HELP!!! Weird A/C problem....

[nlp]

I have a 2002 D/A with 147,000mi and never had any A/C issue until the end of last summer.
On a 95+ degree day last year, I start my truck after it had been sitting for several hours, turn on the A/C and almost immediately I see a cloud of smoke (freon) coming from underneath the hood accompanied by a loud hiss. Immediately my A/C starts to blow hot air. I shut the A/C off and figured my clutch or compressor just burned up. It was Sept so I said screw it, I'll wait until next summer to fix it. During the winter I used by defroster and noticed the compressor kicking on and off making me realize that the compressor and/or clutch must be ok. So a few months ago and went and purchased a $29 can of R134A with the gauge attached to the can. I filled the A/C system until the gauge was in the green and immediately the A/C was blowing cold air like brand new. Awesome! Then today the same thing happened.
After the truck had been sitting, I start it up, turn on the A/C which was blowing cold air....then I see smoke (freon) coming from under the hood. Without hesitating I shut of the A/C.....waited a few minutes and turned it back on...it started blowing "cool" air but not as cold as normal.

What's going on??? Do I have a blockage somewhere? Is there some sort of pressure relief valve that is opening up and allowing the R134A to escape? Is my compressor and clutch going out? How do I fix this?
Should I take it to a chevy dealer or just a reputable auto A/C place?
Thanks!!!!!!!!

[Mark Rinker]

There is a hi pressure relief valve on the backside of the compressor.

Last summer, I was loading up the Kodiak on a very hot summer day, let it run for the A/C to get a headstart...when it let go, I thought the engine had overheated!!!

If you have the system professionally evacuated and recharged, it will probably clear up, but don't idle on hot days, the condensor needs buku air flow, and it will happen again, wasting your $$$ for the evac/recharge.

(Don't ask me how I know this...) :o:o:o

[Duramaster]

Does the fan clutch work? Is the condensor/ radiator plugged full of debris? A side note.................. have you replaced your cabin air filters lately? They will not affect what happened under the hood, but they do affect air flow out of the ducts in the cab. I do believe they were discontinued for the 2003 model year to current.

[rustyk]

The high pressure relief valve is a last-resort device. The high pressure switch should disengage the clutch before the pressure gets high enough to trigger the relief. There's a tendency for systems to be overcharged ( (left over from R-12 days).

Low range R-134a Hi-lo is 190/25, max would be 250/30. I had a friend who had recharged his system in PA, and when I checked it in FL because it wasn't working well, pressures were 350/45! The high pressure switch obviously didn't function. I took it down to 230/30.

[dually2002]

Does the fan clutch work? Is the condensor/ radiator plugged full of debris? A side note.................. have you replaced your cabin air filters lately? They will not affect what happened under the hood, but they do affect air flow out of the ducts in the cab. I do believe they were discontinued for the 2003 model year to current.

On the models that do have the the cabin air filters can they be removed with out any ill effect? They restrict air flow even when new,get dirty quick,expensive for what they are and I feel like they are not letting my system operate at full efficiency.

[DmaxMaverick]

If you don't want a cabin air filter, just remove them. Later models have the exact same system, minus the filters.

[nlp]

FYI, I took it to an A/C place right before closing time. They said it sounded like a classic case of a faulty fan clutch causing the system to overheat and over pressurize.

They said replace the fan clutch, evacuate and refill the R134a and it should be good as new.

Dealer wants $259.74 just for the clutch!!!!

Cabin filter is new, I replace them twice per year.

Thanks for all your responses.

[Mark Rinker]

Ummmm...read elsewhere on the topic of Duramax fan clutches. If you replace the one (2002 LB7) you have with a newer unit, the new unit's engagement point will be at a higher temp.

The fan clutch in my 2004 C4500 worked fine. However, the A/C overpressurized and blew out the refrigerant on a hot day, idling in the driveway with no airflow over the condensor. (Also, sitting at idle, I have NEVER heard a Duramax fan clutch engage...which blows the theory of your A/C guy.)

