A software issue could cause a lack of heat from the cabin heating system
This prompted a safety recall due to the effects on the performance of the defrost system
Tesla says a software update will fix the problem
Many owners have complained that their Tesla equipped with a heat pump was not providing enough cabin heat during the winter.
Since this issue also affects the windshield defrost and a couple of updates have not been able to provide a conclusive solution, the NHTSA got involved.
Heat pumps are becoming more popular with EV makers since they require less energy to provide the same amount of heat as a traditional resistive heater, meaning that it allows for a longer range in cold weather, an important factor in electric vehicles.
The problem is apparently caused by the Electronic Expansion Valve (EXV) which could experience interruptions in the communication with its controller. This leads the controller to attempt to realign it by rotating it open in small increments. When some of the vehicles experience this malfunction, the controller doesn’t close the valve back, which traps the refrigerant inside the evaporator and makes the compressor enter fail-safe mode, which severely limits the heat output. The failures happen more frequently at temperatures below -10˚C.
Since the air coming out of the defrost outlet is cold, it struggles to melt the ice and to clear the frost that is on the windshield, thus making it difficult to see the road.
The NHTSA has a standard for defrosting performance, which fails to be met by the malfunctioning Teslas, thus prompting a safety recall.
Tesla says it is working on a new software fix that will force the controller to close the valve in order to stop the refrigerant from pooling in the evaporator.
