Car Heater Not Working? Troubleshooting Tips

Car Heater, Low Coolant, Cabin Air Filter, Auto HVAC

Car Heater Not Working? Troubleshooting Tips

Car Heater, Low Coolant, Cabin Air Filter, Auto HVACThe last thing anyone wants to do is drive around town while freezing in their car. Even short trips seem too long when your car heater is not working. Below are a few common issues that can affect the performance of your car heater. We will cover troubleshooting tips for the car heater thermostat and cabin air filter, plus how low coolant can shut down the auto HVAC system.


Car Heater Issues + Troubleshooting Tips

While there may be dozens of reasons why your car heater isn’t working, here are some common issues where you can start. First, your owner’s manual contains a troubleshooting section you should check out. If reading your manual didn’t isolate your problem, try inspecting the major components of the Auto HVAC system.

Auto HVAC System Components

An auto HVAC system stands for Heating, Ventilation, & Air Conditioning. It controls your vehicle’s cabin temperature and air quality. Here are some of the components that make up your auto HVAC system.

Car Heater Thermostat

The car heater thermostat is a temperature-sensitive valve between the engine and the radiator in the cooling system. When you start your car, the thermostat closes off the coolant from circulating throughout the cooling system. It keeps the coolant inside the engine until it reaches its ideal operating temperature (90 – 104 degrees C). Once the engine has warmed up, the thermostat opens up again, allowing the hot coolant to circulate to the heater core. If the thermostat is faulty, it may not turn on or off when needed, which can cause cold air to come out of the vents instead of warm air.

Heater Core

The heater core looks and behaves like a miniature radiator behind the dash inside the interior cabin. The coolant absorbs heat from the engine and then pumps into the heater core. Fans blow across the heated coolant and release the warmed air out through the vents. The heater core may be clogged or damaged if you smell something sweet from the vents or see antifreeze dripping onto the floor. In this case, have a qualified mechanic replace the heater core.

Heater Fan

The heater fan moves warm air into the interior cabin through the vents. The fan may be broken or defective when the heater runs and no air flows from the vents.

Blower Motor

If the blower motor is faulty, it can affect the fan speed and airflow. Check the fuse for the heater. Your owner’s manual will have the location of your fuse box (usually in or near your glove box) and tell you which fuse(s) is for your heater.


Actuators are little flaps that open and close to direct warm air into the appropriate vents (floor, dash, or defroster). Vents also bring in outside air to regulate temperature and moisture levels inside the cabin. The heater and defroster may only work effectively if the actuators work correctly.

Low Coolant

The auto HVAC system in your car relies on coolant to perform cooling functions for the engine and subsequent systems (like the heater). When insufficient coolant is in the system, it cannot be pumped adequately into the heater core, resulting in no heated air blowing into the cabin. Low coolant is usually a sign of a leak. Address this issue as soon as possible.


Most newer cars have a front and rear defroster, but they work differently.


If the front defroster is not working, clean the vents along the dash edge near the windshield. If they are clogged with dust and other debris, the airflow may be blocked. 


If the rear defroster is not working, check the fuses. The rear defroster is electric and not dependent on the cooling system. You may need to work through the electrical connections, wires, and fuses to find the culprit.

Cabin Air Filter

A dirty cabin air filter can cause musty or dusty odors from your heater vents. Old filters can seriously impede the airflow from the heater vents, even when the heater fan is on max. If you have allergies, are sensitive to mold spores, or have a sensitive nose, replace your cabin air filter with every oil change. Manufacturers recommend replacing the cabin air filter every 12,000 – 30,000 miles. 

Car Heater Repair in Plymouth Meeting, PA

If you are looking for honest and reliable Car Heater Repair, our team of mechanics at Plymouth Auto & Tire Center is here to help! Our full-service station provides complete auto and light-duty truck inspections, repairs, and maintenance services.

Make An Appointment

Call us at (610) 825-6558 or visit us online to schedule your auto HVAC system service appointment. We will check for low coolant and a clogged air filter, and inspect the HVAC System