Fix the Issue of No Heat in the Car
You go to warm up your car on a chilly morning only to find that your car heater is not blowing air, at all. Our mechanic explains what could be causing that, and how to troubleshoot, diagnose, and fix blower motor and blower motor resistor issues that are probably to blame in this video:
Car Heater not Blowing Air? Blower Motor or Resistor?
Why is my car heater not blowing air?
There can be numerous reasons that your car heater is not working but if your car heater is not blowing air, at all, that could mean there’s an issue with your blower motor, blower motor resistor, or your heater control switch. Your car’s heater not working is usually a symptom of one of those issues.
What can cause a car’s heater to stop blowing air?
A car heater that’s not working can be caused by the following issues:
- Failing or blown blower motor
- Failing or blown blower motor resistor or blower motor resistor module
- Bad or blown blower motor fuse, connector, or wiring
- Broken or failing heater control switch
- Bad or blown blower motor resistor or blower motor resistor module connector or wiring
How do I diagnose and fix a car heater not blowing air?
Check the fuse
If you’ve checked your car’s heater controls and you find that nothing happens when you adjust them, you should check your fuse with a test light:
- Look up where your fuse is located in your owner’s manual so you can test both sides.
- Make sure your test light is working, and that the other end is on the battery negative or ground. Check the positive to confirm it’s working correctly (0:25).
How do you know if your fuse is working correctly? If you test it and the test light lights up, your fuse is good. You can also test a fuse by pulling it out to inspect it (0:48).
If your fuse is blown, while you’ll need to replace it, that doesn’t mean that’s the only issue that caused your heat to stop working. It’s more likely that something else is causing it.
Inspect your blower motor
Even if your fuse is working properly, you’ll want to check out your blower motor, which is usually located underneath the dash on the passenger side.
Test your blower motor’s connections
- Disconnect the blower motor connector.
- With your key and heater switch both on, test the connector using a test light. Our mechanic shows you how to test the connector’s power and ground at 1:28 in the video above.
If your blower motor connector’s power and ground are working, that means everything in front of that connector is working, which narrows down the issue to the blower motor itself, and you’ll need to replace it.
Test your blower motor resistor
If your blower motor connector’s power or ground aren’t working, you’ll need to test the blower motor resistor.
The blower motor resistor controls the blower motor’s speed by restricting the electricity through either the ground or the positive side of the circuit.
In our featured video, the vehicle our mechanic works on has something a little different, which is a blower motor resistor module, and is located near the blower motor.
Our mechanic explains each of the module’s wires at 2:23 and shows you how to test this module with a test light beginning at 2:53, and with a multimeter at 3:34.
Test your heater control switch
If the data on the multimeter shows that the module’s voltage is changing as you adjust the heater control switch, that means your control switch is working correctly.
If your blower motor resistor or resistor module is working correctly, you can then test the blower motor resistor or resistor module circuit using a test light (4:24).
Watch the test light as you adjust the heater control switch. If the test light’s brightness changes as you adjust the switch, that means the resistor or resistor module is working correctly.
If you don’t see this variation in brightness in your test light, that means the resistor or resistor module isn’t working correctly, and can’t vary the speed of the blower motor. In that case, there could be an issue with the resistor or module wiring, the control switch itself, or even with a relay.
Should I replace the blower motor and the blower motor resistor at the same time?
In one of these situations, you may need to replace either the blower motor or the blower motor resistor/resistor module, or you may need to replace both.
If the blower motor isn’t working correctly, that strains the resistor, which makes the resistor heat up, and typically leads to the resistor burning out before the blower motor fails. In this case, it’s best to replace both the resistor and the blower motor at the same time to prevent the blower motor from failing after you replace the bad resistor.
Generally, it’s always a good idea to replace both the blower motor and the
blower motor resistor together, even if you think only one of those parts has failed.