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Old 07-13-2013, 04:22 AM
Join Date: Apr 2013
Posts: 4
Default How to test your A/C Heater Blower Motor and Resistor

Crossfire Blower Motor and Resistor Bench Test

I have read just about every post on the crossfire forums about blower motors not working and for the most part everyone of them has the same solution. Throw a new resistor in and presto-magico the fan works! Well, I am not one who likes to just throw parts at a problem and see what sticks. So, with the help of a Service Manual and a multi-tester I tried to actually figure out how to be sure of the problem.

First I will say, that it appears that there is a real problem with drain tubes in the cowl area clogging up and water (especially after a car wash) getting down into the blower motor box and damaging parts. In fact this is what happened to mine.

Second, the Crossfire is highly dependent on a good battery and proper voltages at the battery and from the alternator. If you have other electrical problems in addition to no blower fan, check your alternator and battery first.

So, assuming the only problem you are working with is "no air flow, with the a/c or heat turned on," then try the following steps to diagnose the issue.

The main parts of the system, are the Blower Motor, the Blower Motor Resistor Pack, the A/C Heater Control Module, and 5 fuses.

With the ignition key in the "On" position test the following fuses:
(all are under the hood in the fuse block near the windshield on the driver's side)

15 - Listed as " Residual Engine Heat Utilization" - provides power for the "Coolant Circulation Valve and Pump" - Hot at all times - 5 amp

33 - Listed as "Residual Engine Heat Utilization" - provides power for the A/C Heater Control Module - Hot in "on" and "Run" - 5 amp

35 - Listed as "Radio Frequency Remote Control, Hazard Warning Flasher, Instrument Cluster, Climate Control" - provides power for the A/C Heater Control Module - 15 amp

36 - Listed as "Climate Control" - Hot at all times - provides power for the Blower Motor - 30 amp

37 - Listed as "Circulating Air, Instrument Cluster, Radio Frequency Remote
Control, Climate Control" - provides power for both the A/C Heater Control Module and the Recirculated Air Switch Over Valve - Hot in "On", "Run", and "Start" - 5 amp

You will notice that only one fuse is a high amperage one (36) and that it is the one that is directly responsible for the Blower Motor. If all of these test good, and there is no corrosion then you will have to move on to the inside of the car.

You will now need to pull the cover from under the Glove box to get to the blower motor. You will be removing 2 Phillips head screws, one at each of the corners nearest the glove box side of the panel.
Above this panel is the blower motor access and access to replace the Cabin Air Filter. To get at the blower motor you will need to unplug the 3 wire connector and slide two clips aside. The door will now hinge down and can be removed. There are 4, Torx-20, screws to remove to get both the fan and resistor out as a unit.

Make sure the area inside the box is clear of debris, you should also check around the Cabin Air filter side of the box to verify you don't have foreign objects causing your problems.

To test the power to the fan and from the Control Module:

Check the 3-wire connector previously removed for corrosion, the wires at the connector are Red (RD), Brown (BRN), and White with a Pink stripe (WT/PK)

RD is on one end of the connector and is the 12+ volt source from Fuse 36
BRN is at the other end of the connector and is the 12- (Ground)
WT/PK is in the middle and is the control module circuit + voltage signal

1) Testing Power to the Blower Motor
Key can be "On" or "OFF" for this test
Use a digital multimeter to test for voltage between BRN and RD,
voltage should be 12-14 volts depending on your battery voltage.
If less than 12 volts, check your battery voltage directly - refer back to the 3rd paragraph of this write up. If your battery voltage is good (better than 12.5 volts) and you still have less than 12 volts you most likely have a bad ground or shorted wire. ---- Go to "Continuity Test"

2) Testing the Control Module output
Key "On"
Using a multimeter to test voltages between BRN and WH/PK.
Fan Switch Position - Voltage as Tested
0 (switch off) - 0 volts
.5 (I have no idea what this position is for) - 0 volts
1 - 1.9 v
1.5 - 2.45 v
2 - 2.8 v
2.5 - 3.2 v
3 - 3.7 v
3.5 - 4.2 v
4 - 4.7 v
4.5 - 5.2 v
5 - 7.3 v
* all voltages can vary by a tenth or two

If all switch positions have appropriate voltages, then your Control Module is functioning correctly.

3) Testing the Blower Motor:
With the Blower Motor on a bench, remove the Resistor Pack (2 Torx-20 screws). Remove the Red and Blue wires, remember which goes where for later. (Take a picture with your phone.)

Using a DC Voltage Power Supply - (I use a modified desktop computer power supply) (Get instructions to build your own at -
*You could also use a car battery for this particular test.*

Support the fan shroud in a vice or other suitable location.
Apply the ground (12-) to the Blue wire and 12+ power to the Red wire.
The fan should be running at max speed, if not you have a bad Blower Motor.
If your fan works move on to step 4.

