NHTSA Complaint #11498205 — 2018 TESLA MODEL 3

Cabin heating unit failure during winter with temperatures in the 10-20F range, loss of front window defrosting/defogging leading to poor visibility. Problem was confirmed by dealer and heating unit replaced at dealer service center, dealer now has possession of the broken heating unit. There were no indications that the unit was about to fail, until it stopped making hot air and reported a "climate system fault" when trying to select heat/defrost, it stopped working while the car was in use. The heating system stopped working around 12:30 on Friday and did not work all day, tried rebooting the head-end computer to no effect. Started working at 9am the next morning for a few hours, but stopped working while driving around 12:30 again and didn't work for rest of day, worked for an hour or so the next day and again an hour or so the day after that. The vendor was able to get an appointment on Monday to replace the unit and had the part in stock so this was failed from Friday mid-day to Monday afternoon, the new unit is installed and is now working so far. As far as I know, the heating in this model is a simple electric resistive heating element, so it is not clear to me how it could fail without a manufacturing or design defect, the car is only 3y old.