A/C not working properly

LOCKAMYA

MEMBER
2014 GMC YUKON
5.3L
V8
2WD
AUTOMATIC
157,000 MILES

When we first start the car the A/C runs fine. Usually after about 30-45 minutes the amount of air that comes out the vents gradually decreases until there is no air coming from any vents. Not the foot, vent or defrost area. You can hear the blower motor still running and there is quite a bit of cold condensation all around the plastic areas near the blower motor. Also, the front and rear drain valves have a lot of water draining out during this time, more than I've ever seen before.

Thursday, March 24th, 2022 AT 5:23 AM

3 Replies

STEVE W.

MECHANIC
15,233 POSTS

Your description sounds like the evaporator core is icing up. As strange as it sounds, one of the primary causes of this in automotive HVAC is a low refrigerant charge. The next is a dirty evaporator core that restricts airflow over the core. Combine these with a higher humidity and you get rapid icing in the core. As you state that the AC works good at first, I suspect the low charge being the culprit. The solution would be to use a set of gauges to measure the pressures in the system, if it is a low charge then you would recover the current refrigerant charge and then recharge the system using the amount stated on the tag on the core support sticker.

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

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Thursday, March 24th, 2022 AT 8:15 AM

LOCKAMYA

MEMBER
2 POSTS

Hey Steve, thanks for your response. I failed to mention another piece of information. This started happening towards the end of last summer so we kind of just let it go because most of the hot weather was over. A week or so ago when it started warming up here, we turned the air on, it would only blow hot air. My first thought was to try and add some refrigerant, but the system would not accept any. I then realized that the compressor was not doing anything when the air was on. I had the compressor replaced last week by a mechanic and the system was recharged. The air worked fine when we picked it up and went on short trips. From what you're telling me it seems like the longer the trip that's when it starts freezing up. I do have a set of gauges so I will check the level, but I feel like it may be one of the other reasons you mentioned.

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Thursday, March 24th, 2022 AT 8:44 AM

STEVE W.

MECHANIC
15,233 POSTS

Likely the system has a leak then. GM has had a few models that had cores that leak under pressure. Did the shop put UV dye in it? Look for that in the water that drains out, also up front at the condenser near the mounts.
As for when it starts freezing up, it depends on the state of charge. There is a sweet spot between too low to work and a low/normal charge where the system will still work but it will effectively act like a freezer coil with any moisture. What happens is that the lower charge doesn't compress as well and as it goes through the core the molecules absorb a lot more heat than they normally do because they travel slower, that makes the core flash freeze.
I would suspect it even more as the compressor replacement didn't fix the problem. But it's still possible its airflow related, that car should have a cabin filter behind the glove box. Remove it and see if it helps or not.

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Thursday, March 24th, 2022 AT 6:38 PM