A/C Head Pressure Switch

Circuit Diagram (A/C - Engine Cooling Fan Relays):

The A/C head pressure switch is a normally open switch that closes when the compressor head pressure is greater than approx. 200 psi (1380 kPa) to signal the PCM that the A/C system is operating. The switch grounds a terminal of the PCM when closed. When the switch is closed (A/C operating), the PCM operates the engine cooling fan relays so the fans run at high speed.