The heater in your vehicle is a nice comfort item, and it can be very costly to repair if and when it fails. A broken heater can prevent your defroster from blowing warm air to your windshield to eliminate ice and fog.
Is it a heater core?
The heater core is one of the most common reasons your heater is not working. The heater core works in conjunction with your engines cooling system. The function of the cooling system is to remove heat from the engine by sending the heated antifreeze to the radiator located in the front of the vehicle. The position of the radiator allows outside air to blow across the radiator, cooling the antifreeze. Think of the heater core as a small radiator located in the dashboard of your vehicle. Antifreeze is constantly being circulated throughout the engine, radiator, and yes even the heater core, whether you have the heater dashboard switch on.
When the heater core leaks, it will usually leak inside the car on the passenger side under the carpet. If your heater isn’t working, or you smell a sweet odor, check the passenger side floorboard. A leaking heater core may also leave a greasy film on the inside of the windows. The common cause of a heater core leak is a rust build up caused from a lack of cooling flushes.
Is it low antifreeze/water in the radiator?
Low antifreeze levels or poor circulation of that antifreeze throughout the cooling system will hamper the heater performance as well. When you check the antifreeze level in the radiator make sure the fluids are in good shape and of proper color (either a green or orange/red).
Is it a bad thermostat?
Another cause of a heater not working is a faulty thermostat. The thermostat is calibrated to keep the antifreeze inside the engine at a constant temperature. A faulty thermostat might not allow the engine temperature to get hot enough to heat the antifreeze. Thermostats generally do not need periodic replacement. Proper engine temperature plays a vital role in fuel economy and the overall running condition of the engine, as well as regulating the cooling system temperature.