2018 GMC 1500 AC blows hot air

2018 GMC Sierra with 66,000 miles recorded - AC blowing hot air

It is out of warranty. Your choice, take it to an independent AC shop or your GM dealer. An independent shop likely will not charge you a diagnostic fee if they do the repair.
Either you have a failed (or failing) blend door activator or a refrigerant leak. Or if automated climate control the controller may have failed.
Please post back with diagnosis.

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Concur, an AC shop is usually the best solution for this sort of problem. There’s just too many failure modes to consider. If OP wants to try something on their own first, check under the hood to make sure the AC compressor and condenser fans are both spinning.

Lawsuit: Air Conditioning Systems Prone to Failure in GM Vehicles (classaction.org)

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hmmm, I wonder what the ‘defect’ is? I also wonder how the plantiffs expect to win considering the vehicles lasted through the warranty period?

probably the same as this…
General Motors Facing Class Action Over Allegedly Defective Air Conditioning Systems

Story says something “broke” in ac system to cause a leak. Good story.