Help with AC

[Knipps]

Hello everyone, this is my first post and hope to find this forum helpful as I have found others for my other vehicles. I am somewhat mechanically inclined and like to try and fix most everything myself. I am working on my 2019 Tahoe Premier 6.2 4wd 96k miles.

I just got back from a road trip to TN (I’m from IL). AC acted up a bit on the ride down but after several minutes of messing with the buttons seemed to start working fine. Had no issues on the ride home. Got in the next day and ****… no air. It blows a warm-cool but no where near cool enough to keep the windows up. Now, I know nothing about ac except for my YouTube mechanics license so I have watched some videos. I put a pressure gauge on the low pressure side and the gauge shot up to the red reading about 100psi. I stopped there and figured before I get too crazy I wanted to educate myself as to what I should be doing next. The clutch seems to be engaged while the vehicle is running and I don’t hear any clicking as if the clutch is trying to either engage or disengage. From my limited research I coulb be looking at replacing the pressure sensor and possibly the compressor itself. I’ll continue my internet search and wait for some forum knowledge. Thanks. Jim

 

[89Suburban]

@OR VietVet

 

[OR VietVet]

Welcome to the forum from Oregon.

First things first. Need a complete set of gauges attached and monitor them with the engine and a/c running. When you attached at the low side valve, which one did you attach at and was the vehicle running. If not running, the low side will read higher and it is just equal to high side static pressure. When running, The low should drop and the high should rise. To know what pressures to look for, you will need to know the ambient temperature.

 

[B-train]

What @OR VietVet stated is correct on how the system works. The newest freon can escape from a gnat's ass......so correct readings will be needed to diagnose further. The fact that the compressor is running is a good sign.

When it's commanded to full cold, does the accumulator under the hood get cold to the touch and have water dripping off it? Usually you'll see plenty of sweaty aluminum by the passenger firewall when it's commanded on and working properly.

It may be worth it to take it to a reputable shop that can do air conditioning work. These newer vehicles have a different freon than the R134A and I think its now flammable (Yay!) It requires different guage connectors and has a slightly different pressure profile if I remember correctly.

If you can get guages and still want to tackle it yourself, they make those A/C recharge kits at any auto parts store. It may just be a bit low. Just NEVER get the one with stop leak! If you ever go to a shop after using that crap, it can royally F up their A/C machine.

Last tidbit before I go. The A/C controls on these are known for being flaky as well. I had a similar issue on my 2017 Denali on a trip to FL where the A/C decided it didn't want to work with a similar story to yours. We sweated our butts off for a bit and then magically after a few key cycles it decided to work again and was back to ice cold. Took it to the dealership when I got back because it had 100k platinum warranty and it ended up being that module in the dash for the climate control.

 

[Knipps]

Ok, went out and got some gauges and here are the reading with the car running with ac on and car running with ac off. Again the clutch engages with ac on and disengages with ac off. Hot and humid as balls here 92. Appreciate the info. Thanks. Jim

 

[Knipps]

Thanks again fellas. That last was a quick post. To answer some of the questions…I do not feel anything cold and there is no sweating. While watching the gauges it looked like the pressure on the low side was slowly increasing while the high side remained the same. Are the pressures off from where they should be with the conditions?? If so, what is the cause of this?? Bad compressor?? I am guessing I can rule out a leak seeing I have pressure in the system correct? Thank again for your input and patience as I try and learn this.

 

[OR VietVet]

When clutch is engaged, the pressures should not be the same.

 

[Knipps]

Pressures dropped when the ac was turned off.

 

[OR VietVet]

Pressures dropped when the ac was turned off.

They should but they should not be even when running with clutch engaged. That is why there is a HIGH side and a LOW side. I would try adding refrigerant, by a professional shop and check for leaks.

 

[BMPNUGLS]

My first thought is you may have a clogged expansion valve….if your compressor is engaging and low side pressure goes up WAY to high..with relatively no high side pressure change. Or a plugged condenser.