11 Chilling Reasons Your Car Heater Is Blowing Cold Air

Is your car heater cranked up to the max but blowing cold air?
Or is it not working at all?

It could be broken heating controls, a heater core issue, trapped air in the cooling system, or other car heater problems.

To avoid turning into an icicle and save your engine from potential catastrophe, let’s explore the causes, diagnosis, and other related aspects involved.

This Article Contains:

11 Prevalent Causes of a Car Heater Blowing Cold Air
How to Diagnose a Broken Car Heater?
How Much Does a Car Heater Repair Cost?
4 Car Heater FAQs

Let’s get your car’s heater blowing warm air again.

11 Prevalent Causes of a Car Heater Blowing Cold Air

Here’s why your car heater could be blowing cold air:

1. Low Coolant Level

Typical heating systems use coolant (glycol and water) to absorb engine heat and warm the cabin. And over time, vehicles can run low on engine coolant or experience coolant leaks.

Low coolant means less heat absorption, which can prevent the heater from blowing hot air. It can also lead to your engine overheating. So, the next time you notice you’re running low on coolant, be sure to check for leaks in the coolant system, like the radiator, radiator cap, hoses, and water pump.

2. Broken Thermostat

The thermostat opens to release coolant when the engine reaches an operating temperature threshold. Because of that, a broken thermostat is one of the common reasons the car heater malfunctions. It can get stuck open or closed, but a stuck-closed thermostat is what typically causes the car heater to blow cold air.

For example, when the faulty thermostat remains shut, it prevents the coolant from flowing into the radiator. This also keeps the hot coolant from reaching the heater core. Not only that, it can also cause overheating.

3. Air in the Cooling System

Air bubbles in the cooling system can disrupt the coolant flow, preventing heated coolant from reaching the heater core. Insufficient engine coolant flow means the heater core can’t properly heat the air passing through it.

Air bubbles can enter the system during a coolant change, a coolant leak, or through a faulty radiator.

4. Clogged Heater Core

The heater core is similar to the radiator. It uses hot coolant from the engine to heat the air passing over it. The heater fan then pushes the warm air into the cabin.

Unfortunately, the heater core’s tubing can get clogged with debris. When this heater core issue happens, the hot coolant can’t flow through the tubes to create warm air.

5. Jammed Blend Door

Your car’s heating system contains a flap called the “blend door,” which allows hot air from the heater core to enter the cabin.

When it’s blocked, cool air bypasses the heater core and enters the cabin unheated. This can happen due to debris build-up or problems with the blend door actuator, causing your car heater to blow cold air instead.

6. Broken Heating Controls

Two heating system control issues cause your heater to blow cold air:

Broken or jammed heating control buttons
Malfunctioning heater control valve

The heater control valve adjusts the amount of hot coolant flowing to the heater core. If it’s not working, there may not be enough coolant to heat the cool air that blows into the cabin. This valve can either be mechanical or electronic.

7. Clogged Cabin Air Filter

The cabin air filter prevents dust and debris from entering the vents. Over time, the dust and debris will build up and eventually clog up the filter. A clogged filter restricts the flow of air over the heater core, and you’ll notice that the heater isn’t working at all.

8. Damaged Water Pump

Another cause of your heater blowing cold air is a damaged water pump. A faulty pump can’t create enough pressure to circulate the coolant through the cooling system. Because of this, insufficient hot coolant reaches the heater core, causing the heater to blow cold air.

9. Blower Fan Issues

Next, issues with the blower fan can also be responsible for your heater not blowing warm air. The blower fan is in charge of ventilating warm air from the heater core into the cabin vents.

There are various reasons why the blower fan might not be working, like a blown fuse, a damaged blower motor, or a broken fan blade.

10. Radiator Problems

The radiator regulates the pressure inside the cooling system by cooling down the hot coolant that passes through.

Radiator issues, like a broken radiator cap, leaking hoses, and blockages, can prevent coolant from reaching the heater core. This reduces the pressure inside the cooling system, and the heater blows cold air into the cabin.

