Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2004 Oldsmobile Bravada, 2004 GMC Envoy XUV, 2004 GMC Envoy XL, 2004 GMC Envoy, and 2004 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

The A/C compressor is protected from overheating by the compressor temperature switch, which is mounted at the rear of the A/C compressor. The switch is wired internally to the compressor and is not serviceable. The switch opens and disengages the compressor clutch when temperatures reach 135°C (275°F). The switch closes when the compressor temperature cools to 120°C (248°F).
A/C compressor clutch will not engage under the following conditions:
- The A/C high side line pressure is over 2413 kPa (350 psi).
- The A/C low side line pressure is under 151 kPa (22 psi).
- Throttle angle is at 100 percent.
- Engine speed is more than 5500 RPM.
- Engine coolant temperature (ECT) is more than 123°C (253°F).
- Ambient air temperature is less than 1°C (35°F).
- Engine is idling at a low unstable RPM.

Compressor clutch engagement cannot be used to determine 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.