Why Is My Car Heater Not Working?

The heater system is very important to stay on top of to keep yourself and your car warm. Especially during the winter months, the heater in your car is vital to stay warm as well as safe. After all, the heater also helps demist and defrost your windows. Getting heater problems sorted before it gets cold is therefore key. Luckily, there are only a couple of parts that can cause problems.

How does a car heater work?

The car heater works by using the engine’s cooling system to transfer heat into the passenger compartment:

  1. The engine generates heat as it runs. Some of this heat is dissipated through the exhaust system and the radiator, but some of it is used to keep the engine at an optimal temperature.
  2. The engine’s cooling system circulates coolant (a mixture of water and antifreeze) through the engine and the radiator to help regulate the engine temperature.
  3. It is usually mounted under the dashboard of a car, inside the passenger compartment, and looks like a tiny radiator. Coolant flows through the heater core, which heats up the core.
  4. A fan, also called a blower motor blows air over the hot fins of the heater matrix or core which transfers the heat from the coolant to the air.
  5. The heated air is then blown into the passenger compartment through the car’s vents, providing warmth to the occupants and that’s how you get heated air in the cabin!

Heater matrix

The heater matrix, sometimes known as the heater core, is one of the heater parts most prone to failure. The matrix is a little radiator that heats up the cold air from outside before it flows into the cabin. If it is clogged up with debris it will mean that it won’t be able to heat up the air passing through it enough.

Over time the heater matrix core can also start to leak due to corrosion. This too will have an impact on how much warmth it can generate. Which is not what you want in winter!

Heater blower motor

Another part to check is the blower motor, which helps to distribute the warm air into your vehicle. Over time it’s possible that the motor’s strength will weaken or fail completely. Check the different blower speeds to see if the blower strength changes. If there is no change then the blower motor or the blower motor resistor is faulty.

Finding out which of the two is faulty can be tricky and often can only be done by removing the parts. The resistor more often than not fails due to corrosion caused by moisture in the system. An increased electrical current through the part can also lead to a resistor failure. Often this happens due to a failed blower motor or one that can’t spin freely.

Why is my car blowing out cold air when the heat is on?

If the heater is on and it is still blowing cold air it is likely due to low level of coolant. There may not be enough coolant flowing through the heater core to provide heat. A simple coolant top-up should fix the issue (if there is no coolant leak).

The other issue could you be a stuck thermostat which is small valve that regulates the flow of coolant through the engine. If the thermostat is stuck open, the coolant may not get hot enough to provide heat to the heater core. If the thermostat is stuck closed, the engine may overheat. This would need to be inspected closely and fixed by a professional mechanic.

Heater inspection

If you’re not sure what is actually faulty it’s always advisable to get an inspection first. So that a mechanic can check exactly what is wrong before any parts are replaced. Remember, replacing heater parts can be quite labour-intensive. Sometimes large parts of the dashboard need to be removed to get to the parts. This can get expensive, especially if it turns out that it’s just a small electrical problem and not the heater matrix.


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