Why Do Car Heaters Blow Cold Air?

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If your car heater is blowing cold air, it could indicate that there’s a problem with your cooling system, heater core, heating valves, or blower fan.
On cold days when you have to travel by car, the first thing on your mind might be turning your heater on full blast to cozy up. And then…cold air. It’s a common occurrence, but why do car heaters blow cold air?
To help keep you warm on even the coldest of days, the car insurance comparison and broker app Jerry is breaking down the potential causes and their fixes.

Why is my car heater blowing cold air?

If your car is warmed up and the heater is blowing cold air, it’s likely an issue with one of the components that make up the temperature regulation system:
  • Cooling system
  • Heater core
  • Heating valves
  • Blower fans

The cooling system

Your car’s cooling system removes excess heat from the engine, helps the engine maintain its most efficient operating temperature, and brings it up to that temperature as quickly as possible.

Low coolant level

Especially in winter, your coolant level may be too low. If so, top it off. Be sure to check under the car and inspect the hoses and clamps for leaks.
If your coolant looks murky, it may be time for a flush and replacement.

Broken thermostat

If your dashboard sensor is indicating the engine is cool—even if it’s been running for some time—then your thermostat may be broken. A faulty thermostat will prohibit warm airflow, too.
This one requires repair by a professional, so take your car to a reputable mechanic for help.

Leaking radiator or water pump

Look under your car for coolant leaks and clean up anything you spot immediately. Antifreeze is highly toxic to both animals and humans.
If you find a leak, you may need to tighten or replace the radiator cap. If that’s not it, bring your car to a mechanic to diagnose and service the problem.

Airlock

An air bubble—also known as an airlock—can form in the coolant circulation systems, especially if the system has a leak or the fluid was recently topped off. This can inhibit coolant flow and result in the car overheating, so warm air can’t circulate to your heater core.
Try this:
  • Turn the heat to maximum
  • Remove the coolant cap
  • Turn on the car and let it idle
  • If the coolant level drops, top off with more coolant
  • When the car warms up, replace the cap and drive the car to see if heat output is normal
Key Takeaway While you can top up fluids and tighten caps on your own, always take your vehicle to a reputable mechanic if you need to diagnose and fix a more complex problem.

The heater core

The heater core is a small, secondary radiator that channels heat into the car’s cabin. Signs that the core could be malfunctioning include a fruity smell, your engine overheating, and coolant running out quickly.
Do a visual inspection—debris could be clogging the core’s fins and air intake passages, which you can easily clean.
If this isn’t the case, you may need to clear the interior passages or replace the whole unit. In either case, you’ll need a mechanic.

The heating valves

There are two types of valves: mechanical and electric. If either of them stops working, there’s no way to direct or control airflow into your cabin.
If you’re handy, you can replace mechanical valves yourself. Electrical valves are complicated and require a lot more troubleshooting, so they should always be fixed by a certified mechanic.
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The blower fans

This is, quite simply, the fan that blows warm air into your car. If it doesn’t run or no air passes through (you’ll hear the fans when you turn on the system), there could be a clog or a blown fuse. Otherwise, you may need to replace the unit.
You may be able to change out a blown fuse yourself, but take your car to a mechanic for any further work.

How your heating system works

Your heating system actually works by repurposing heat produced by your engine as part of the engine’s cooling system. The cooling system is necessary for the engine to run properly, so heat is whisked away by coolant and dissipated through the radiator.
When you turn your heater on, some of that heat is diverted from the radiator to the heating core. The heating core disperses heat through a cabin air filter and into the car’s cabin—which you control with the valves, knobs, or buttons on your dashboard.
Key Takeaway Your car’s heater uses heat as a byproduct, so you won’t get warm air out of your fans if the engine is still cold.

Why you need roadside assistance

When you’re dealing with winter driving, no heat can be the least of your worries! From icy roads and snow banks to winter fender benders, the season can be a tough one for drivers.
Give yourself peace of mind with roadside assistance from Jerry. It includes up to 10 miles of towing, fuel delivery, tire changes, battery jumpstarts, and more—all for the monthly cost of a couple of coffees.
Jerry blew my mind, honestly. From start to finish, using the app took me 10 minutes and I ended up with $100 of savings a month. Best of all, customer service answered all my questions about rental car reimbursement and roadside assistance.” ––Savanna R.

FAQs

What do I do if my heater is blowing cold air?

Wait for the car to heat up. If it’s still blowing cold air after the engine is warmed, there may be a mechanical problem.

What should I check if my car heater is blowing cold air?

First, check under your car for fluid leaks. Then, check under the hood for coolant levels, clogged air filters, or any loose components. If you can’t spot anything out of place or if you detect a fruity smell, it’s best to take the car to a mechanic.
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