Why Is My Car Heater Not Blowing Hot Air?

If your heater isn’t blowing hot air, it’s likely your vehicle is experiencing one or more of the following problems:

• The heater core is damaged.
• The coolant is contaminated.
• The blower fan is malfunctioning.
• There’s not enough antifreeze in the coolant.
• The thermostat is broken.

5 Reasons Your Car Heater Isn’t Blowing Hot Air

If your car heater is blowing cold air, there’s a good chance there’s something wrong with it. Here are five different reasons why your heater could be malfunctioning.

Bear in mind that there’s a difference between a heater not blowing hot air, and not blowing air at all. If your vehicle doesn’t blow any air, there’s a good chance there’s something wrong with your vehicle’s blower motor.

Heater Core Is Damaged

The heater core distributes heat, blowing it into the air with a blower fan. In many ways, you could compare the heater core to a radiator because they are both heat exchangers.

If your heater core is damaged or clogged with debris, it won’t be able to generate as much heat as it used to. This can cause the fan to blow cold air instead.

Damaged heater cores often go hand in hand with coolant problems. Your vehicle may either have a low coolant level or the fluid could be contaminated. There could also be air stuck in the cooling system.

Possible Fixes:

• Regularly inspect your heater core for leaks and seal them up.
• Clean the heater core if it is clogged but still functional.
• Replace your car’s heater core if it is totally damaged.

Coolant Is Contaminated

Engine coolant prevents your car’s heating system from freezing. This fluid allows your vehicle to absorb the heat generated by the engine. The heat is then distributed throughout your vehicle to keep you warm.

Unfortunately, engine coolant is prone to contamination. Foreign substances like dirt, water, and oil can get mixed into the fluid. This alters its chemical composition, making it less effective at absorbing and distributing heat.

Coolant contamination often occurs if you don’t flush the coolant of your car as recommended by the manufacturer or if you mix different coolants together. The latter may cause chemical reactions that can cause clogging and corrosion, preventing the coolant from circulating properly.

Similarly, using products like stop leak actually causes more problems for heater cores, leading to even more coolant leaks. Stop leak has the potential to clog the heater core, the radiator, and the hoses.

Possible Fixes:

• Use the coolant recommended by the manufacturer.
• Avoid coolant that advertises itself as universal and works on all vehicles.
• Stick to one type of coolant. Do not mix them.
• Change your coolant as needed and service your vehicle regularly.

Faulty Blower Motor

The blower motor is responsible for ventilating your car, bringing the warmth generated by the heater core to the passengers. It is designed to blow air through the vents and it is the doors inside that direct the air through the heater core, or the evaporator core.

If this motor is damaged in any way, then it might feel as if your car’s heater isn’t working even if it does generate warmth.

Blower motor failure is often caused by blown fuses, a molten blower motor resistor, or banged-up internal components. If you hear grinding noises coming from your blower motor, you may need to replace it immediately. However, if you smell something burning in your blower motor, you should stop it as soon as you can and get it checked by a professional.

If you smell something burning in your blower motor, you should stop it as soon as you can and get it checked by a professional.

–Anthony Harlin, ASE Certified Master Automobile Technician

Possible Fixes:

• Inspect air filters and clean them if necessary.
• Replace broken or damaged parts like fan belts.
• Take extra care of the motor capacitor that powers the blower fan.

Not Enough Antifreeze

Engine coolant is made of two components: antifreeze and water.

Antifreeze raises the boiling and freezing points of engine coolant. This allows coolant to do its job regardless of weather conditions.

If there’s a shortage of antifreeze in the engine coolant, the heater core could freeze over and fail to generate and distribute warmth.

Possible Fix:

• Only use the coolant recommended by your vehicle’s manufacturer.

Thermostat Is Broken

The thermostat regulates the flow of coolant to the engine and the radiator. It allows the different vehicle components to run at their optimum temperatures.

If a thermostat is damaged, it has the potential to tamper with the way the temperature is regulated in your car. This happens because the thermostat struggles to either open or close. If it cannot open, the engine coolant heats up. If it remains shut, it overheats and causes the heater to malfunction.

Possible Fixes:

• Regularly use diagnostics tools to check the condition of your thermostat.
• Check if the thermostat is jammed shut by debris or broken springs.
• Repair/replace your car thermostat if its readings are off.

Signs Your Vehicle’s Heater Is Damaged

If you believe that your car heater is not working properly, it’s important to know how to recognize the signs of a damaged heater core.

Engine Coolant Leaks

One of the biggest indicators for a heater going bad is the constant loss of engine coolant. This is most commonly found in radiators and hoses. If you ever find yourself topping up your coolant more frequently, it might be time to check for a leak. After all, coolant doesn’t just disappear. The sooner this is fixed, the better.

Strange Noises

Car heaters aren’t meant to be noisy. If you hear a high-pitched whining noise, it could be a sign that a part of your heater is malfunctioning. This noise tends to come from blower fans and the motors that power them.

Another potential cause is fuse issues.

Hot Engine, Cold Cabin

Coolant absorbs heat from the engine and redistributes it throughout your vehicle via the heater. If the engine is hot and the rest of your car is cold, it’s very likely that your heater is broken and needs to be repaired or replaced.

Fog Inside Your Car

One of the clearest indicators that there’s something wrong with your heater is if it starts blowing fog or smoke inside your car. This is usually a sign that the heater core and defrosters need to be checked.

Lingering Sweet Scents

If you can smell something sweet in your car, then it’s likely your vehicle is leaking coolant at the heater core.

How to Prevent Car Heater From Malfunctioning

There are a handful of ways you can prevent your car/truck heater from not working. These include regularly checking the coolant, replacing the cabin air filter, and scheduling regular maintenance.

Check the Coolant

As mentioned, contaminated coolant is one of the reasons for a malfunctioning car heater. Make it a habit to check the coolant at least once a week to see its condition. Also keep track of its level, as leaking coolant is a sign of a damaged heater.

Replace the Cabin Air Filter

Replace the cabin air filter to ensure proper airflow. Dirt, dust, and debris could be blocking the airway and preventing the car heater from blowing air. Check your owner’s manual to see the recommended intervals.

Schedule Regular Maintenance

Lastly, follow the recommended maintenance schedule to ensure your HVAC system stays in tip-top shape. Mechanics may be able to spot issues and address them before they turn into costly repairs, so you won’t have to sit in a vehicle with a faulty heater in the dead of winter.