2002 Jeep Grand Cherokee Outlander
Any help? I had recently replaced the blend doors by cutting under the glove box. After doing so the blower fan would not shut off, even with keys out of ignition. I replaced the blower resistor, and with the new resistor I can't get any function out of the fan whatsoever. If I hook up the old resistor, the fan blows one speed, and still won't shut off. So new resistor=no function, old= one speed/won't shut off. I disconnected the climate control on the dash, and the fan still runs

 

The fan motor is wired hot and the heater controls and resistor are the ground circuit. It sounds to me like the wire from the fan motor to the resistor is shorted to ground somewhere. Does the resistor connector look like it's melted at all?

Also, it makes a difference if it's the automatic climate control unit or the manual one. The automatic unit uses a control module instead of a resistor. Make sure you're using the right one.

 

Ok I was just thinking myself it may be the harness connecting the resistor to the blower fan. Or module I guess, it does have automatic climate. I matched up the part before installing. Connector did not seem to be burned or melted.. but that doesn't mean it's not shorting out still. Will try to get wiring harness tomorrow and see if that does it. Can I test that connection with a multimeter? If so, how?

 

It sounds like you may be onto something with looking into the blower motor control module. You have the automatic zone control AZC system. There is no resistor. There is a blower motor controller in its place instead. The controller allows near infinite adjustability of the fan speeds. The fan speed can be controlled manually by the fan speed control **** on the panel.. Or, the speed may be controlled automatically by the control module. In either case, the control module is what provides modulated pulses to the controller for the blower motor ground circuit.

If it was not equipped with AZC, it would have a resistor instead of the controller, and no control module. Instead, the resistor would be providing resistance to ground via resistor wires. On the lowest fan speed setting the resistance goes through all of the resistor wires. On the highest fan speed setting the resistor is essentially bypassed. The blower motor basically recieves power and ground direct from the battery on the high setting. This is why the blower motor is still able to run even though the key is in the off position, and none of the accessories are even supposed to be energized (outside of maybe the lights).

To test the module you may need a scanner?

 

I found this online too:

(copied and pasted)
Problems with a blower motor control module are less frequent, but it fails for the same reason: due to corrosion or overheating when the motor is jammed or shorted. In most cases when a blower control module fails, the blower motor doesn't work at all. In some cars (e.g. older GM trucks), a failed blower control module or processor can cause the blower motor to continue running even with the ignition OFF.
(end copy & paste)

I don't know that you can check the control module or not with a DVOM? I would think so, but what I read says it requires a scanner for a proper diagnosis? I don't know why?

You can definitely check a resistor with a DVOM for Ohms to indicate a fault, but that is not what this is? The Ohmmeter may show an open circuit when it happens in a resistor as O.L displayed when checking it.. Which makes sense, since the power is always going through here. It is the ground supply that is being resisted, or opened. The faulty parts circuitry may be stuck open? That is how it would remain on like that, right? Something could cause it to ground out? Although, I don't think electricity always follows the rules, or does what you would expect it to do in every case?

 

The AZC system is self diagnostic and you can get trouble codes from it, but alas, I do not know the procedures of how to get them. It is spelled out in the FSM and is quite complicated and I never needed to know it.

Usually the reason for the modules failure has to do with the blower motor drawing too many amps from worn or binding bearings. This is the main reason for the resistor to melt in the manual control system also.

 

That's right. I recognize it as being a likely reason for the blower motor control module failure too, is too much amp draw by the blower motor. It is probably good to make sure for trying to prevent it from happening again in the future?

The blower motor can definitely be verified and tested with a multimeter to see if is drawing too many amps, or not? So that it does not overheat the control module (or the resistor).

If you had ultrasonic testing applications? You could see the sound waves of a blower motor asset pulling too much of a load, drawing too many amps that way too.

 

All fixed!! Thanks everyone for the help. Was a stupid issue. While pulling the old control module, I must've grabbed one of the wires on the connector to the climate control. While messing around today I noticed one of the leads was exposed a little. Pushed the wire back in, and viola!!! New module works like a charm!

 

And for AZC self diagnosis... hold a/c and recirc buttons, and simultaneously turn driver side temperature control clockwise one click! The self diagnosis did not help me with this problem however!