A/C Mode: Notes

WARNING: This page is about a different car, the 2002 Pontiac Firebird and 2002 Chevrolet Camaro. However, it is still accessible from the selected car via links, so may be relevant.

The purpose of the air conditioning (A/C) system is to provide cool air and remove humidity from the interior of the vehicle. The vehicle operator can activate the A/C system by activating the following modes:

MAX A/C
A/C
BI-LEVEL
MIX-BLEND
FRONT DEFROST

The A/C system can operate regardless of the temperature setting, as long as the ambient air temperature is above 38°F (3°C). If the A/C compressor clutch is turned off due to cold ambient air temperatures, the compressor will not come back on until ambient air temperatures reach 41°F (5°C).

Regardless of the selected A/C mode setting, a request is made to the Powertrain Control Module (PCM) to turn on the A/C compressor clutch. The request is made through the A/C request signal circuit from the HVAC control assembly. Power and ground are provided to the HVAC control assembly by the ignition 3 voltage and ground circuits.

When the vehicle operator makes an A/C request, a 12 volt request signal is sent out over the A/C request signal circuit and grounded through the PCM. When this request signal is grounded, the PCM can activate the A/C compressor clutch.

The PCM turns on the A/C compressor clutch by providing a path to ground through the A/C compressor clutch relay control circuit for the A/C compressor clutch relay. Power is provided to the A/C compressor clutch relay from of the underhood fuse block on the ignition 1 voltage circuit. Once the relay closes its internal switch, power from the battery is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit.

Whenever the compressor is turned off, the A/C compressor clutch diode prevents a voltage spike from entering the vehicles electrical system. The ground circuit provides a path to ground for the compressor. The A/C compressor clutch relay control circuit is grounded internally within the PCM. On vehicles with the V8 option, an A/C compressor clutch status signal is sent to the PCM on the A/C compressor clutch supply voltage circuit.

The PCM will engage the A/C compressor clutch any time the engine speed is below 5000 RPM and the A/C is requested unless any of the wing conditions exist:

Throttle angle is at 100 percent (WOT).
Vehicle launch, hard acceleration from a stop.
Idle quality.
The A/C refrigerant pressure sensor is above 414 psi (2854 kPa) or is less than 35 psi (241 kPa).
Engine speed is more than 5500 RPM.
Engine coolant temperature (ECT) is more than 250°F (121°C) for the 3.8L and 257°F (125°C) for the 5.7L.
Transmission shift.
Engine torque load.
Top of travel clutch switch position, if equipped.