Why is my heater blowing cold air in my car?

man's hand on a car heater vent

Dealing With Cold Air

Ready or not, winter is blowing in from the north and the temperatures are getting cooler. In Illinois, the winters can get brutally cold, so a non-working car heater can make the drive to work miserable. If your heater isn’t working right, now is the time to get that heater repair done. 

Understanding how a car heater works can help to understand what happens to make them quit working. A car heater has some basic components: 

  • The heater core
  • The blower motor/fan
  • Heater hoses
  • A heater control valve
  • The HVAC control panel inside the car

Each of those components interacts with the coolant, the thermostat, the radiator, the heater core, and the water pump. As the engine warms up, it creates heat. Most of the heat will exit through the exhaust system. 

Any remaining build-up that remains inside the engine casting is transferred to the coolant. Once the thermostat opens, the coolant is allowed to cool the system by circulating throughout the engine. This removes the excess heat that did not exit through the exhaust and sends it to the radiator as it circulates through the heater core.

From there, it is distributed into the cabin of the car where it warms the interior as you have the heater controls set, with the fan blowing it through the vents. Car heater repairs can be needed with any of the components that malfunction or totally quit. 

So, what would cause the heater to stop working in a car?

There can be a number of reasons why your car heater is not blowing air. Some of the normal reasons car heaters repairs are needed: 

  • Thermostat is Faulty: One of the most common car heater problems is a faulty thermostat. They become stuck closed or open, making it unable to let the built up heat from the engine flow through as described above. 
  • Low Antifreeze: This is the second-most common issue mechanics find when working on car heater repairs. When the antifreeze level drops too low, the heated fluid can’t get to the heater core, and the cabin of the car won’t warm up. 
  • Faulty Heater Fan: If the blower motor on the fan isn’t working the heated air from the antifreeze isn’t going to be distributed throughout the cabin. 
  • Faulty Blower Motor Resistor: A broken blower motor will not allow the fan speed to work properly, maybe keep it from working at all.
  • Clogged Heater Core: This isn’t as common a heater repair need as the aforementioned items, but debris and particulates that get into the coolant system can clog the heater core. This debris and particles can come from a rusted radiator. The only heater repair for this is to try flushing the radiator or replacing the component. 
  • Leaking Radiator: If the radiator has a leak, it will keep the antifreeze from reaching the heater core and cool the engine. This can cause the engine to overheat and damage it to the point of needing a new engine. 
  • HVAC Controls: Over time the buttons, knobs, or touchscreen can malfunction or quit working. This can keep the heating system from working properly. 
  • Blow Fuses or Faulty Wiring: As with the HVAC controls, the car heater isn’t going to work properly (or not at all) if the wiring is broken or has a short. 

What is a car heater core?

A key part of your car heater working is the heater core. This component looks like the radiator but is smaller. The antifreeze coolant that is in the actual radiator is circulated through the small tubes and radiates heat from the engine throughout the cabin. Heater repairs are often getting the heater core unclogged or replaced. 

Why does my car heater not work when idling?

In most cases, when a car heater isn’t working and is taken to a mechanic, they find the heater repair was nothing more than adding antifreeze coolant to the radiator. As we described earlier, it is the heat from the engine that is needed to make the car heater work.  It needs the antifreeze coolant to move the heat that doesn’t go through the exhaust to the heater core and into the car cabin. 

How much does it cost to fix a heater in a car?

It can vary from make and model of the car and the problem found by the mechanic that performs the heater repair.  For example, the heater core or the radiator may need replacement, or the wiring may need replacement, or you could be dealing with any of the issues we’ve discussed. Most car heater repairs will start around $300 and reach up to $1000. 

temperature control knob in a car

Ending This Article With A Last Question

When your car heater isn’t working, do a Google search for “where to find car heater repair near me” and find an authorized mechanic that knows how to fix the heat in cars of your make and model. If you have a foreign-made car, you will need to take it to a mechanic that specializes in that make. American-made cars are all about the same when it comes to heater repairs. Meanwhile, if you’re in the area and find yourself in need of heater repair, you can always come to us!