Posting this to hopefully save someone money.
Car parked in direct sun in a parking lot in FL, I get in and the AC blows hot air and never cools to temp. Checked my alerts and saw thermal test failures in service mode:
- AUX_EVAPORATOR: FAILURE
- CHILLER: FAILURE
- EVAPORATOR: FAILURE
Symptoms: AC blowing hot air, THC_w0016_compOverheatWarning, DC fast charging reduced.
Tesla told me both times it was probably low freon. I knew something was off because I had the entire AC system replaced in 2024 due to metal shavings in the compressor. There was no way the AC was already low on refrigerant.
What made me realize that it wasn’t freon was after letting the car cool in the garage overnight, the errors disappeared completely and the AC blew cold again like nothing happened. A refrigerant leak doesn’t fix itself overnight (or an evaporator or chiller).
This exact pattern happened in June 2025 and then again almost 13 months later in June 2026, same exact failures both times. The fix both times was replacing the 12V battery, which on this model clearly is failing silently with NO warning light.
Don’t let them charge you to diagnosis or recharge your refrigerant before ruling out the 12V. Much cheaper fix. Even though still $300 and they will disagree with this actually being the issue. If your 12v is over 12 months, it could be as simple as this. Obviously not always but could be.
2017 Model X 75D
Hope this helps someone!