A malfunctioning car heater in the middle of winter is no good, but oftentimes the cause is pretty straightforward. Here are the five most likely reasons.

Hot coolant warms the heater core; a fan then blows air through the heater core ... and check to see if the radiator is full of coolant. If not, turn off the car, let it cool down, then fill ...

Related: Why Does My Car Heater Blow Cold Air ... using the defrost mode with a hot temperature setting accomplishes two things: The hot, dry air defogs the windshield and melts frost and snow ...

But if your heater was blowing cold air or no air at all ... If you suspect that your furnace is not working properly, the first step is to check the thermostat. Make sure it is set to the ...