Park Avenue Ultra V6-3.8L SC VIN 1 (1991)
A/C Signal: Description and Operation
A/C Head Pressure Switch
A/C Head Pressure Switch And Fan/Relay Circuit
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 ECM/PCM that the A/C system is operating. The switch grounds a terminal of the ECM/PCM when closed. When the switch is closed (A/C
operating), the ECM/PCM operates the engine cooling fan relays so the fans run at high speed.
