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

[BBaker101]

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.

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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.

Hey is your ac still good?
Would there be any other reason to why the relay would fail.
We have this exact same issue seems like it will never go away. We replaced this fuse box and we were good for like 4-6 months probably because it was winter but the ac worked during that time when we needed it. Then it started to stop working every other month now. Then like a year later our ac has stopped working completely.
So now I'm wondering if the relay will wear out if another issue is not fixed.
We took it to the dealership they said our condenser has a small leak. But just doesn't make sense if it has a leak why would the ac work randomly then not randomly? We can literally hear the compressor kick on when it feels like to turn on that is when the ac will start working again.
The dealership wants like $1200 to fix the condenser coil and I'm just worried that putting all that money in it still won't work. When it is more electrical and the stupid relay.

 

[RST Dana]

Hey is your ac still good?
Would there be any other reason to why the relay would fail.
We have this exact same issue seems like it will never go away. We replaced this fuse box and we were good for like 4-6 months probably because it was winter but the ac worked during that time when we needed it. Then it started to stop working every other month now. Then like a year later our ac has stopped working completely.
So now I'm wondering if the relay will wear out if another issue is not fixed.
We took it to the dealership they said our condenser has a small leak. But just doesn't make sense if it has a leak why would the ac work randomly then not randomly? We can literally hear the compressor kick on when it feels like to turn on that is when the ac will start working again.
The dealership wants like $1200 to fix the condenser coil and I'm just worried that putting all that money in it still won't work. When it is more electrical and the stupid relay.

Ok #1, if your condenser has a small leak, it is no better than a condenser with a big leak
#2, find a new dealer
#3, get your condenser replaced, problem solved!

 

[Seanslane]

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.

Where does it say that in the bulletin? Because that part number for the R1234yf states it has no dye. It seems very hard to imagine Chevy is going to go out of their way to add it. Any help pointing me to where it says that would be great. I’m trying to find a leak and need to know if it in fact has dye already ty

 

[PG01]

Where does it say that in the bulletin? Because that part number for the R1234yf states it has no dye. It seems very hard to imagine Chevy is going to go out of their way to add it. Any help pointing me to where it says that would be great. I’m trying to find a leak and need to know if it in fact has dye already ty

 

[Seanslane]

View attachment 461185

Thank you. Right next to the snake bite kit. Haha.
Service guy at GM said they didn’t add it. So over GM

 

[09 LTZ]

As a follow up (a few years late, but might still be helpful to somebody), AC has worked flawlessly since the fuse block replacement. At 120k miles now.

 

[Seanslane]

Tha

As a follow up (a few years late, but might still be helpful to somebody), AC has worked flawlessly since the fuse block replacement. At 120k miles now.

thats good news.
By chance do you have a link to the schematic you found? Thanks.