A/C Pressure Switches
WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
A/C high and low pressure switches may be used in the A/C compressor clutch or compressor clutch relay circuit. Switches are normally closed, completing the circuit which energizes the compressor clutch. When system refrigerant pressure increases beyond a certain point, high side switch opens, causing compressor clutch to disengage.
If system refrigerant level decreases (causing refrigerant pressure to drop), low side pressure switch opens, preventing compressor damage by causing compressor clutch to disengage.