Car Heater Suddenly Not Working?

Check these things first

There are many reasons why a car heater stops working. To find out what's wrong with your car's heating system and what you can do to fix it, you first need a basic read of the situation. Is the heater blowing cold air into the car, or is the car heater not blowing any air at all?

How to Fix It If Your Car Heater Is Blowing Cold Air

Illustration of a person shivering in a car and saying Brrr...
Lifewire / Maddy Price

If cold air is coming out of the heating vents, even when the vehicle is warmed up and you’ve set the thermostat to hot, then you could be dealing with one of the following problems:

  • Low coolant
  • A blockage in the heater core
  • A stuck blend door
  • A stuck heater valve
  • A bad switch or linkage

To diagnose the problem:

  1. Check the coolant level. Turn off the vehicle and let the engine completely cool down. The coolant is housed in a translucent plastic jug in the engine compartment and should have level indicators that show how full or empty it is. If the coolant level is low, then the vehicle likely isn't circulating enough antifreeze through the heater core and needs to be replenished.

    Filling the coolant may fix the problem in the short term, but low coolant often indicates another problem, such as a leaking gasket or hose. If the vehicle burns coolant, it may be a blown head gasket, which can be costly to fix. Coolant that's a dark brown color indicates that there is rust in the cooling system.

  2. Check the heater core temperature. Lift the hood and check the temperature around where the heater core hoses enter the heater core box. The safest way to do this is with a non-contact infrared thermometer. If one hose is the same temperature as the coolant and the other hose is cold, there may be a blockage in the heater core. If the vehicle has a valve in one of the hoses, check its operation. If the valve is stuck and prevents coolant from flowing through the heater core, then that is probably the source of the problem.

  3. Check for debris in the heater box. If you are able to determine that hot antifreeze is flowing through the heater core, then there may be debris in the heater box. This can happen when leaves, pine needles, or road debris are in the heating system.

  4. Switch the thermostat from hot to cold and listen. If you regulate the thermostat from hot to cold and cannot hear the blend door moving, that may indicate a problem with the blend door, linkage, wiring, or the thermostat switch, depending on the vehicle.

How to Fix It If Your Car Heater Isn't Blowing Any Air

If the heater is broken because it's not blowing any air at all, it's likely due to a faulty blower motor or electrical connection.

The only way to determine which component has failed is to grab some basic diagnostic tools, access the blower motor, and check whether or not it receives power. The specific diagnostic procedure will vary depending on the vehicle.

If you're able to determine that the blower motor is receiving power, then the blower may have burned out. You may find, after removing the blower, that the squirrel cage is clogged with so much debris that the motor can't operate. In other cases, it may be a simple problem such as a broken wire, rusted connection, or disconnected pigtail assembly.

If the blower is not receiving power, check the blower fuse to make sure it's not blown. A blown fuse often indicates a different underlying problem, so never replace one with a larger fuse to prevent it from blowing out again. If you replace a blown fuse with one of the same amperage and it doesn’t go out, then the fuse likely failed due to age. If the original fuse is not blown, trace the problem back to the source by testing the resistor, relay, and switch.