I was just wondering if someone could give me some input on what to expect or what to look for. Basicaly the compressor is good(clutch too) , there is free-on in the system, the air blows, the compressor turns on, but the air stays hot.....I have hooked guages to the system and noticed that every 30 seconds or so, the pressure cycles up to a dangerous psi, then I hear a click and it cycles back down......IS THERE A BLOCKAGE IN THE SYSTEM? Somebody......Anybody.......HELP! It is already almost 100 degrees here in South Florida, and as we get deeper into the summer, the humidity will be like being in the rainforest.....I go to work in a button down(long sleeve shirt) and slacks, I went in the other day SOAKED.....Anyways, you get it......

Are you sure one of the heat blend doors is not stuck in the heat position, or that an air recirc/outside door is stuck shut? It is entirely normal for an a/c unit to cycle, particularly in a car, and if a blend door is stuck the evaporator cools rapidly and trips the compressor on high discharge pressure. The cycle repeats as soon as the small volume of air in the evaporator box heats enough to trigger another cool cycle.

Touch the aluminum lines coming from the firewall at the heater coolant connector and at the right (passenger) side of the radiator. Is one cold?

What are your high and low side pressure ranges?

SUB:...You make a good point , I did notice that it did attempt to get cold when I put alittle bit of refridgerant in it ,as it was low....but it only got cool from the 2 right ducts, the 2 left ones were blowing hot air......but eventually, both sides reverted back to hot air, even after putting in refridgerant.

That is a classic example of low refrigerant in a dual zone system.

Ranger, if its just low refrigerant, Id be ecstatic.....on saturday a freind of mine who is a tech will put in his bay, we're going to vac it it out , then fill it up and go from there....

Low refrigerant means a leak in the system so make sure to add leak detecter dye as well. reinspect in a week to determine source of leak.

Anytime the system has been opened to ambient air the receiver/dryer should be replaced and the system vaccuumed out. Not sure if this is the case with yours. NAPA has them for ~$30. The system holds 2lbs of R134A. Thats almost 3 12oz cans(~using2.66cans) w/o replacing the receiver/drier. If you replace that you'll need 2 4oz PAG150 oil charge cans which contain 2ozs R134A and 2ozs oil...then 3 12oz cans of 12oz R134A(using~2.33cans). Verify operation with a set of low and high pressure guages, then give it a couple days of use before it actually reaches max efficiency.
Doug

Doug, I have a question for you as you seem to know a lot about the A/C system in a Seville. If I need to replace my compressor (it's over 7 years old), I have found several A/C shops that will "flush" the system for about $70. The condition being that the drier is removed, the orifice is removed and the manifold to the compressor (which connects to the condenser coil) is accessible. OK, let's say I can provide all of that, but upon replacing the compressor, how much and WHERE do I add the 8 oz of PAG 150 oil? Does 4 oz go in the compressor and 4 oz in the evaporator coil or some other splits? I haven't been able to get answers on this. Thanks! Greg

Well, first let me say if the compressor isn't broke, it probably isn't. Without the proper guages its near impossible to determine if a system is working at max efficiency and a system flush is only if the compressor got trashed. Even then, the high side line from the compressor to the condensor, then to the orifice is as far the crap goes(most of the time). I beleive its a Mitsubitshi compressor...better then most of the other GM ones. The R4(harrison) was a real turd and a few others eat clutch bearings by 75k miles. Anyway, when replacing the compressor, the required amount of oil as stated in the factory service manual is placed within it. Make sure you hand turn it while adding the oil to prevent hydra/oil lockup of it. Most compressors ship with oil in them, so the oil has to be drained and replaced. Any other replaced component I fill the low-side port with the oil charge. The 98-04 caddy system uses 150 weight PAG oil, unlike most of the other GM vehicles. I find it in both pressured and unpressured cans at either a NAPA or Carquest parts stores.
Doug

Thanks Doug...you're right...if it ain't broke, don't fix it! But I have a "gut" feeling mine could go anytime and then I will embrace the project. I think my 97 SLS has the "H6" compressor, or at least someone posting here believed that to be true. It was replaced in 2001 so the original conked out after 5 years of service. Right now, I can hear a "growling" noise which I suspect is the clutch bearing, but it might be better to wait for the whole unit to fail and replace it in one operation.
Getting back to PAG oil...so the oil shipped in a replacement compressor is not correct? You suggest draining it and replacing it with PAG 150 while hand cranking. Would I measure how much oil was shipped in it and then re-add that same quantity? I've read many threads on the subject and the consensus is that the TOTAL capacity of the system is 8 oz. So some goes in the compressor and some into the coils? Thanks again...Greg

If the clutch bearing goes, either 1 of 2 things happen, the compressor is on all of the time or the belt smokes. Neither are good. A clutch bearing replacement on-the-car can run $200-250. A good choice if the system has never been opened or doesn't exhibit any other issues and you trust your mechanic has the exact tools.
If you get a gm/factory replacement compressor, yea it has all the oil you need ~3ozs. Bolt it up and run with it. If you purchase it somewhere else, there ain't no tellin whats in it or how much.
Here's the component replacement oil capacities:
compressor:3ozs
receiver/drier:4ozs
evaporator:1oz
condenser:1oz
Notice they dont add up to 8oz...most a/c failures are leaks which generally speaking lose oil during the leaking of freon. The extra oz is for insurance when repairing.
The oil in the system will redistribute itself in the system during use. Thats why it takes a couple of days of running it to let it 'equalize' and reach max efficiency after a complete recharge.
Doug

Doug - thank you so much for your answers! I now have the information I've been seeking for a long time. I will assume that when the components of the system are flushed properly, ALL the old PAG oil in them is purged out during the process. So before replacing components and re-tightening all the connections for vac/recharge, the quantities of PAG 150 oil you recommend should be added to each. I will verify that with the mechanic who quoted me on the flush. Also, thanks for the tip on "redistribution" of the oils...I did not know it took a few days of operation for that to happen.

