Electric Cars
Heat Pump Noise When Cold: Normal or a Fault?
The car makes a hum, buzz or hiss when heating in cold weather, especially at low speed.
What causes it
The heat pump compressing and moving refrigerant - this is normal. A loud grinding or metal-on-metal sound is not.
Normal heat pump sounds
- A steady hum from the front when heating - that's the compressor working.
- A soft hiss or gurgle - refrigerant flowing.
- Fan noise that rises and falls as the compressor cycles.
What to do
- Compare the sound to another identical EV of the same brand.
- If the noise is a grind, rattle or metal clang, stop using the heat pump and book a service.
- A heat pump that suddenly makes no sound while blowing cold air is also a fault - check the AC blows cold in summer.
Note
Heat pumps save 20-30% of heating energy versus resistance heaters. In very cold weather (-15°C and below), the heat pump becomes less efficient and the car uses a resistance heater as backup - that's normal and you may hear it switch.