Regarding warranties, back in the 1980s it was common for Subaru to have A/C units added on. This was done at (in the case of OK) at the port in Houston, TX or by the selling dealer. People thought they were getting “factory A/C” when nothing was further from the truth., I installed many of them.
The sticky part on this was that the port installed units were done in 2 man teams. One guy under the hood and one inside the car. This job was done in something like 35 minutes and the installers were paid piece work. This would sometimes result in installation issues.
The REAL sticky part and unknown to car buyers was that the A/C warranty on port installed units was 90 days. Period. This meant that if the car sat on the dealer lot for 3 months and 5 days pre-sale the warranty was up on any A/C installation. This in turn meant the dealer mechanics got hosed by having to fix port errors for free.
As for the Hyundai they are NOT going to send any Hyundai mechanics to the dealer to work on your car. They have none. They’re all at the dealer. And Hyundai is not going to do a buy back on a used car.
As Whitey correctly mentions the brand is irrelevant. Many people go through the same thing no matter the make; be it Acura all the way through to Zundapp with the latter long being gone.