutch. The de-energization occurs even though the voltage signal from the heater and A/C control is still present at the PCM.
A/C Refrigerant Pressure Sensor
The electronic A/C refrigerant pressure sensor is mounted to the line between the condenser and the evaporator. The output to the PCM is variable and depends on the pressure inside the line. A higher pressure will result in a higher voltage out.
The PCM constantly monitors the A/C system pressure in order to achieve the following effects:
| • | Disengage the A/C clutch if the pressure is above 2700 kPa (440 psi). |
| • | Disengage the A/C clutch if pressure is below 285 kPa (38 psi). |
| • | Boost the idle air control in order to compensate for the A/C load at idle. |
| • | Control the cooling fan operation. |
A fault in the A/C refrigerant pressure sensor signal will cause DTC P0530 to set.
The Air Conditioning (A/C) Compressor Control Circuit Diagnosis should be used for diagnosing the electrical portion of the A/C compressor clutch circuit. When diagnosing the refrigerant portion of the HVAC system, the Cooling Insufficient - Air Conditioning (A/C) System in HVAC should be used.
A scan tool will be used in diagnosing the system. The scan tool has the ability to read the A/C request and refrigerant pressure inputs to the PCM. The scan tool can display when the PCM has commanded the A/C clutch on. The scan tool should have the ability to override the A/C request signal and energize the A/C control relay.
