GMC Yukon
 

So my Yukon has developed an interesting problem. When you start it up from being off and sitting no matter how long it will only blow semi cold air out of the AC vents. As soon as you get the truck moving and I mean even if it’s only 100 feet it immediately starts blowing out that good old GM arctic air. Blows cold as long as the truck is moving and for a very long time after you stop if you have to wait in the car while your wife runs in the store or something but after about 20 minutes of idling the temp goes back to just semi cold. Any ideas? It’s more of a nuisance thing than anything else but it’s just an odd problem to me. I’m beginning to get an intermittent knock from the AC compressor so I know it’s gonna have to be replaced sometime soon or at the very least refilled with oil but that’s not too much to ask of a 2001 Yukon that still has all its original parts and has only seen gas oil and filters in 356000 miles. Any ideas about the semicool air?

I recently had to repair AC on a 2001 GMC Sierra with 5.3. It had the oring leak out at the joint where the orifice tube goes. I could tell by the oily schmear on the passenger inner fender.

Check to see that your condenser isn't filled with bugs and leaves. Make sure your fan clutch is working properly and pulls good air at idle. Besides that, put some gauges on it and see what your pressures are.

I replaced the oring, orifice tube, hi/lo valve fittings, and accumulator. I also added a few ounces of oil to replace what would've been in the accumulator. I then evac'd and charged in just a hair shy of 3 cans. All icy now. The first time I charged it the hi side fitting leaked badly when I disconnected the gauges. So word to the wise... replace those fittings before evac/charging, or you'll be doing it twice.:mad:

Compressor knocking? Are you sure it isn't a bad clutch bearing or ac belt tension pulley? Either one is about a $20-30 part and some frustration. The compressor is much more than that.

My guess is that it has something to do with the speed the compressor is turning - idle vs. running speed.

I'm not an ASE-certified mechanic or anything, but from my experience, the poster above is correct. It's a common sign that your compressor is going out when it cools better at a higher engine speed than at idle. The higher engine speed spins the compressor faster making it work better. The knock you describe also confirms your compressor is on its last leg.

Does this thing have rear A/C? if so the rear expansion valve has been known to go bad and causing to much freon going back to compressor and cause knock.
Could also be a little low on freon causing not enough flow at low rpm, and not enough air flow thru condensor to make things work correctly.
So engine speed and vehicle speed come into play.

My 2004 Denali and my 2015 Sierra does the same thing in this hot weather. Works normally in decent weather.

Yes it has rear air that stopped working about a year ago. When you turn it on it won’t do anything. I replaced the upper console control panel but it did nothing