View Full Version : Function of the A/C pressure switch?

04-27-12, 12:53 PM
What exactly does it do? Should it turn of the compressor if the pressure is too high, or does it simply turn on the fans at a certain pressure?<br><br>My reason for asking:<br>Cruising around friday night, the DIC shows that the alternator is not charging. By the time i hit the buttons to check the voltage, it's charging normally and I haven't had and problems with it since. <br>Didn't think much of it, till......I notice a bunch of oil spots under the car sunday. Found the A/C belt was shredded and figured the compressor was shot and coughed up all its oil. Cleaned up under the car and not a drop of oil since (dip stick level is good and has not changed either). <br><br>I installed a new belt tuesday and everything seemed to run perfectly for the few minutes I ran the A/C. No noises, clutch working properly, cold air and no more oil leaks. So I check for codes and bring up 622 and 651. There was no CEL, so this happened only one time. Reset the codes and they haven't come back all week. One of the codes has to do with 5V that goes to the A/C pressure switch.<br><br>I've heard that some (all?) compressors have a pressure relief. Could it be that while the A/C was on friday, the switch wasn't getting power and couldn't turn on the fans resulting in the compressor dumping some oil/134A to keep from blowing to smitherinies?<br><br>I'm picking up a set of gauges and will check the pressure this weekend.<br><br>Thanks<br>Tony

04-27-12, 03:34 PM
A/C Refrigerant Pressure Sensor
The A/C refrigerant pressure sensor is a 3-wire piezoelectric pressure transducer. A 5-volt reference, low reference, and signal circuitsenable the sensor to operate. The A/C pressure signal can be between 0-5volts . When the A/C refrigerant (http://www.alldatadiy.com/alldatadiy/DIY~V31295839~C40138~R0~OD~N/0/108596970/110536423/110536424/110536428/34853741/34865608/56273766) pressure is low, the signal value is near 0 volts . When the A/C refrigerantpressure is high, the signal value is near 5 volts .

The A/C refrigerant pressure sensor prevents the A/C system from operating whenan excessively high or low pressure condition exists.

If the ECM detects a failure in the A/C refrigerant pressure sensor or circuit,the class 2 message sent to the HVAC control module will be invalid. The HVAC control module will then send a request to the Radio for display of the SERVICE A/C SYSTEM that will be displayed on the DIC. The HVAC control module will also display A/C OFF on the module as long as the condition is present.

04-27-12, 03:50 PM
Thanks D!!! I was hoping the answer was simpler. But I guess I'll start by checking the pressure and go from there.
I'll be sure to update when I figure it out.

BTW I have no idea why my 1st post looks like that. Sorry if it's hard to follow.