I have a 92 XJ. The blower motor has been making noise for a while now and finally quit working. So I figured it was the blower motor so I picked up a new one. Well, it didn't fix it. The wiring at the plug at the HVAC panel was melted so I picked up a new plug, new blower switch, and I threw a new resistor in for good measure. Blower still does not work. I said alright, maybe a bad blower outta the box so instead of testing it, I just swapped it out at Advance. Put it in, still nothing. So I tested the blower, it works just fine direct to battery.

Here's what gets me. I have 12v hot and ground at the blower motor plug on the harness. As soon as I plug the blower motor in, the voltage drops off to nothing.

HELP, winter is coming.

 

How do you know the voltage drops off when you plug the blower motor in?


What plug on the HVAC panel had melted wiring? The bower speed switch?


There have been cases where the power-in slip ring inside of the climate control panel selector switch has arced out. This could be your case. Not saying it IS your problem but an arced slip ring could be causing enough resistance that when a load is applied (blower) there's too much of a voltage drop across the arced slip ring to operate the blower.


If you remove the connector from the blower speed switch and, using a test light, probe the connector pin cavity with the wire going to the selector switch (+12 Volts) and see if the test lamp glows dimly or is bright. If it's dim then I would suspect the selector switch or a bad butt splice on the new blower speed switch connector. If the test light is bright, the problem is downstream of the blower speed switch.


The selector switch is held on by two screws. It's a matter of removing the vacuum connector, the electrical connector and the two screws to remove the switch.

 

I know it drops off because I'm checking the voltage at the plug for the blower motor with a multimeter. Unplugged, the plug has 12v constant and ground. I plug the blower in then the plug has no power.

The blower motor switch plug is what was melted. I replaced the plug and the switch. I have voltage at all different pins on the blower resistor so I'm going to assume the switch is working fine.

 

how much voltage. the sw and resistors pull the motor to ground i think. if you have 12 v you have no ground on the sw. ill get a look at wiring asap.
my xj 2000 wiring shows 12v going thru motor to resistors and sw to ground. motor must be ok. the sw may not be making contact to ground. volts on res should be low to zero at full speed.

you should be able to ground the resistors and run the fan as a test

my 2000 may not match yours . how many ways can they do it?!!

 

This thread has some great info... I will be watching because I have an issue where the blower motor looses power as I press further down on the accelerator. Electrical issues always throw me off to begin with and have NO idea why this would happen... I'm wondering if it's similar to the issue you have...

 

NED STARK!

 

It has no resistance to ground. I even grounded the motor directly just in case and no difference.

 

then its on the volt supply side, high resistance as was mentioned b4. strange problem.
when you ground motor what voltage is on the supply side conn or sw?
i dont have wiring for yours .

 

Grounding motor does nothing, the voltage stays at 0 volts the same as being ungrounded direct to battery. I don't think I mentioned high resistance. 

 

Grounding motor makes no difference. I do not have high resistance.

 

if you ground one side and the other side has no 12 volts, something is open on the 12 v side!or the motor is open which you say is good. open = high resistance.
12v on one side,ground on the other,it has to run!!
open 12v, or open ground. there aint nothing else left!

picture the motor like a light bulb, it must light!

 

Yes I've tried two different motors which both work hooked direct to battery. It must be something open on the supply side since it keeps losing 12v once you plug motor in.

 

you need to put a jumper wire around those items in series with the 12v to the motor. i dont have your wiring info.

resistance somewhere was mentioned b4.

when you find it it will be something simple!!

 

So you want me to have then blower plugged in, then jumper the two blower wires together as well?

I tested it with the blower plugged in then ran a jumper from 12v constant to the blower and it kicked on.

 

Defective connector/ wiring @ the blower motor.