A/C Refrigerant Pressure Switch
WARNING: This page is about a different car, the 2004 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.
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 the A/C pressure is between 196-3140 kPa (28-455 psi).
The 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 1226 kPa (178 psi) and closed above 1520 kPa (220 psi). The change in fan speed improves the condenser's ability to lower refrigerant temperatures and pressures.