Don’t worry, put on your winter coat because we’ll help you understand why your car’s heater does not work and how we can fix it.

How does the heater in your car work?

In common Internal Combustion Engine Vehicles (ICE) to include hybrids the cab heating system works off of the engine cooling system’s circulation of hot coolant to the car's heater core. The heat is then transferred into the cab via a blower fan.

Type of failing heater symptoms and what they mean

No air blowing from vents at all.

No air from the air vents is usually an electrical problem with the blower motor, blower motor resistor or fuse. Somewhere in this collection of three systems is a failure point that prevents the blower motor from blowing air.

The first step to fix this issue is to check your fuse box blower motor fuse. If the blower motor fuse is in good shape, not broken. The electrical problem is a little deeper. You could at this point replace the blower motor, blower motor resistor and the blower motor switch as a shot in the dark or you can isolate the problem with diagnostics.

Either way, at this point take it to a repair facility unless you’re savvy with DIY (Do It Yourself).

Only cold air blowing from vents.

When only cold air is blowing from your vents the problem is not an electrical issue but a coolant issue. Your heater core does not have enough coolant circulation to warm up the air being pushed into the cab by the blower motor.

The heater core has either clogged and is no longer circulating coolant or it has no coolant in it to circulate. Both conditions mean you can’t defrost your windows but one condition is more serious than the other.

Not enough coolant means you're losing it somewhere and if this is not addressed it could lead to an engine overheat that could mean catastrophic engine failure or being stranded with a hot engine and no cabin heat. Correcting the coolant loss or topping off the cooling system should solve your problem temporarily.

Finding and fixing the coolant loss would be the permanent fix. Poor circulation through the heater core can be detected by verifying your coolant level is normal in the radiator and the radiator reservoir. You would then need to feel the heater hoses going to the heater core. If the heater core is circulating properly, then both hoses should feel warm to the touch.

If one is hot but the other is cold then the heater core is not circulating properly and would need to be replaced. This repair is usually quite extensive and can get messy so most people have it done at a repair facility. 

Hot air only blowing on windshield

Hot air is blowing, but it’s only on the windshield. Freakin’ outstanding. This condition means that your overall engine cooling system and heating blower element is working properly.

What commonly fails the heater blend door that controls how the air is distributed through the cab of the vehicle. The blend doors are designed to fail in the windshield defrost position to ensure that your windshield would remain clear in the event of the blend failure.

Depending on the make, blend door replacements can get extensive, requiring full dashboard removal or they may be easy access. Give our repair facility a call to determine if this can be a DIY repair.

In conclusion, regardless of what type of heating system failure you’re experiencing it’s never fun on a cold winter morning.



Lucky for Des Moines, Washington we are here to correct these concerns for you quickly. From diagnosing to conducting the repairs, we’ll get you back to the warmer side of the road. Schedule your next repair with ABC Auto Repair here.