One more question...after a vacuum is drawn and holds solid for an hour, should the compressor be "running" during the addition of the 32 oz of new refrigerant or should it be done with the engine off?
Thanks again - Greg

Thanks for the input everyone....I will keep you all posted after saturday.....

For sure, let us know what happens....

I usually put the oil can in first w/o the motor or compressor running, then connect the 2nd can of oil or freon, and crank the motor and run the compressor, sometimes having to shake the can to keep the low-side from dipping too low on the guages and the system cutting the compressor off. Continue with can after can, trying not to get any excess ambient air in the lines/system during that process until the proper amount is added. Do not overfill, it'll kill the compressor.
Doug

And DO NOT use refrigerant with a "sealer" in it.

Ok gentlemen, a semi -verdict is in. I went to my buddys shop , we hooked it up to the vac machine, there was next to nothing in the system....vac held perfectly for the 20 minutes we left it on..hence no leak or at least not a fast one....we then filled it up with the machine to the full 2 pounds....the system started working perfectly, immediately got ice cold from all the ducts, actually for as long as Ive owned the car the 2 left ducts never were as cold as the 2 right ducts, now all ducts are very cold. Ran it hard all day, on and off....so far its working great. Car is over 7 years old now and has never had an ac service.....natural evaporation of refridgerant can be as much as several ounces a year......maybe the system was low for a couple of years now....hence the 2 left ducts not cooling as well as the 2 right.....and now has a full charge, I may be good for as long as I own the car.....keep youre fingers crossed....thanks guys.....as we Italians say AREVERDERCI!

....natural evaporation of refrigerant can be as much as several ounces a year...

To any and all techs: Is this true? If so, I should have the pressure checked on my system to see if there has been any refrigerant loss over the 7 years it's been in operation. The vents are cold and I don't get any messages so at what point (or pressure) do the sensors report "low refrigerant level"?

False!!! Refrigerant doesn't evaporate or wear out (in a closed system). If you have a leak it will boil to a gas and head to the clouds. Every time you put gages on a system you end up shorting the refrigerant charge about 2oz. If it's working well leave it alone. Clean the condenser if dirty and change your cabin air filter.

Refrigerant molecules are very, very small and can leak from the tiniest of places. That's why the service port caps are an integral part of sealing the system. It is not uncommon to have to add some refrigerant every 5 years or so. "Several ounces per year" would indicate a problem.

Thanks Ranger and mramazing...maybe the next time I have my SLS in, I will ask that it be checked just to be sure as the system hasn't been looked at in over 7 years. I agree, though, if it works...don't fix it!

GENTLEMEN!....Im back with .....bad news.......24 hours after my ice cold full charge....system is blowing hot air again....I dont know what to think....vac held up good for almost 20 minutes, how can it all leak out that fast? We did put dye in the system, but I never checked it, my buddy said at least if I take it in for service, they will be able to put on those "infrared goggles" and tell me where its leaking from.....I am so diddapointed and HOT!....literally....

msta, it sounds like you have more serious problems...do you get the "low refrigerant level" message on the DIC? Like Ranger says, the leak could be anywhere in your system including possibly the evap coil, which is the worst case scenario. BTW, from threads I've read here, holding a vacuum should be done for 1 hour to be sure before a recharge is done. Is your compressor original? It could be shot. Have someone look around the seal at the bearing/clutch for dye leakage.

You definitely have a leak somewhere. You didn't leave the vacuum pump running for the 20 min. while you watched for a leak did you?

YES Ranger....We did have the vac pump running and the numbers stayed the same for almost 20 minutes, my buddy said if I had a BAD leak we would see it change inside of 5 minutes.....So I ruled out a bad leak......but 24 hours later empty?....somethings leaking bad.....compressor is original and working VERY WELL( when there is refridgerant in the system)......well....."infrared goggles, here I come.....stay tuned.....

msta, I think the evacuator should be turned off during the vac/hold test. If you leave it running, your gauge could give a false positive on holding "zero". Yes - if you've already done the dye then start looking signs of leakage. There are areas to check that require getting under the front and below the compressor where the manifold connects. Good luck and hope that it's not your evap coil which is embedded in the firewall cowl. BTW, I've collected lots of notes on how to DYI, but if you have a good mechanic working on the system, hopefully you are OK.

Greg is right. Pull the vacuum and then close the valves and shut down the vacuum pump. NOW see if it holds a vacuum.

Will do guys......thanks again for all the input....I will post back for all with any interest.........

Will do guys......thanks again for all the input....I will post back for all with any interest.........

Eagerly following this thread as I'm also having this exact problem.

Took my car to two places and both claimed that the vacuum was holding. Car would blow cold air immediately after recharging but the next few days it'd be gone again.

I wonder where the urban legend started about freon evaporating came from? Drawing a vacuum is much like adding air to a tire. It wont show a minor leak as long as you add air, but remove the air hose (ie, turn off vacuum pump) and see if the leak appears. GM cars for years were designed to leak small amounts of freon and oil from the compressor front seal because of infrequent use is certain areas of the US. They thought waste a little bit of oil and freon to add years to the compressor I guess.