11. Electrical Problems

Electrical issues such as short wiring, burnt fuses, and broken switches can also be why the car heater isn’t working. That’s because such faults can prevent the flow of electricity to the heater.

Now that we’ve looked at the causes of a car heater blowing cold air, let’s get you defrosted with some diagnosis tips.

How to Diagnose a Broken Car Heater?

There are several ways to diagnose a car heater problem. Typically, a mechanic would:

Inspect the coolant level and quality: They’ll access the coolant reservoir to see if the coolant level is below the guide mark or discolored. They’ll also also check for signs of a coolant leak.

Check the engine temperature: Using an infrared thermometer, a mechanic will determine if the engine temperature is normal (190-220℉). If outside the normal operating temperature, there’s likely a faulty thermostat.

Inspect the heater core: The mechanic will open the heater box and look for signs of a plugged heater core. If the heater core is clogged, they’ll flush it with air or water.

Evaluate the water pump: They’ll check all the cooling system parts, including the cooling fans, pump seals, radiator, and water pump pulley. They’ll also check the coolant flow through the system. Poor or no coolant flow may indicate a water pump issue.

Assess the blower fan: If the air conditioning fan doesn’t engage properly when on the maximum setting, it’s likely an electrical issue. They’ll locate the problematic component using the multimeter.

Flush the cooling system: If there aren’t any problematic components, a mechanic may flush any trapped air from the cooling system using a vacuum coolant filler.

Inspect the blend door: If the blend door is blocked, clearing the debris would likely fix the issue. However, several components could be affected.

Assess the heater control buttons and control valve: The mechanic would engage any controls and replace them if broken or jammed.

While diagnosing the car heater problem, a mechanic will repair or replace the problematic heating system parts. Let’s look at the costs.

How Much Does a Car Heater Repair Cost?

Repair and replacement costs depend on the affected part of your car’s heater system as well as your vehicle’s make and model.

Here are some cost estimates (including labor):

Coolant flush: $100 to $150
Fan blower motor: $150 to $350
Thermostat: $70 to $520
Blend door: $150 to $550
Heater control valve: $470 to $500
Radiator: $200 to $1200
Water pump: $680 to $810
Heater core: $800 to $1000

Now that you know the costs, let’s satisfy your other curiosities.

4 Car Heater FAQs

Here are answers to some questions you might have about car heater issues:

1. Do Heater Problems Need Urgent Attention?

You should take your car to a mechanic immediately if your car heater isn’t working.

Certain issues like a coolant leak or cooling system blockage can cause engine overheating, which incurs high repair costs and may even put you in danger.

Other causes, like a faulty blower motor, won’t heavily impact your vehicle — you’ll just have air conditioner issues. However, if you’re driving in freezing temperatures, you need a working heater to stay safe too.

2. How Does a Car’s Heater Work?

Most cars have a liquid-cooling system, whereby coolant flows through the engine, absorbing heat. Some of this heated coolant moves to the heater core. When you turn on the heater, the air pushes over the heater core, eventually reaching the cabin.

3. How to Prevent Car Heater Problems?

Maintaining your car’s cooling system through regular servicing is the best way to prevent car heater issues. Your vehicle’s recommended routine maintenance schedule indicates how often a service is necessary. However, a good rule of thumb is servicing once a year.

4. What Are the Other Signs of a Car Heater Not Working?

Other than the heater not working at all or only blowing cold air, you could also experience:

Odd smells coming from the vents
Fogging windows or steam coming from the vents
Coolant running out faster than normal
Fluctuating car temperatures (overheating or too cold)
The passenger compartment stays cold

Rev up Your Car’s Warmth With AutoNation Mobile Service

A malfunctioning car heater can stem from various issues, like a low coolant level, a broken thermostat, or heater core problems. Regular maintenance and prompt attention to the warning signs are crucial for ensuring you don’t get frozen stiff while driving through the snow.

Noticing the signs of a car heater blowing cold air?
AutoNation Mobile Service will have your cabin feeling warm and cozy in no time!

We’re a mobile auto repair service that offers efficient online booking and is available seven days a week. We also provide a 12-month | 12,000-mile warranty on all repairs.