A/C Request Signal

2004 Oldsmobile Bravada AWDSECTION A/C Request Signal
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.

The A/C system can be engaged when the VENT switch is pressed or the HVAC control module is in FRONT DEFROST, MIX-BLEND mode or during automatic operation. The HVAC control module sends a Class 2 A/C request message to the Powertrain Control Module (PCM). The following conditions must be met in order for the PCM to turn on the compressor clutch:

  • HVAC Control Module  - Ambient temperature is more than 40°F (4°C).
  • PCM  - Engine Coolant Temperature (ECT) is less than 255°F (124°C), Engine speed is less than 5000 RPM and A/C Pressure is 410-30 psi (2826-207 kPa).

Once engaged, the compressor clutch will be disengaged for the following conditions:

  • Throttle position is 100 percent.
  • A/C Pressure is more than 410 psi (2826 kPa).
  • A/C Pressure is less than 30 psi (207 kPa).
  • ECT is more than 255°F (124°C).
  • Engine speed is more than 5000 RPM.
  • Transmission shift.
  • PCM detects excessive torque load.
  • PCM detects insufficient idle quality.
  • PCM detects a hard launch condition.

When the compressor clutch disengages, the compressor clutch diode protects the electrical system from a voltage spike.

RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • You smell fuel, burning insulation, or see smoke.
  • Brakes feel soft, pull hard to one side, or make grinding noises.
  • The engine overheats, stalls repeatedly, or misfires under load.
  • You are missing required tools, torque specs, or safe lifting equipment.
  • You are not confident in the next step or safety outcome.