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Strange GM Problem

Mmfh on Thu July 16, 2009 11:02 PM User is offline

Year: 94
Make: Buick
Model: Regal
Engine Size: 3.8
Refrigerant Type: 134
Ambient Temp: 85
Pressure Low: 30
Pressure High: 175
Country of Origin: United States

Hello everyone,
I spent a few hours on this today and I don't know whats going on with it.

This thing came to me with nothing happening, no compressor action. I checked pressures and found that the static pressures were about 10 on the low side and about 50 on the high. With everything set to call for AC I had no power to the clutch but I did have power to the relay and the relay was good. I unplugged the low pressure switch and shorted it with a paper clip and nothing happened. I found the high pressure switch and was going to do the same thing but as soon as I unplugged the switch the electric fans started running but still no power to the clutch.

After replacing the relay because I had power to the relay and no power to the clutch I found the same thing with the new relay. No power to the clutch. I found that by-passing the relay in the box I could get power to the clutch and the system would blow cold air after I added a can of freon. Now my running pressures are about 30 low and 175 high while its close to 90 outside. It actually cools pretty good and I'm sure my customer would be pleased if I could figure out this electrical problem.

At this point I have the relay by-passed with a paper clip and the high pressure switch is unplugged. If you try to plug in the high switch the fans and the clutch stop like I just shorted everything out. Not like I flipped a switch but like it was shorted as the fans bogged down and went very slow as if shorted before I unplugged the high switch again. Once I unplug the high switch again the fans speed back up and the compressor spins like normal again.

Now remember this whole time I have the relay by-passed with a paper clip because if I install the new relay nothing happens. Also I checked the high switch and it is closed!

So, while the high switch is plugged in the system is dead and no power to the clutch. Also no power to the clutch unless the high switch is unplugged and also the relay is bypassed with a paper clip.

I really need to get this done as a couple of old ladies with no money need to go to the doctor and they can't take the heat!!

Thanks very much for your info, Have a great day!!

JJM on Fri July 17, 2009 12:10 AM User is offline

Is the check engine light on? Any codes stored? If so, did you clear (disconnect the battery for a minute) after the repair?


When considering your next auto A/C purchase, please consider the site that supports you:

Mmfh on Fri July 17, 2009 12:33 AM User is offline

No there are no codes and no light.
I didn't think on a '94 there were any codes for the A/C system??

Anyway, nothing going on in that way.


Chick on Fri July 17, 2009 7:54 AM User is offlineView users profile

At 85 degrees a 10psi or even the high side of 50, shows your system is just about empty.. Your problem is most likely the pressure transducer, the three wire switch on the high side side line. It tells the computer to send the ground to the relay, and the fans.. Try that, then do a proper evacuation and recharge, and might want to find and fix the leak, most likely the shaft seal and body leaks on the compressor..Hope this helps......

Also check the harness to the transducer, they sometimes become loose and make a bad connection..

Email: Chick


Freedoms just another word for nothing left to lose

mk378 on Fri July 17, 2009 10:21 AM User is offline

The pressures when it came in show that it was basically empty. It'll take more than one can to get back to full charge. Spend some effort looking for the leak, there is going to be a leak.

Probably the ECM has gone into compressor lock out after it detected the undercharge. This might set a code that can be read with a scanner, but it will not turn the check engine light on. Also some models had the lock out feature implemented in the HVAC control panel instead of the ECM. Try plugging everything back in stock, and reset the computer(s) by disconnecting the battery.

Mmfh on Fri July 17, 2009 10:30 AM User is offline

I will check as stated above and also unhook the battery to see if that will clear anything.

I'm confused though, I didn't think on an old '94 Buick that the manual A/C system had any kind of computer control??

Oh in regard to stated above, the transducer on this model is only a two wire. #25604949

Can anyone tell me on the high and low switches. Are they normally open or closed??

Thanks very much, any other idea's I would love to hear them too.



Edited: Fri July 17, 2009 at 10:36 AM by Mmfh

Chick on Fri July 17, 2009 12:55 PM User is offlineView users profile

Yes, you're right, that car didn't use the V5 in the 3.8 engine, so you have a cycling compressor with a two wire cycling switch..Sorry, wasn't fully awake yet, do as mk378 suggested in resetting the computer by battery disconnect.. and then you should be able to recharge from vacuum by jumping the cycling switch

Email: Chick


Freedoms just another word for nothing left to lose

GM Tech on Fri July 17, 2009 5:34 PM User is offline

You have a low charge code set in the control head- (not the Ecm) ..the a/c relay needs the negative lead of the coil energized by the ecm- to switch on the compressor- the ecm is saying no way- because of the low charge- resetting the battery will clear the code 46. Your system has no transducer- it has a HPCO switch on the rear of compressor- or on pipe next to it--wired in series with the cycling switch-- the cycling switch is normally open- closes with 47+ psi pressure- the HPCO switch is normally closed- opens with 427 psi or more pressure...

Lots of difference between the 3.8L H-6 and the 3.1L V-5 systems.......

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......

Mmfh on Sat July 18, 2009 10:37 AM User is offline

You guy have been very helpful!

Its doing great now and as most of you said just clearing the computer and charging the system up did the trick!!

Because of health problems I've been away from cars for about 15 years and now because of money problems I'm back at it. Things have changed for sure.

Thanks very much, Have a great day!

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