I have a 2004 explorer eddie baur with the automatic temperature control up front and the aux. heater in the back. The fan motor in the rear isn't working. I used a test light and I am getting power to the motor and the resistor.

I figured since I am getting power to the motor that was what was wrong. I bought a new motor and it still doesn't work. Before I throw money at other new parts, are there any tips you can give me to test what is wrong.

My first thought would be the resistor is bad but I don't know how to test it and don't want keep buying parts without knowing for sure. Thanks in advance for your help.

 

you need power to the motor, and a ground ... How did you measure the voltage ? If you have a good ground, the motor should run. I worked on a chevy once that had a corroded plug on the resistor. You could measure voltage with a volt meter. but when the motor was installed, it pulled too many amps and the voltage dropped to zero due to the corrosion.

 

I like that you used a test light as that will load the system and may give some indication of a corrosion issue as mentioned by Steve above. But where you connected the test light ground is critical in this situation. Positive voltage is applied directly to the positive terminal of the blower motor. The ground lead is where all the fan speeds are determined. And the ground for the blower travels through the rear blower motor resistor, the rear fan speed control, then the front controls for the rear fan, and finally to chassis ground. If you just connected your test light to a known ground and checked for power to the positive terminal, you bypassed a bunch of the circuit.

-Rod

 

I had a hard time finding a good ground in order to get the test light to work. I ended up grounding it to one of the seatbelt bolts. Unfortunately I don't have a voltmeter so I can't test the components that way.

When I put the test light on the connections I had power from the relay to the blower and I also had power coming out of the blower to the resistor. I assumed that was correct but maybe not (sorry electronics aren't my best area).

Do you have a suggestion of where I should ground the test light? Also where should I be looking for power and what shouldn't have power?

 

Yep, put the test light across the blower motor, then try the different rear fan speed settings. If the test light doesn't work in any of the positions, you know the issue is between the blower motor and the circuit ground since you've already confirmed there is power to the blower motor positive.

If it's too difficult to safely connect the test light across both blower motor terminals, you could also connect the alligator clip of the test light to a known positive source (battery, etc.) and use the probe tip to backprobe the blower motor connection. That's assuming you are using an old school test light and not a newer style LED test light.

-Rod

 

Update, I took your advice and put the test light across the blower motor connection. I got no power at any speed. I tried back probing like you suggested but didn't have much luck.

Is there any way to test the resistor. I have the wiring diagram. There are four wires that attach to the resistor. Thanks for all the suggestions to this point.

 

On the resistor: pins 2-1 should be about 0.5 ohms, pins 2-3 should be about 1.0 ohms, pins 2-4 should be about 2.5 ohms. Obviously you need a DVOM to test, but everyone should have one.

 

I should point out that all these test light tests (and the prior voltage tests) need to be performed with the front HVAC controls set to something other than "Off". When the front climate controls are Off, the relay that allows power to the rear blower motor via fuse F1.33 (30A in the Battery Junction Block) will not be active.

The quick and dirty test would be to select the high speed fan setting for the rear fan. The high speed setting bypasses the blower motor resistor altogether. If you don't have any high speed, the blower motor resistor is at least not the only problem. It sounds like you've already confirmed that. If you had the front function set to something other than Off and there was no voltage to the blower motor on the High speed setting, check fuse F1.33. If that's good, then try swapping out the "Auxiliary A/C Relay". It probably will be the same relay as another one nearby that you can swap with for testing purposes. Just be sure to keep track of which you swapped with.

You can test the blower motor resistor with the test light too, but it's not as straight forward as using a Digital Volt/Ohm Meter (DVOM). To do this, you'll want to connect the clip lead of the test light to the known chassis ground again. Then with the rear fan control set to Off, back probe the resistor feed line (terminal 2, Orange/Red wire). If you do not have power to terminal 2, then you're not getting power through the blower motor to the resistor and the issue would seem to be with either your blower motor or the wiring between the blower motor and the resistor block since you earlier confirmed you have power to the blower motor.

If you have a bright light at terminal 2, next turn the rear fan controller to speed setting 1 (low). If the test light dims considerably, then you are getting some current flow through the resistor block to ground. If the light stays completely bright, then move the test light probe to resistor block terminal 1 (Orange/Black wire) with the resistor still plugged in. If the test light glows you've just proven that the resistor block is passing current, but the problem is between the resistor block and the rear fan speed switch ground location.

-Rod

 

Ok, that's a lot of information and should be helpful. Thanks for both of the responses. I will test some more when I get home from work tonight.

To answer a few questions, I always test it with the front HVAC on. I have also checked fuse 33 under the hood and fuse 25 and 30 under the dash. All of them appear to be in good working order.

 

Update, I was able to perform a few tests tonight. First I borrowed an ohm meter to test the resistor. I had it set to 10X ohms and put it on the three pin combinations. It went off the scale each time, maybe I didn't have the meter set correctly. It sounds like the resistor is ok though, is that correct.

I then performed the tests with a test light. I connected the clip lead to the black ground wire of the aux blower relay (without disconnecting the relay). The orange and red wire was bright on all settings and did not dim. On setting one the orange and black wire lit up.

It sounds like I have problem between the resistor and the fan speed switch. That sounds like a lot of fun to find the problem. On a side note, when I bought the explorer the previous owner had taken out the two dome lights that are in the same housing as the fan switch and pryed apart the dome light connections (why I'll never know). Maybe something is messed up in the switch housing.

I ran out of time tonight to do anymore testing. I will try again this weekend. If you guys have anymore suggestions that would be great. Thanks for your help to this point.

 

You should be okay using the black wire of the Aux relay as your test light ground.

However, if your friend is not screaming for the meter back, it will prove to be more helpful than the test light since you'll get actual voltage readings rather than relying on your ability to see changes in light intensity. In the previous list of test steps, replace the "test light clip lead" with the black lead from the multimeter, and the "test light probe" with the red lead. Use the 20Vdc scale and see if the voltage changes when changing the blower motor speed settings.

Another quick test would be to unplug the rear blower motor resistor and connect a temporary test lead from the Orange/Red wire directly to ground. If the blower motor and wiring to the blower motor is good, the blower should run at full speed with the jumper wire installed.

-Rod

 

I tried the test you described and the good news is the blower came on. Now I just have to try to find the ground problem. I plan on just tracing the wires back to the switch to see if anything is loose or damaged. Any other suggestions would be helpful. Thanks.

 

Final update, the fan is now working. I pulled the fan switch housing down from the headliner to search for a bad ground to find that the switch wasn't even connected. I feel stupid for not checking that sooner but who would have thought it was connected. Thanks for all the help.

 

Awesome, glad to hear you got it working and without needing to replace any parts.

-Rod