2010 GMC Sierra AC Issue

[jtupper]

The AC in my truck is not working as it should. I'm noticing on really hot days it's having trouble getting the cabin down to temp and not blowing as cold as it used to. I also have noticed that it blows warm air at times. It seems like it's when I'm stopped. I noticed about a year or so ago that it would blow mist (condensation?) from the vents. At first it seemed like it only happened when I had it set to fresh air and would stop when I would set it to recirculate. It gradually began to do it regardless of what setting I had it on. It doesn't do it all the time, but more frequently now than before.

I'm hoping it's as simple as adding some refrigerant, but I don't want to add it until I can verify that is what the problem is. I don't know much about AC systems, but I know I can rent some gauges at the parts house although I don't have a clue how to read them. Any advice on where to start would be greatly appreciated.

[Cusser]

1. Never add any SEALER or refrigerant containing SEALERS !!! You'll likely ruin the entire AC system.

2. Only a shop with expensive recovery equipment can pull out and weigh your R134a, the only way to tell if the system is low. Anything with gauges only is just a guess. And I'd use a real independent shop, or a real AC shop, not a Brake-O or Jiffy Lube for this. Dual-AC systems are especially complicated, like in my 2005 Yukon.

That said: most likely your system has lost some refrigerant over the years or has a leak. I'm assuming that both your condenser/radiator fans do spin when you turn the AC on. Either should be straightforward for an AC shop to diagnose.

[jtupper]

1. Never add any SEALER or refrigerant containing SEALERS !!! You'll likely ruin the entire AC system.

2. Only a shop with expensive recovery equipment can pull out and weigh your R134a, the only way to tell if the system is low. Anything with gauges only is just a guess. And I'd use a real independent shop, or a real AC shop, not a Brake-O or Jiffy Lube for this. Dual-AC systems are especially complicated, like in my 2005 Yukon.

That said: most likely your system has lost some refrigerant over the years or has a leak. I'm assuming that both your condenser/radiator fans do spin when you turn the AC on. Either should be straightforward for an AC shop to diagnose.

So would I be wasting my team putting gauges on it? I put a temp gauge on it and it's blowing about 55° at the vent, but it's working pretty well today.

Long story short, I'm between assignments right now which means no income at the moment. Is there anything I can do to try to fix this myself? Would adding 1/2 lb. of R-134a to see if there's improvement hurt it? I know too much refrigerant is as bad as too little. Just trying to see if I can DIY this for now.

BTW, I checked and both fans are working. I appreciate your feedback on this.

[Cusser]

BTW, I checked and both fans are working. I appreciate your feedback on this.

Good; important to know the fans are both working.

So would I be wasting my time putting gauges on it? I put a temp gauge on it and it's blowing about 55° at the vent, but it's working pretty well today.

Not completely a waste to put a real service gauge set on it. At about 1500 rpm one should see high pressure reading of about 260-280 psi; lower than that "indicates" low refrigerant, but is not as definitive as evacuating and weighing refrigerant. I was 100 miles from my stuff last year and used a decent loaner gauge set from Autozone.

Long story short, I'm between assignments right now which means no income at the moment. Is there anything I can do to try to fix this myself? Would adding 1/2 lb. of R-134a to see if there's improvement hurt it? I know too much refrigerant is as bad as too little. Just trying to see if I can DIY this for now.

Automotive AC systems are designed to seep a small amount of refrigerant and oil through the compressor seal. So yes, it is possible that your system has just lost a few ounces over the past 8 years, and that would be considered normal. I went through exactly that scenario last year on my 2004 Nissan Frontier: adding pure R134a restored that after 13 years of use, and is fine this year as well. So nothing wrong in adding 1/2 can of pure R134a (or R134a with UV dye and NO SEALANT) to see if that helps. If improved after that but still not perfect, I'd add the remaining 1/2 can, but no more.

[JohnHere]

If you decide to add some refrigerant, don't forget to purge the yellow (center) hose of air at the manifold gauge set. Otherwise, you'll be introducing air into the system (albeit a small amount) along with the refrigerant, which of course you don't want.

[jtupper]

So far it's looking like it was just low on refrigerant. I added about 6-8 oz. of R-134a yesterday. I noticed before I added it that the low pressure side had some frost on the line and the drier wasn't really sweating. It wasn't freezing over, just a light frost. The AC had been running for probably 15 minutes at this point. As soon as I added the refrigerant, it started sweating.

Once I bought a thermometer, I noticed the AC would blow about 40° at the vents at night before I added the refirgerant. Today it was 90°+ and it's blowing 40° to 42°. I'm not noticing it blowing warm air anymore either. I will let it ride for a week or so and see if my results change.

Thank you guys for your responses. It was a big help.

[Cusser]

So far it's looking like it was just low on refrigerant. I added about 6-8 oz. of R-134a yesterday. I noticed before I added it that the low pressure side had some frost on the line and the drier wasn't really sweating. It wasn't freezing over, just a light frost. The AC had been running for probably 15 minutes at this point. As soon as I added the refrigerant, it started sweating.

Once I bought a thermometer, I noticed the AC would blow about 40° at the vents at night before I added the refirgerant. Today it was 90°+ and it's blowing 40° to 42°. I'm not noticing it blowing warm air anymore either. I will let it ride for a week or so and see if my results change.

Thank you guys for your responses. It was a big help.

Last summer I added pure refrigerant to my never-touched 2004 Nissan Frontier AC system and then it was fine in performance and pressures looked great; it had simply seeped some refrigerant out in 13 years. Hope yours is similar situation.