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1998 Grand Prix GTP AC Help

rodneypierce on Tue July 02, 2013 10:24 AM User is offlineView users profile

Year: 1998
Make: Pontiac
Model: Grand Prix
Engine Size: 3.8
Refrigerant Type: R134
Ambient Temp: 85
Pressure Low: 60
Pressure High: 100

Hey guys, I have a 1998 Pontiac Grand Prix. The A/C isnt blowing cold at all, in fact its blowing hot air (around 93* air). I hooked up my manifold gauges, and got a high pressure reading on the low side, and a low pressure reading on the high side. The compressor engages and continues to run. It doesnt make any noises. Runs smooth. The fan is kicking on and staying on shortly after the compressor kicks in. Everything appears to be working properly, except I cant get the high side pressure to raise, and the low side pressure to drop. Im pretty new to a/c, but have recharged a few cars before with no issues. This one has me scratching my head though?

Thanks in advance for any help!!

Rodney Pierce
Cedar Rapids, IA

GM Tech on Tue July 02, 2013 11:46 AM User is offline

65% of all mobile a/c failures are due to loss of refrigerant due to a leak-

2% of V-5 compressor failures (yours is a V-5) are due to a bad control valve--

So I check that the proper amount of refrigerant is in the system first- then I look for a pumping issue- as in your case a suspect control valve- just based on the numbers above..

Control valves are replaceable after you discharge the system- it is in the rear of the compressor- sometimes you are able to remove it without removing compressor from engine.

Other than that- are you certain gage set valves were closed when you measured pressures?

-------------------------
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......

rodneypierce on Tue July 02, 2013 1:25 PM User is offlineView users profile

Hey GM. Yes, Im sure they were closed. Ive been messing with it for a couple days. Have double traced everything to make sure I wasnt missing something or over looking something. Ill have the system evacuated and vacuumed down. Then I will refill it with 2 lbs of refrigerant. See if we get any difference. If not, I will try and replace the control valve.

The car was vac'd down and recharged before I bought it, and the A/C worked fine when I got the car about a year and a half ago. I hadnt tried to use the a/c until here recently and noticed it was no longer blowing cold. The pressures in the system lead me to believe that there was in fact refrigerant left.

GM Tech on Tue July 02, 2013 1:28 PM User is offline

V-5's will run with as little as 5% system charge in them - that's about 4 ounces - a whole lot less than the 2 lb bogie..

-------------------------
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......

rodneypierce on Tue July 02, 2013 1:32 PM User is offlineView users profile

10-4. Ill report back here with any findings. Thanks again!

rodneypierce on Tue July 02, 2013 4:34 PM User is offlineView users profile

Hey GM where can I purchase the control valves at? Just for future reference?

rodneypierce on Tue July 02, 2013 4:43 PM User is offlineView users profile

nevermind. Found it. I believe mine has the "orange" valve?

http://www.ackits.com/merchant.mvc?Screen=CTGY&Store_Code=01&Category_Code=CompressorControlValves

rodneypierce on Wed July 03, 2013 4:20 PM User is offlineView users profile

OK GM Tech. I followed your advise and had it evacuated today. They said there was 20oz that they pulled out. vac'd down for 30 minutes, and it held vacuum for 15, so put back in 2 lbs of refrigerant. Now, the high side pressure will rise up to about 150 lbs, then kick the fan on and drop to about 125 or so. The low side will now rise to about 95 lbs when the high side is at 150, and then drops down to about 75 pounds when the high side drops to 125. All while its blowing 98* air out of the vents.

So, probably the control valve next?

Edited: Wed July 03, 2013 at 4:21 PM by rodneypierce

rodneypierce on Wed July 03, 2013 8:01 PM User is offlineView users profile

Alright! went and got a new control valve, put it in, vac'd the system back down again, recharged and now we have correct pressures and cold air!!! Now at about 200 or so on the high side and 35 on the low side. I need to go get one more can of refrigerant in order to get 2 pounds in her. But have 52* air coming our of the vents, which is much better then 98+!!

Thanks Gm Tech!!!

Edited: Thu July 04, 2013 at 1:15 PM by rodneypierce

GM Tech on Thu July 04, 2013 8:25 AM User is offline

cheaper than a new pump- right?

-------------------------
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......

rodneypierce on Thu July 04, 2013 1:16 PM User is offlineView users profile

heck yes!!! I did have to go buy the vac pump. But thats OK! As now I have all of the tools needed to recharge. Just dont have the machine to evacuate it. Which, I dont see myself getting any time soon! The best part is, even with the 2 lbs of wasted refrigerant in trouble shooting and having to buy the correct tools to do the job (gauge set and vac pump), it was STILL cheaper by a long shot then taking it somewhere, as they would have replaced the entire compressor Im sure.

Thanks again brother!!

Teana on Tue November 26, 2013 7:13 PM User is offline

I have a 1998 Pontiac Grand Prix GT. 3.8 engine.

I had problems with my air conditioner this summer. It would blow hot air out the drivers side and cool (not cold) air out the passenger side. Had Freon added and once it helped but the later part of summer it did not and I about died!
Now this winter I am having problems with the air blowing out the vents when the heater is engaged. I blows, but there isn't much air coming out the vents.


-------------------------
Teana

Dougflas on Tue November 26, 2013 8:24 PM User is offline

Teana, you probably have a freon leak. Look at the shaft seal fir oil residue.

GM Tech on Wed November 27, 2013 9:30 AM User is offline

You have a vacuum leak that drives the mode door--look down by battery for black plastic (little) line that will be cracked or broken in two- splice a rubber hose over both ends to connect it back-- this is your vacuum source line as it goes to the vascumm reservoir under battery and also inside to the mode door- when it gets absolutely bad- you can only get defrost out the HVAC box-- yours is halfway there now.

-------------------------
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......

Dougflas on Wed November 27, 2013 1:15 PM User is offline

Quote
Originally posted by: Dougflas
Teana, you probably have a freon leak. Look at the shaft seal fir oil residue. I ' m sorry I misread his problem. I was under the assumption that the AC died in the summer meaning it had lost it's charge.

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