Compressor Clutch Does Not Engage

HVAC COMPRESSOR CLUTCH DOES NOT ENGAGE

DIAGNOSTIC AIDS
The A/C compressor clutch will not engage under the following conditions:
- The A/C high side line pressure is over 2957 kPa (429 psi).
- The A/C low side line pressure is under 151 kPa (22 psi).
- The throttle angle is at 100 percent.
- The engine speed is more than 5,500 RPM.
- The engine coolant temperature (ECT) is more than 121°C (250°F).
- The ambient air temperature (AAT) is less than 5°C (40°F).
- The engine is idling at a low unstable RPM.

Compressor clutch engagement cannot be used to determine the status of the low pressure switch. The low pressure switch is one of several inputs to the HVAC control module for A/C request authorization. A/C request is one of several inputs to the powertrain control module (PCM) that control A/C compressor clutch engagement.

Using a scan tool to monitor low pressure switch status while monitoring the low side pressure with the ACR 2000 at the service port and watch the pressure at which the switch opens/closes is imperative to successfully diagnosing the switch.

TEST DESCRIPTION

Steps 1-2:

Steps 3-5:

Steps 6-7:

Steps 8-11:

Steps 12-15:

Steps 16-19:

Steps 20-24:

Steps 25-31:

Steps 32-35:

The numbers below refer to the step numbers on the diagnostic table.
2. The A/C compressor output is disabled if the engine is idling at a low unstable RPM.
3. The A/C compressor relay output is disabled if ECT is above 121°C (250°F). The Engine Coolant indicator will illuminate at this temperature.
4. This step ensures that the HVAC control module is receiving an input from the A/C switch.
5. These actions will enable the A/C compressor to operate.
6. This test ensures that there is sufficient refrigerant in the A/C system. The specific values come from the A/C System Performance Test in Heating, Ventilation and Air Conditioning.
8. The A/C low pressure switch parameter is out of range when the HVAC control module interprets the signal being below 151 kPa (22 psi).
9. This action will simulate a closed switch condition. If the Pressure Cycle Switch parameter reads Low Pressure than there is a circuit condition or a condition with the HVAC control module.
12. The A/C compressor relay output from the PCM is disabled if the A/C high side system pressure is interpreted to be higher than 2958 kPa (429 psi).