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Heat Stopped Working In My Car! Blower Motor or Resistor?

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  1. step : Verifying the Malfunction (0:20)
    • Turn on the vehicle
    • Turn on the AC or heat
    • Adjust the fan speed
    • If there is no air from the vents, or the speed cannot be controlled, proceed to the next step.
  2. step : Checking the Fuses (0:24)
    • Locate your vehicle's fuse box
    • Refer to the fuse legend or the manual to locate the blower motor fuse
    • Remove and check the fuse for damage
    • Alternatively, use a test light to check the fuse and circuit
    • If the fuse was burned out, continue with diagnosis, as there could still be problems with the blower or resistor
  3. step : Diagnosing the Blower Motor (1:10)
    • Locate the blower motor, usually under the passenger side dash
    • Disconnect the electrical connector
    • Turn the vehicle power and heater switch on
    • Use a test light to verify the ground and positive at the wiring harness
    • If positive and ground are good, the issue is likely the motor and it should be replaced
  4. step : Diagnosing the Resistor (1:59)
    • If the positive or ground were not good, proceed to diagnosing the resistor
    • Disconnect the resistor module electrical connector
    • Use a test light to verify positive and ground coming to the resistor
    • Use a multimeter to verify voltage changes from the fan speed dial
    • Reconnect the resistor module
    • Use the test light to verify the voltage changes occur at the blower motor electrical connector
  5. step : Malfunctioning Parts Affecting Each Other (5:03)
    • A worn out or malfunctioning blower motor could cause a resistor module to burn out
    • A malfunctioning resistor module could burn out a blower motor
    • If you are replacing one unit, it's best to replace the companion unit as well

Did your heater stop working? Or your AC? Chances are it's your blower motor, or it could be your resistor. That's what we're gonna talk about in this video.

So, you've confirmed that your heat or AC is not working. You've turned the key on. You've checked the heater controls. Nothing's happening. First thing we want to do is check the fuses.

All right. We want to check our test light first. Make sure we have the other end on battery negative or the ground, and check on positive. So, it works. Now, you're gonna want to check your owner's manual to check where your fuse is. So you can check the fuse on one side, and then check the other side. And as long as the test light lights up, then the fuse is good. Or you could pull out the fuse and take a look. There is little holes on the fuse, on the back side of the fuse that gives you the ability to test it with a test light.

So if your fuse is blown, just put a new fuse in it. You should be all set. Mm...not really. There's probably something else wrong with the vehicle. But let's say the fuse is good. Let's check out the blower motor.

So, you want to locate your blower motor. The blower motor generally is underneath the dash on the passenger side. And then, disconnect the connector. Every blower motor needs power and ground to work. That's what we're gonna test for. Make sure your key and your heater switch is turned on before you start this test.

So, we can test this connector. Find something metal. So, we have power there. Now, if you were to check for ground, we would want to put this end on battery positive. So you'd go to the battery on the positive terminal, and then check the other end.

So, you have power and ground at the connector, that means everything in front of that connector is working. The problem is with the blower motor, and it needs to be replaced. So if you didn't have power there, or you didn't have ground there, the next step, we're gonna test the resistor. The resistor is what controls the blower motor speed by restricting electricity through either the ground or the positive side of the circuit.

So, this vehicle actually has a resistor module. That's a little bit different than a regular resistor. It's gonna be close to where the blower motor is, and we have four wires going into this. We have one wire right here that is the blue wire, it's gonna be the power wire going into the module. This black wire right here is gonna be the ground wire going into the module. And then this lighter blue color, thinner wire is the signal wire. That comes from the switch itself. That tells the module what to do. And then, this green and black wire goes to the blower motor, and that's gonna vary the ground signal. So, what we can do is disconnect this, disconnect that. The back side has a heat sink. That's to keep it cool.

We have our test light. We have it hooked up to a ground on the other end. With the key on, I can test for power there. We have power there. That's good. Now I have the other end of the test light attached to battery positive. Now let's check this ground, and that lights up, so that ground is good.

Now I'm gonna test the signal wire to make sure that everything that is getting to the module needs to get to the module to make it work. So for this vehicle, this signal switch actually changes the ground signal. So to test the ground signal, I'll put the positive terminal on the blue wire, which is battery positive, and this ground wire to that signal wire, And then we can vary the switch. As we change the switch we can watch the voltage change. It's gonna go up.

Now, every vehicle is gonna be a little bit different, and it's gonna be hard to find these readings in different repair manuals and stuff. As long as you see the voltage changing, then you're gonna know the switch is most likely working properly.

Now, if this resistor was working properly, this was plugged in, what you could do is check the circuit on this side, and have the other side of the test light on battery positive. We're gonna vary the switch. Because we changed the switch, we can watch the light go from dim to bright. So, that is varying the ground signal and sending it to the blower motor. That's how a good resistor would look.

So, if the resistor or resistor module is not getting what it needs to, to vary the speed of the blower motor, there may be another issue with either the wiring or the switch itself, or even a relay.

So, sometimes you're gonna need a blower motor, sometimes you're gonna need a resistor. Certain instances you're gonna need both. If the blower motor itself, when it's getting its power, is having a lot of trouble, if the motor itself is tired inside, the brushes aren't doing their job as well, it's gonna put a lot of strain on the resistor. And the resistor is gonna get hot. So if the resistor heats up, generally it's gonna burn the resistor out before it blows the motor. So when you go to replace the resistor, you're gonna have a brand new resistor in there, getting really hot. After a month or two, it may burn your new resistor out.

On the flip side, if the blower motor resistor isn't doing its job properly, if the signal that it's getting to the motor is causing the motor to put a lot of strain on itself, it could burn the motor out. Not as common as the other way around. So, if you have a bad blower motor, chances are the resistor's not far behind. If you have a bad resistor, chances are it's due to the blower motor, so it's a good idea to replace them both at the same time.

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Tools needed for replacement:

    Diagnostic Tools

  • Test Light
  • Multimeter

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