(My fan had rust and other problems, I used a lot of WD-40 on the spindle shaft and all the other parts and then hooked up a drill to the shaft to spin it quickly and let the WD-40 do it's job) (the WD in WD-40 stands for Water Displacement, so it is safe to spray all over the motor, brushes and all)

4) Testing the Resistor Pack
Hook the fan's Blue and Red wires back up to the resistor pack.
Connect your power supply as follows. (if you don't have a power supply with multiple voltage outputs and your Control module checked good you can connect your regulator back up to the vehicle wiring to test the Resistor Pack.)

There are three pins that the factory wiring harness plugs into on the Resistor Pack, connect your power supply ground lead to the one closest to the Blue wire. Connect a 12+ lead to the pin closest to the red wire pin. Nothing should be happening; if your fan moves or you get smoke, your resistor pack is shorted and should be replaced.

Next connect a 2-7 volt lead to the center pin; your fan should be moving at a speed appropriate to the voltage input on this lead. Compare your speed to the voltage chart above from the Control Module Test. If your power supply, like mine only has one or two low voltage outputs you can connect a resistor or a series of them to your power lead to drop the voltage going to the center pin, this should give you the ability to vary the speed of your fan. This is exactly what the resistor pack does to control the fan speed. (I used a couple of 1000 ohm 1/4watt resistors to vary my voltage.)

Now, if you got through step 3 with no problems, the resistor pack is almost certainly the offending part. But step 4 will confirm. If (like me) you make it through step 4 and everything seems to be working correctly, your problem was probably a rusty motor that was simply stuck. WD-40 and a drill to spin the motor on the bench for a few minutes fixed mine, and I only burned about one hour testing and researching everything. In fact it has taken longer to explain, than it did to do everything.

Finally, if your motor is showing signs of rust it means water is getting into your blower box and you need to clean out any debris stuck in the box and clean the cowl vent drain tubes to prevent further damage.

***Continuity Test.
A continuity test is a very simple process used to verify that electricity can flow through a particular circuit.
In our case we are looking for a bad ground or bad power lead that feeds our blower motor.
First we will check the ground:
connect your multimeter in ohms/resistance mode between the Brown wire on the 3-wire connector and the battery 12-, you should have near 0 resistance. A small amount is normal just due to the amount of wiring and body panels the power is flowing through. If you get a very high or infinite amount of resistance your ground is bad and the wire will need to be traced and repaired (look for corrosion) or replaced - you can continue the other steps in the testing process by running a temporary ground to work from, instead of the Brown wire.
Second, we will test the Power lead.
We already know that Fuse 36 is the supply for this wire, and that the fuse is good. So, pull the fuse and with your tester find the hot and dead side of the circuit. You are going to preform the same test as before except between the Red wire and the Dead side of the fuse holder. Again, you should have very low or no resistance. If you get a very high or infinite amount of resistance your power wire is bad and the wire will need to be traced and repaired (look for corrosion) or replaced.

I hope this helps a few of you save some money on parts. Good luck

Last edited by jefferyallison; 07-13-2013 at 01:44 PM.
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Old 07-13-2013, 05:37 AM
ala_xfire's Avatar
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Default Re: How to test your A/C Heater Blower Motor and Resistor

Awesome write-up !!
The only thing missing is some pictures to assist the truly electrically challenged.
I had no problem following the logic and steps, but some might require the comic book pictures to accompany the text.


Link to common problem fixes and documentation

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Old 07-13-2013, 01:31 PM
Join Date: Apr 2013
Posts: 4
Default Re: How to test your A/C Heater Blower Motor and Resistor

Ala_xfire, thanks for the comment!
I wish I had been smart enough to take a few pictures. I think I took the one that I recommended everyone take and that was it.
Maybe someone who know how do do such things could pull a few pics from other Blower Motor write ups and add them in for reference? I know in my searches, there were quite a number of good pics.
I just really hated to waste the info after I was done with it. So I hope it will help someone else out there.
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Old 07-13-2013, 05:41 PM
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Default Re: How to test your A/C Heater Blower Motor and Resistor

We need more writeups like this one.

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Old 07-15-2013, 02:55 PM
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Default Re: How to test your A/C Heater Blower Motor and Resistor

Nice write up! Thanks

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Old 07-15-2013, 07:33 PM
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Default Re: How to test your A/C Heater Blower Motor and Resistor

Made this one a "sticky" to keep it on top

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Old 07-15-2013, 09:28 PM
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Default Re: How to test your A/C Heater Blower Motor and Resistor

Originally Posted by VALK View Post
Made this one a "sticky" to keep it on top
.... and I made it into a PDF for the list of problems and repairs in my signature.
PDF file.(click)

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