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ac compressor won't engage

fcunha on Tue June 24, 2008 11:41 AM User is offline

Year: 1998
Make: Plymouth
Model: Grang Voyager

I have a thread going on for this problem and was recommended to come here.

I have read through posts for problems similar to mine.

Symptom #1 - Compressor Clutch won't engage
This occured all of a sudden. Was driving, ac was fine (was about 100 out that day), stopped at a store for about 1 hour, then no ac

1) AC compressor Relay and Fuse are OK
2) AC pressure sensor is sending .925 volts from pin 3 which is within 'normal' range
3) 0 volts to compressor clutch
4) When I jump the ac relay pins 87-30, the compressor engages immediately (even when the car is turned off)
5) When I do #4 with the car running get very cold air, but fails ac test on climate control panel

Symptom #2 - Vent controls (Def/Floor/Panel/Etc) not working
This was actually my 1st problem I was working to solve, but then my ac all of sudden went out (for reason noted above on Symptom #1) about a week or so later

1) Fails recalibration test (multiple exhaustive attempts)
2) Light sequence indicate that the driver side vent door problem (1 blink, 4 blinks - don't have papers with me)
3) Blower, ac, wipers, etc all work (well, except now ac doesn't)
4) Indicator light switches seem to work when pressed
5) Disassembled the Climate Control panel to see if I could find anything and found a quarter between the pcb and back metal cover

So at this point I have ordered a replacement climate control panel and man - the 1998 Plymouth Grand Voyagers with dual controls and rear window defrost are rare items.

Any ideas, suggestions, etc are greatly appreciated!

Thank you!!!

webbch on Tue June 24, 2008 11:46 PM User is offlineView users profile

There may be a better way of diagnosing this, but I'd be curious what the low and high side pressures are at a given ambient temperature, just for reference. That may determine if it's a pressure switch issue or something else.


fcunha on Wed June 25, 2008 11:18 AM User is offline

Hi Chad -

The a/c pressure sensor signal pin is returning the correct voltage that the PCM is looking for to activate the compressor clutch. Per, an a/c pressure signal of .1?? - 4.5 volts is 'normal operating range'. I got .9?? volts (don't have all my papers with me).

I can't test the high side as I don't have the equipment to do that. When I tried to 'charge' the low side with a gauge / filler I got at walmart, it was in the red - however I got word on another forum that the pressure will drop to normal when the compressor is running.

So bottom line is, why is the PCM not grounding the compressor relay to send volts to compressor clutch if it is getting an appropriate signal from the ac pressure switch?

I suppose I can jump the compressor relay again and check the charge on the low side with it running - but that doesn't seem to be the problem per above - unless of course is incorrect.


mk378 on Wed June 25, 2008 11:42 AM User is offline

Wait until you get that new control panel in. That is quite likely to fix it.

fcunha on Wed June 25, 2008 9:41 PM User is offline

Thanks! Will do. Coming Friday - Will post results.

fcunha on Fri June 27, 2008 7:58 PM User is offline

OK - Got the new control panel and my vent controls work and it passed calibration now.

AC compressor still didn't kick in so I bypassed the relay thinking maybe that I am low on refridgerant. Well, the loud squeeling noise came shortly after that and I can see the high pressure vent is venting.

I don't want to screw anything else up - so what would cause this?


GM Tech on Fri June 27, 2008 10:02 PM User is offline

By jumping the relay- you are making the decisions- not the car--- and now you forgot to turn on the cooling fans-- the car would do that to if it knew the a/c was requested and "on" the cooling fans have to be on or you will experience high pressure cut-outs-- but since you have the relay jumpered- it can't turn off the relay so the high side went so high 500+ psi that it is blowing off the safety valve to keep from blowing off a hose-- you are lucky you did not blow a hose near your face!! But you will never know this if you aren't using a high side gage set-- those death kits are not only death to the system - but possibly your death-- low side is not enough to look at- yo had better stop until you understand why the transducer is not signalling the PCM what to do-- the fans react to system pressure provided by the high side pressure abd evidently they too are not being told to come on-- the only thing in common to the inop compressor and the inop fans is the pressure transducer--if nothing else put a variable potentiometer across the proper leads to "fool" the PCM into getting the proper return voltage to 1) turn on the compressor and 2) to turn on the fans.

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

fcunha on Fri June 27, 2008 11:27 PM User is offline

OK - Gotcha...

Time to take it to a professional. It scared the crap out of me.

fcunha on Sat June 28, 2008 9:40 AM User is offline

OK - I am now a Darwin Award winner!

In my zeal to install and test my newly arrive climate control panel - I negelected to check if I reconnected the AC pressure sensor.

I plugged it in, ran cool down test, and BAM!!!! I was able to top off the system with a can of refr and the low side is icy cold!

Problem solved by replacing the climate control panel.

mk378 on Sun June 29, 2008 11:12 PM User is offline

Apply soapy water to check for leakage thru the relief valve. Sometimes they don't reseal completely. Other than that you should be good to go.

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