I'm not sure if this would be considered an HVAC failure. At the end of June 2020, this was two weeks after my Model Y was delivered, I started noticing a yellow stain on the floor of my garage in the area under the front of the Model Y just behind the front wheels. I scheduled a service appointment; Tesla Mobile Service came and determined that the HVAC compressor oil was the source of the yellow fluid that was leaking. I continued to drive the Tesla for short trips only, the compressor oil continued to slowly leak. Tesla requested that I contact Roadside Assistance and have the vehicle towed to the service center. This was one way to ensure that the vehicle would be looked at promptly. (Vehicles towed to the Service Center are supposed to be evaluated within 24 hours.)
I had to rent a vehicle for 4 days until I was able to secure a Tesla Model S loaner vehicle. Tesla had my Model Y for a total of 10 days including over two weekends. Tesla Service updated me several times regarding the status of the repair to my Model Y. Multiple parts needed to be ordered so that faulty parts could be replaced (this did not include replacing the HVAC compressor.)
After Tesla completed the repairs I picked up my Model Y and noticed that the Model Y continued to drip compressor oil. Compressor oil continued to drip from my Model Y, slowly, for two more months before the ocassional drip finally stopped. I believe that the compressor oil that continued to drip from my Model Y after Tesla completed the repair was compressor oil that had earlier leaked onto a cross member or the under body panel. The problem has not recurred. My HVAC never stopped working and there were no error codes.
If you ever see fluid on the ground or the floor of your garage where you park your Tesla vehicle know your Tesla fluids:
Tesla coolant: Blue (Probably the most common fluid to leak in a Tesla)
Drive unit fluid: Red (Uncommon for this fluid to leak as the drive unit is sealed for the life of the unit.)
Brake fluid: Clear to pale yellow when new (Look for leaking brake fluid at the wheels or by the master brake cylinder)
Washer fluid: Color can vary but the most common premixed washer fluid contains a blue dye.
HVAC compressor oil: Fluorescent Yellow (like a yellow tennis ball), the compressor oil will glow faintly under a ultraviolet (UV) black light.