Unless you know that the fan clutch is inoperable (i.e. overheating while under load or towing) I would assume it is still functional. The rate of failure isn't high.

However, if you do decide to replace the your fan clutch, I'll buy your old unit (working or not) for $50+reimbursement for UPS Ground shipping.

[DmaxMaverick]

FYI, I took it to an A/C place right before closing time. They said it sounded like a classic case of a faulty fan clutch causing the system to overheat and over pressurize.

They said replace the fan clutch, evacuate and refill the R134a and it should be good as new.

Dealer wants $259.74 just for the clutch!!!!

Cabin filter is new, I replace them twice per year.

Thanks for all your responses.

Are you sure he didn't mean the A/C compressor clutch? Replacing the fan clutch requires NO handling of the A/C system. Also, the A/C clutch can be replaced without evacuating the system. If your refrigerant is up to weight/pressures (when it does work properly), there's NO reason to open the gas system, at all.

As Mark said, too little air passing through the condenser can cause issues with overpressure. Long/hot idle periods or slow city driving can cause the same issue. Try driving in town with the T/H engaged. This will increase engine RPM's between stops, which also allows the fan to move more air. This is what I do when the temps are 100+, and it stays cold. Also, doing this, I haven't noticed a hit to mileage.

[Duramaster]

On the models that do have the the cabin air filters can they be removed with out any ill effect? They restrict air flow even when new,get dirty quick,expensive for what they are and I feel like they are not letting my system operate at full efficiency.

I actually like the cabin air filters. Have you seen the debris that they filter out of the HVAC box. With out the filters in place, all that garbage just goes right into the Evaporator core. My 1998 Suburban is suffering from this :(

[More Power]

I have a 2002 D/A with 147,000mi and never had any A/C issue until the end of last summer.
On a 95+ degree day last year, I start my truck after it had been sitting for several hours, turn on the A/C and almost immediately I see a cloud of smoke (freon) coming from underneath the hood accompanied by a loud hiss. Immediately my A/C starts to blow hot air. I shut the A/C off and figured my clutch or compressor just burned up. It was Sept so I said screw it, I'll wait until next summer to fix it. During the winter I used by defroster and noticed the compressor kicking on and off making me realize that the compressor and/or clutch must be ok. So a few months ago and went and purchased a $29 can of R134A with the gauge attached to the can. I filled the A/C system until the gauge was in the green and immediately the A/C was blowing cold air like brand new. Awesome! Then today the same thing happened.
After the truck had been sitting, I start it up, turn on the A/C which was blowing cold air....then I see smoke (freon) coming from under the hood. Without hesitating I shut of the A/C.....waited a few minutes and turned it back on...it started blowing "cool" air but not as cold as normal.

What's going on??? Do I have a blockage somewhere? Is there some sort of pressure relief valve that is opening up and allowing the R134A to escape? Is my compressor and clutch going out? How do I fix this?
Should I take it to a chevy dealer or just a reputable auto A/C place?
Thanks!!!!!!!!

The relief valve can/will vent if the orifice becomes clogged (ice or debris). Since yours works OK sometimes, the orifice is probably icing. You should have the system evacuated to extract any moisture, then recharged.

Jim

[nlp]

A reply from another board....

As an auto A/C tech, I would also agree that the fan clutch is not doing its job at the proper time and temp. Also before this occured, did you notice that the A/C system seemed to lose some of its cooling ability at slow engine speeds, particularly at stops. This is one of the main hints of failing fan clutch. Replacing the fan clutch may well put your truck back to cooling, but I would also replace the high pressure relief valve at the rear of the compressor. Delco # for the valve is 15-5711. This valve is used in many of the GM compressors. One from a junked out GM compressor will work just as well. Many times these relief valves open and then for some reason become weak and will open at a much lower pressure than designed for.

By design the high pressure switch should shut the compressor off before the relief valve opens, but for some reason this is not happening on your truck. This is the reason I would suggest replacing the relief valve before recharging.