2018 Tahoe RST AC Not working (yes another thread, but different story)

[09 LTZ]

Hi all, I have a 2018 Tahoe RST that the AC stopped working on this spring. Could see some evidence of the Condensor crack and no pressure in the system so I went ahead and replaced the condensor, put a vacuum on it for 30 minutes, checked out good, and recharged the system with R1234yf and 2 oz of oil. Worked great. For about 2 days. Now it works some times and won't engage the clutch others. The intermittent proper function tells me the system is not leaking, the belt is there, and that the compressor is not locked up or incapable of running, but now we are into the dreaded intermittent electrical issue land....

I gave in and brought it to the dealer. They verified I had put in the proper amount of refrigerant (I was actually 6 grams short, but for 802g total, the tech agreed that is not going to cause it to fail to turn on the clutch). He put dye in it and checked for leaks and none were found. Pulled codes and no BCM codes. Still failed to engage clutch at one point for the tech. The tech did some troubleshooting and after a while came in and said that the issue was the compressor itself and that it took so long because he was searching for the relay for the system but could not find it because it does not have a relay (??). He said he tested and there were 12 volts at the compressor so it has to be the compressor failing to turn on.

I am not sure I entirely believe that. I am fairly well versed in working on cars but I don't have the scantools and schematics and experience with something this new. When I drove it out of the dealer it was working fine again of course and did so for a few more days, but now it did not work all day today.

Does anybody have any experience with the same type of issue? Or does anybody have the wiring diagrams for the AC compressor system so I can try to track down the connections and relay? I have only checked the fuse under the hood with it not working and it is good, but that is not really telling me much.

Appreciate any help and insight!

 

[Tahoe14]

I'm guessing AC relay and hoping someone will chime in to verify if one exists and where it is located.

 

[Thrust]

I had a relay on the 2008 Escalade that went out. It was under the glove box area. Not sure in the 2015+ where or if they have one. Maybe someone with a service manual can tell us.

 

[09 LTZ]

Well, I spent the better part of the afternoon searching for schematics and details of a relay with no luck. Not much evidence out there of an epidemic of compressors failing like this, but some people seem to have ended up replacing the compressor after doing the condensor as well. Maybe if the system is exposed to air for many months like mine probably did over the winter it does something to the compressor clutch or pressure sensor.

I, unfortunately, don't have a lot of time here with the temps climbing and a pregnant wife and summer road trips looming. I went ahead and ordered a compressor and will put that on later this week. I hate shotgunning parts, but this was $280 shipped for the compressor and Expansion Valve (figured now is the time....). The second fill of refrigerant will hurt if I have to just let it out and refill, but maybe I can get the dealer to pull the refrigerant and recharge it for a reasonable rate.... Feels like they will want to charge just as much as another 802g of R1234yf costs though....

 

[09 LTZ]

Update.

Put in a new ACDelco compressor. When filling I could not get it to turn on the compressor so I jumpered 12v to the compressor via backprobing the connector (so all of the factory wiring was fully connected) and it came on, pulled the refrigerant in. Got it full, everything looked good. Turned it off, turned it back on, that worked. Shut off truck, let sit for a few minutes, started truck back up, AC works. Turned off and back on again, all good.

This morning the wife takes the truck and says the AC quit some time early on in her ~40 minute drive. Did not work all the way home. Got the truck home and put the gauges on and it had 100psi without compressor engagement so most likely has all of its refrigerant, no visible leaks (dealer put dye in it when it was in there).

The only thing left I could think of was to try the pressure sensor on the high side line off the compressor (the compressor came with a new variable displacement solenoid already in it). Picked up a new ACDelco pressure sensor and swapped that in. Turned on AC and it initially did not engage the clutch. Then after ~1 minute the compressor came on and ran fine, nice cold air. Turned off AC, turned it back on, no compressor engagement. I pulled the connector at the compressor clutch and checked it with a test light and no voltage is present. I tried a few on/offs of the button on the dash and the truck but no dice, compressor will not engage. Fuse is still fine.

I currently have the positive battery cable pulled and am going to let it sit for an hour or more and then reconnect and see if that does anything.

I am about to light this flipping thing on fire.

Any ideas?

 

[Jeff_]

No ideas, just wanna say reading this is frustrating because I’ve been in those shoes many times chasing down an issue.
Hope you get it resolved soon. Maybe take it to an a/c shop? Likely they could chase down the issue and you could still fix it yourself.

 

[AZRiverRunner]

Man, that sucks, I've been there, dealing with a rare, under documented problem on a vehicle. I haven't had any issues with my 2018 RST yet. I've got about 64k miles now.

There is a recall that may include your Tahoe, if it was manufactured in 2017.. https://static.nhtsa.gov/odi/tsbs/2018/MC-10145171-9999.pdf

For future reference, this bulletin also notes that "General Motors vehicles are manufactured with fluorescent dye installed in the A/C refrigerant system."

Hope this helps.

 

[Slade9699]

Dude, I have a 2018 Tahoe with 55,000 miles.... AC Quit working. Local AC guy doesn't have the tools to work on the 1234yf system.... so living in a rural area without much choice.... took it to dealership.... they said the rear AC lines are corroded and quoted me a $1600 price to fix. I'm not only pissed off, but extremely surprised that this has happened. I've always had good experiences with GM products my entire adult life... WTF can I do to keep from having to do this in another 4 years? Should I get a second opinion? Has anyone had similar issues?

 

[09 LTZ]

Update (Final, and root cause identified):

I figured it out. After having it run intermittently a few more days I settled on the idea that it must be a relay type issue. I finally found a good schematic for the truck and it showed that there is indeed a relay (labeled as K8 in the schematic) for the AC compressor clutch. But the relay is soldered onto the underhood fuseblock and not serviceable on its own. I tried a method I have used many times to test for a relay that is sticking/not engaging/etc. and tapped on the side of the fuseblock with a screwdriver handle in the area where the relay is located on the fuseblock circuit board and the clutch engaged after a few taps briefly. It wouldn’t stay on though.

The schematic also showed that there is a test pin (has a TP1 molded into the fuseblock next to it, as in “Test Pin 1”) built into the fuseblock to test for 12v on the output side of the relay which would also be a place where you could jumper 12v to the compressor and make the clutch turn on if all other parts of the electrical system were working properly. I jumpered 12v to that pin and the clutch engaged every time.

So I picked up a fuseblock (one of the local dealers had it in stock) and it works perfectly now. Has been fixed for almost a month now.






So there is indeed a relay, and my guess is it is not an uncommon failure. Especially given how small the relay is compared to other relays soldered to the fuseblock circuit board.

I hope this helps somebody else when they run into this.

 

[AZRiverRunner]

09LTZ - Thank you for posting all this great info!