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Old 09-20-2010, 10:58 AM   #1
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2002 Pontiac Firebird
 
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Default AC Not Cooling & Low Pressure reading seems high?

Wondering if anyone has seen this behavior and can point me in the right direction?

A little history -
I have a 2002 WS6 R/A TransAm. 2 months ago I drove it cross country. While running across the desert, I noticed that it tended to freeze up and quit pushing cold air every couple hours. So I'd stop at a gas station, turn it off for about 10 minutes - and then when I started it back up I'd have nice icy cold air again. Assumed this was a combo of probably low freon and super hot desert temps. BTW - I've never had the freon recharged. So I figured it was about due for some freon. Seemed to work fine for the rest of the trip. (desert was the first day)

So fast forward 2 months and I'm noticing that it's cooling off for me less and less. Now almost not at all. It's over 90 degrees here so the problem now has my full attention. The AC seems to blow air strong enough - it's just not cold. It's not as hot as the air outside - but you'll start sweating if it's midday.

So we hooked up the pressure gauges and read about 72/74 on the low pressure side and 200 on the high pressure side. Thought that was odd - Theorized that if the high pressure side should be up to about 300 that it must have a leak and need freon. Added a can of red devil and some freon. We got the high pressure side up to about 250 - but the low pressure side didn't do much of anything in the way of a drop. Just a slight drop - Might have kissed 68/70 on the gauge? When we let the two sides equalize, they're both pretty close to the 125 or so mark. So I think that means the gauge is working the way it should. We thought the low pressure side should sit around 35 - and since I'd never recharged the system, didn't understand the higher reading.

The dryer (I think it's the dryer - silver can?) used to get "frosty beer can cold" but in the last few weeks (since I noticed) it's only mildly cold. It does sound like the compressor is cycling on while the air conditioning is running. At least I think that's what I'm hearing.

Also - I ran my CarMD today and it doesn't seem to be throwing any new codes. I do have a code for the catalytic converter (P0420) - but that's not new. I have not pulled the fuses to reset the brain - but could give that a try and see if it helps.

Has anyone ever seen this behavior? I'm not sure where to start looking on this one.
Many many thanks in advance for any suggestions!
More than happy to take pics or video of anything helpful!!
It's sooo hot - so really hoping to get my car air conditioner running icy cold again soon.
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Old 09-20-2010, 02:03 PM   #2
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BTW - I found this article on diagnosing A/C problems. It indicates that on a 90 degree day, the correct reading for the low side SHOULD be around 70 or higher. Has a neat chart to compare your low and high pressure readings against and indicate the problem spot.

Does anyone agree or disagree with this?
http://www.aa1car.com/library/ac98.htm

THANKS AGAIN!!!
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Old 09-20-2010, 02:25 PM   #3
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The pressures are going to be different depending on ambient temp and humidity. Try searching the site and see if there's an A/C Perfornance Chart for your year or maybe someone can post one. Here's what my Helms says for one set:

86-95*F - Below30% humidity 40-44 psi low/213-251 high, 66*vent.
Above 30% humidity 42-46 low/218-261 high, 68* vent.

Edit: Your P0420 is for a bad drivers side cat - you might still be under the GM 10 year/120K extended warranty for it.
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Old 09-20-2010, 05:26 PM   #4
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I have done some residential air conditioning this summer. A system that is overcharged with refridgerant will not give you proper cooling. I'm not sure what pressures R-134a runs at but if it is as low as 2001nbmz28 says its supposed to be, then I would release some gas out of the system. If you have a thermometer, you can measure the air blowing out of your vents. Then let few psi go at a time, and wait about 3-4 min then recheck your thermometer to see if the temp drops. If temp drops, keep releasing gas until temp bottoms out or stop when your happy with the temp. If you may have to add a few psi if you release too much. Close to 50 degrees came out of the my work truck vents when I measured it one day. This is how I was taught when we were doing residential (using a recovery machine of course). A 10 or more degree celcius difference between return and supply air ducting of a home shows a properly working system. Condensation also another indication of a properly working system.

