A/C Pressure Sensor & Switch

WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

The PCM monitors the A/C refrigerant pressure switch signal circuit. If the PCM detects a pressure signal out of parameters, it will disable the A/C request. This switch assists in cycling the A/C compressor and prevents A/C compressor operation if system has a low refrigerant level. The sensor information is used by the PCM to determine A/C system load on the engine and A/C system pressures. Once engaged, the compressor clutch will be disengaged for the following conditions:

Ambient air temperature is less than 40°F (4°C).
Throttle position is 100 percent.
A/C high side pressure is more than 455 psi (3140 kPa).
A/C low side pressure is less than 28 psi (196 kPa).
Engine coolant temperature is more than 250°F (121°C).
Engine speed is more than 5500 RPM.
PCM detects insufficient idle quality.

The A/C refrigerant pressure switch prevents the A/C system from operating when an excessively high or excessively low pressure condition exists. The PCM enables the compressor clutch when A/C pressure is between 28-455 psi (196-3140 kPa). A/C refrigerant pressure switch can also ground the control circuit of the fan 2 relay, thereby switching the cooling fan from low speed to high speed. The switch is open below 178 psi (1226 kPa) and closed above 220 psi (1520 kPa). The change in fan speed improves the condenser's ability to lower refrigerant temperatures and pressures.

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

Ambient air temperature is less than 40°F (4°C).
Throttle position is 100 percent.
A/C high side pressure is more than 455 psi (3140 kPa).
A/C low side pressure is less than 28 psi (196 kPa).
Engine coolant temperature is more than 250°F (121°C).
Engine speed is more than 5500 RPM.
PCM detects insufficient idle quality.