7 Reasons Why your Car Heater is Blowing Cool Air


Cars are machines, and like any machine, they can malfunction in strange and confounding ways. If you’re in the middle of winter and your heater starts pumping out cool air, it can be a jarring, uncomfortable, and potentially dangerous experience. A car heater that isn’t functioning the way it’s supposed to can make the cold months absolutely miserable, and you shouldn’t have to put up with that discomfort through the winter season.

There are a number of things that can go wrong with your heater. Because of the many components working together at once, any single issue can mess up the entire system. It can be low coolant, issues with the heater core itself, clogged controls, or a malfunctioning thermostat. Some heater issues can be a simple car maintenance fix, but others require a professional to look at.

It’s a good idea to get any heater issues fixed when you can, and ignoring an issue with your heating system might result in engine failure down the road.

1. Low Coolant

All vehicles use coolant, which is a mixture of both antifreeze and water. Coolant cools your engines down during the hot months, but it also serves an important function during the winter. When you turn on the heat to warm your car, your vehicle brings coolant from the engine to the heater core, enabling it to blow warm air throughout the cabin.


Whenever you start your engine and let the heater warm, it may blow cold air for a minute or two. The interior should heat. If it doesn’t, and cool air continues to blow, you should check on your coolant level. If your car has low coolant, it won’t be able to reach the heater core and circulate the warm air.

2. Issues With The Heater Core Itself

Frequently, car heater issues are cemented in a problem with the heater core—whether it’s that coolant is low or not traveling far enough to reach the heater core, or if the blower motor’s air is not reaching it, or if there’s an occlusion somewhere in the complex tubing. A simple clog or blockage can mess up the entire system and prevent warm air from blowing through your cabin.


Your heater core resembles, in essence, a compact radiator. It’s made up of aluminum or brass tubing that can carry the heated coolant in and out, and it also has dispersal fans that release the heat generated by the coolant. The heater core both defrosts and heats the vehicle, and is situated somewhere in the back of the dashboard.


If your car isn’t properly blowing warm air through the cabin but your coolant levels are fine, you might have an issue with the heater core itself. There are a few things that can tell you if your heater core is having a problem:

  • A “fogginess” inside the cabin
  • A sweet odor
  • Losing coolant faster than normal
  • Engine overheating


3. Heater Controls Are Clogged Or Broken

Like anything else in your vehicle, the machinery of your heater and its controls can go bad after years of use. If your coolant is fine, your heater core isn’t having an issue, and you have checked everything else, it might simply be an issue with the control buttons on your dash or the valve that controls your heater. 


The heater control valve is located beneath your hood and functions as a switch that turns on the heat. If that valve is malfunctioning, it could be stuck on the cold side which would mean only cool air is blowing into the cabin.

4. An Air Lock

A large air bubble can form within your cooling system if you have a coolant leak or have recently refilled the coolant. This “air lock” will prevent coolant from properly circulating through the system, and can greatly reduce the output of heat from your heater. If you suspect that there might be an air lock in your system, crank the heater to max, remove the cap from the coolant tank, fill the coolant to its proper level, and let your car idle for a few minutes. If you notice the coolant level dropping, top it off. This should effectively get rid of the air bubble, and return the heater to normal.

5. Malfunctioning Thermostat

If your dashboard thermostat is stuck on the “C” gauge even after your engine has had adequate time to heat, your thermostat could be broken. The thermostat signals to the car that the engine has warmed up, and if it’s malfunctioning it won’t be able to send the coolant necessary to heat the heater core and blow warm air. Your thermostat is an easy and inexpensive fix for any mechanic, so if this is the issue it’s a relatively minor repair.

6. A Water Leak

Leaks are common in cars, especially older cars, and there’s a good chance you have a leak in your heater if all else fails. Leaks can show up in many different spots, so finding one can be frustrating. You’ll have to check all your hoses, your radiator, and your water pump to find the potential damage. The car heater won’t work properly if there is a leak, and you might have to have a professional look over your vehicle if you’re convinced this is the problem.


7. Bad Coolant Hoses or Clamps

With the efforts of time and use, coolant hoses might become clogged, blocked, or worn down. The clamps that secure these hoses can also go bad, eventually loosening and becoming less effective. You can visually inspect these possible issues, and get new hoses and connections to refresh your system. Check the hoses on older cars, and if you notice them feeling particularly spongey, they could be on their way out. You should always immediately replace any hoses or clamps that look suspicious.


Make That Repair

It’s winter, and you shouldn’t put off fixing your heater any longer. A working, roaring heater can make the difference between a miserable winter and an enjoyable one, and if you can’t fix the problem yourself, take it into a local shop. If you’re looking for the best parts to fix your heater, PartsAvatar has you covered. 

Don’t ignore the problem! It’s best to address car heater issues as soon as possible because it can lead to bigger problems down the road, beyond your general discomfort.


About the Author: 

Kathryn Fowler


Kathryn Fowler is the Marketing Manager at PartsAvatar. She’s been passionate about cars since childhood. She loves examining different components of cars to understand their operation. Kathryn started writing blogs on automobile parts to share her love for cars and educate automobile enthusiasts worldwide.