AC Compresser issue
Asked by Iedwards23 Aug 06, 2018 at 03:34 AM about the 1996 Mercury Grand Marquis 4 Dr LS Sedan
Question type: Maintenance & Repair
When turn the AC on in my car the compressor
doesn't come on. To test the compresser I jumped
pin 30 and 87 where the relay goes. The
compressor comes on with that test. That led me
to think that maybe compressor is not getting
signal from computer. I started the car and turned
on the AC and checked the voltage on pin 86 and it
has 11.3V. I have tested the relay and it is working
properly. I also tried another known good relay just
to make sure, but still not working. Pin 85 is
supposed to be the ground and appears to good.
Need help figuring out what is the problem.
4 Answers
Iedwards23 answered 5 years ago
Its a 5 pin relay. When I connect 30 to 87 the compressor kicks on. Are you saying that 30 to 87a should keep the compressor on and 30 to 87 should turn the compressor off.
Iedwards23 answered 5 years ago
Thats exactly what I thought about trying, using an external ground. I will do it tomorrow and let you know what happens
Iedwards23 answered 5 years ago
I did some testing and the results are pretty strange. With car on and AC on I only get voltage on one side of the low pressure switch (2 pin). This is strange because I replaced the low pressure switch when I replaced the accumulator/ drier. I tried to complete the circuit with a paper clip inside the connector but still not getting voltage on the other pin. Then I basically bypassed the connector by linking the two back probes with test leads, but still don't get compressor to turn on. I thought I had two issue because even after link the connections by connecting test lead to back probe, I am still not getting voltage inside the connector on one side. So assumed I have a bad connector. Then to my surprise I don't see voltage on either pin on the high pressure switch. I apply power to one pin but I don't get voltage on the other one. When trying to complete the circuit on the high pressure connector with paper clip, I still don't get power on the other pin. I highly doubt that I have 2 bad connectors. I basically bypass all the connectors going to the PCM but still can't get compressor to turn on. I was also able to get the compressor to kick on if I use the battery ground for the relay instead of the PCM. Anybody have any ideas. I'm ready to just get a junkyard PCM and if that doesn't work I'll just rig up a switch.LOL. But it is really bothering me not knowing what is causing this problem.
