How to Fix It When Your Car Heater Isn't Working

To fix your car's malfunctioning heating system, 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?

Why a Car Heater Stops Working

If cold air is coming out of the heating vents even when the vehicle is warmed up and the thermostat is set to hot, 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.

If the heater isn't blowing any air, the problem is likely a faulty blower motor or electrical connection.

How to Fix a Car Heater That Isn't Working

These instructions will help you diagnose and fix a car heating system that blows cold air. If the heater isn't blowing any air, skip to the next section.

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

   Adding coolant might fix the problem in the short term. However, low coolant often indicates another problem, such as a leaking gasket or hose. If the vehicle burns coolant, it may have a blown head gasket, which can be costly to fix. Dark brown coolant indicates rust in the cooling system.

2. Check the heater core temperature. Lift the hood and check the temperature 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, a blockage might exist in the heater core. If the vehicle has a valve in one of the hoses, check its operation. A stuck valve prevents coolant from flowing through the heater core.

3. Check for debris in the heater box. If you determine that hot antifreeze flows through the heater core, debris such as leaves, pine needles, and road debris might be stuck in the heater box.

4. Switch the thermostat from hot to cold and listen. If you don't hear the blend door moving, the problem might be the blend door, linkage, wiring, or the thermostat switch, depending on the vehicle.

How to Fix a Car Heater That Isn't Blowing Any Air

If the heater isn't blowing any air, a faulty blower motor or electrical connection might be the problem. Follow these steps to fix it.

1. Check if the blower motor receives power. The only way to determine which component has failed is to grab some basic diagnostic tools, access the blower motor, and check whether it receives power. The specific diagnostic procedure varies with the vehicle.

2. If it receives power, check if the blower motor is burned out. After removing the blower, you might find a squirrel cage so clogged with debris that the motor can't operate. In other cases, a broken wire, rusted connections, or a disconnected pigtail assembly might be the issue.

3. If the blower doesn't receive power, check that the blower fuse isn't blown. A blown fuse often indicates an 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, the fuse likely failed due to age. If the original fuse is not blown, trace the problem to the source by testing the resistor, relay, and switch.