Worth doing if everything else is working properly.
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Old 09-21-2010, 02:33 PM   #5
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Quote:
Originally Posted by 2001NBMZ28 View Post
The pressures are going to be different depending on ambient temp and humidity. Try searching the site and see if there's an A/C Perfornance Chart for your year or maybe someone can post one. Here's what my Helms says for one set:

86-95*F - Below30% humidity 40-44 psi low/213-251 high, 66*vent.
Above 30% humidity 42-46 low/218-261 high, 68* vent.

Edit: Your P0420 is for a bad drivers side cat - you might still be under the GM 10 year/120K extended warranty for it.

Thank you both!

1st - Wow! Thanks for the tip on the cat!! I'd priced them before (yikes!) and decided it could just keep throwing that code. I called this morning to find out. The first place I called wanted my vin number and sort of hemmed and hawed around. The second dealership I called just got back to me - asked my mileage and said yes, I was covered since I'm only up to 111k. So I've got an appointment a week from today for them to scan the code on their end and then order the part. Yippee!! Thanks so much!

Now back to the AC issue. I flipped the house over last nite looking for a thermometer for an accurate reading. Saw that Harbor Freight has their $60 Infrared Thermometer on sale (Today only and must print coupon?) for $25.99.

So I now own one and can say with some certainty that my car isn't cooling at all. The temp reading varied right around 90-93 degrees. Same temp as outside. I'm down near Tampa, FL and the temp outside is sitting at 90. Humidity is 43% according to the local weather channel.

I guess I just thought it was cooler because the car interior is about 20 degrees hotter sitting out in the sun. (registered 111-113 shooting the ceiling or down at the gas pedal - items in "shade") Doh.

That Helms chart - is that referencing a 2001 Z28? (based on your user name) It looks like the GM service manuals cover Firebird and Camero in the same book. Tho dunno if the ratings are the same though my guess would be yes.

My initial reading was about 70 low side / 200 high side. (pre-freon add) Should I still try and bleed off some of the freon that we added to push the high side up to 250?

Do you guys think that the compressor could be bad even though it's running? The diagnostic chart that I found suggested if the LP side registered High, and the HP side registered low - that the compressor or the control valve has failed. I've got the exploded diagram of the system but still studying it to try and figure out which "control valve" they're talking about... And I assume I'd have to open the system to change it once it's identified? Anyone know which valve they're talking about and how to test for failure? (apart from hotternell AC air?)

I believe there's an AC parts wholesaler up in Jax with some good deals - and my dad is up there for a couple days. Hoping I can figure out what I need and ask him to pick it up for me before he comes back. (unless I look at the ebay route for a deal)

Ugh - That learning curve seems extra steep when it's tied to your AC - LOL! Thanks again for all the help!!
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Old 09-21-2010, 03:19 PM   #6
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Yeah the Helms is the GM service manual for my 2K1, yours should be the same. I've done home AC R22 systems but don't know that much about car systems. Good deal on the free cat replacement though - maybe ask them to put gauges on the AC while the car is in for the cat replacement?
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Old 09-21-2010, 05:21 PM   #7
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Quote:
Originally Posted by 2001NBMZ28 View Post
Yeah the Helms is the GM service manual for my 2K1, yours should be the same. I've done home AC R22 systems but don't know that much about car systems. Good deal on the free cat replacement though - maybe ask them to put gauges on the AC while the car is in for the cat replacement?
Well I just ran it through an AC shop and they were SUPER Super nice. They pulled all the freon out of my system and took it down to empty and then put it back in up to the factory measurement. They said it would correct if we'd overcharged it - and could also help to pull any moisture out if that was the problem. The low side pressure stayed high when they put it back - which they said indicated the compressor was done.

Are your helms books the same GM Service Manuals? Green 3 or 4 volume set? Are they the most comprehensive books floating around? I'm going to see about getting some so I can see what's involved in the switch.
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Old 09-21-2010, 05:21 PM
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