Why Is My Car Heater Not Working?

It’s that time of year when we turn off the A/C and crank up the heat expecting a warm blast through the vents to shake off the morning chill. But instead, your car greets you with cold air and a fogged-up windshield. Now, you're not just battling rush hour traffic you’re doing it in a frozen vehicle.

Don't worry grab your coat, and let’s break down why your car heater isn’t working and how you can fix it.

How Does a Car Heater Work?

In most internal combustion engine (ICE) vehicles including hybrids your car’s cabin heat comes from the engine cooling system. Hot coolant is circulated through a component called the heater core, and a blower fan pushes that warm air into your cabin.

When something goes wrong with this process, the result is a chilly commute. Here’s how to tell what kind of failure you’re dealing with.

Types of Heater Problems and What They Mean

1. No Air Blowing from the Vents

If there’s no air coming out at all hot or cold it’s usually an electrical problem involving one of the following:

• Blower motor
• Blower motor resistor
• Blown fuse

Step one: Check your fuse box for a blown blower motor fuse.
If the fuse is good, the issue likely lies deeper in the electrical circuit. You could try replacing all three components, but unless you're skilled with electrical diagnostics, it’s best to bring it to a shop.

If you're not into DIY auto repair, let a trusted mechanic at ABC Auto Repair in Burien diagnose it for you.

2. Only Cold Air Blowing

If the fan works, but only cold air is coming through, this is likely a coolant circulation problem.

Your heater core either:

• Isn’t getting enough coolant, or
• Is clogged and can’t circulate properly.

This is serious. Low coolant can lead to an engine overheat, which could leave you stranded or facing catastrophic engine failure. Topping off coolant may be a temporary fix, but you'll need to find the source of the leak or blockage for a long-term solution.

Quick test: With the engine running and warmed up, check the two heater hoses going into the firewall. If one is hot and the other is cold, the heater core isn’t circulating properly and probably needs to be replaced.

This is often a messy, labor-intensive job definitely one to leave to the pros unless you're highly experienced.

3. Heat Only Comes Out of the Windshield Vents

If hot air only comes from the defrost setting, you’ve likely got a problem with the blend door actuator or blend door system, which controls where air flows in your cabin.

Good news: your engine cooling system and blower are probably working fine.

The blend doors are designed to fail in the defrost position to prioritize visibility and safety. Depending on your vehicle make and model, this fix could be simple—or it might require full dashboard removal.

Give us a call at ABC Auto Repair in Burien and we’ll let you know if it’s something you can handle, or if you’d be better off letting us take care of it.

Let’s Get You Back on the Warm Side of the Road

No matter what kind of car heater failure you’re dealing with, it’s never fun when your windows are fogged, and your toes are freezing.

We’ve got your back.

At ABC Auto Repair in Burien, we specialize in diagnosing and repairing heating system issues from blown fuses and heater cores to blend door actuators and coolant leaks.