• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Heater Blower Motor Stopped Working - Researched

Jonner

NAXJA Forum User
Location
Charlotte, NC
1998 XJ

Hey guys. I'm a long time lurker, finally doing some real troubleshooting instead of throwing parts at it (aka "rebuilding").

The blower has always only worked on 4 but recently started cutting out randomly 2 months ago. It would typically come back on after hitting a large bump on the highway. More recently it cut out again and when on 4, now sounded like it was on 1 accompanied by a low-pitched howling noise and a variable, very low speed.

I'm following the FSM starting at the blower motor relay. The relay passed all tests except it reads 68.8 ohms when the FSM calls for 75 +-5. This isn't too far off factory specs so I don't think this is the root of the problem.

The next step is to test the harness connector for the blower motor relay. The problem is I can't get the harness out without breaking it, to get good access to the terminals. I pulled the white plastic piece out of the middle of harness but can't get the harness to budge.

What am I missing here?
 
Last edited:
The first thing you are missing is letting us know what year model your Cherokee is.:twak::laugh3:

Don't worry about the relay, go directly to the fan motor and check if there is voltage across it when the switch is on. That gives you the most info in the shortest amount of time. My bet would be on a bad blower motor, especially because of the characteristic noise of shot bearings that you heard. They simply wear out over time. As they get older they draw more current, commonly causing the blower motor resistor to fail. The other common thing is the actual heater/AC switch, but check the motor first.

I preach troubleshooting first, but with the sounds, I would probably just replace the motor.
 
Wow.. that was fast. And check again, you may have missed the 1998 XJ posted at the top (don't pay any attention to the edited time at the bottom). :)

The blower motor resistor is the same one that controls all 4 speeds, correct? I replaced the resistor first, and then did some more research and learned that a bad blower motor can take out the resistor (sometimes twice if replaced) so I have been trying to avoid using the heater at all until I could get time to do some real troubleshooting.

I have a test light, FSM, and a multi-meter... let's see if I can figure this out.
 
It sounds like your blower motor is toast. I replaced the blower motor and resistor on a '93 that had the same symptoms. Your local autoparts store should have replacement for your XJ. More than likely you will need to reuse the plug from your factory blower motor.
 
So I managed to misplace the blower motor relay somewhere in the garage. I temporarily replaced it with a cooling fan relay. I haven't yet, but will probably test this relay to rule out one more variable.

I tested the female end of the blower motor harness across the 2 contacts for voltage and it's reading 0. I jumpered the blower motor directly from the battery and it runs ok. If the blower motor was drawing too much current, wouldn't it blow the 40A fuse?

I just checked the 40A fuse for the blower motor and it's good.

So I guess the next thing would be to test for continuity between the PDC and the blower motor? If that test fails, then start testing between the blower motor relay and PDC?

This is my first time trouble-shooting an electrical gremlin so any guidance is much appreciated.
 
You are making the job too difficult.

Inspect the dashboard switch and wires for signs of overheating/damage. Sniff for burnt smells. Repair/replace as needed. Check the wires for the Blower Motor Relay (BMR) relay for signs of overheating/damage. Sniff for burnt smells. Repair/replace as needed. If any of the 4 speeds of the fan do not work, replace the BMR. Test the current draw of the Blower on high. If excessive, replace the blower fan. If the fan motor howls, replace it. Adding an additional ground wire from the fan motor to the unibody sometimes helps.
 
You are making the job too difficult.

Inspect the dashboard switch and wires for signs of overheating/damage. Sniff for burnt smells. Repair/replace as needed. Check the wires for the Blower Motor Relay (BMR) relay for signs of overheating/damage. Sniff for burnt smells. Repair/replace as needed. If any of the 4 speeds of the fan do not work, replace the BMR. Test the current draw of the Blower on high. If excessive, replace the blower fan. If the fan motor howls, replace it. Adding an additional ground wire from the fan motor to the unibody sometimes helps.

The relay connections, switch connections, and blower motor connections all visually look good. There is no obvious signs of over-heating, corrosion, or chafing. The fan won't run in any position 1-4 in the on position so I can't test the current draw when the fan is running.

The blower motor sounds ok when I directly connect it to the battery. The problem is I can't get the blower motor to run any other way right now.

I guess I'll start working from the battery towards the blower motor testing connections. This is a daily driver and I'm lucky it's 45 degrees in Ohio this time of year. Thanks for the help but the only luck I'm having so far is with the weather. :(
 
Update...

I started doing continuity tests at various points between the PDC, relay, switches, and grounds. Everything was working properly. I was following some voltage tests in the FSM when I realized I needed to call it quits for the day. I wish I could share how I fixed it, but I can't. I had to button everything back up to drive to work, and lo and behold the blower motor works.

The only two things it really could have been were:
1) A broken relay, I may or may not have swapped it with the cooling fan relay as I was troubleshooting.
2) A loose connection. I loosened and tightend all the connections over the course of testing everything.

I'm thinking I should probably do the blower motor soon as preventative maintenance now that the jeep is at 188,000. I've read one too many sob stories about the BM issues. For any other newbs with similar problems, GET THE FACTORY SERVICE MANUAL and read through the intro on electrical and study the wiring for A/C - Heater diagram for LHD vehicles (if you're in the US and have A/C). Thanks a lot guys!
 
Last edited:
I've had switches burn up internally, still looking OK on the outside. Sounds like it's time for a trip to the junk yard. Typically, when a blower motor operates only on the highest speed, it means the resistors that slow it down are burnt or otherwise not working. Too much high speed means too much current flow through the switch, so I'm thinking the non-working resistors made you leave the switch on full, hastening its demise. I'm not familiar with second gen. heaters, but normally the resistor pack is accessible from the right footwell, and it's usually in the cool airflow, as they do get hot.
 
.... If any of the 4 speeds of the fan do not work, replace the BMR. ...

Sounds like a new Blower Motor Resistor will fix it.

The BMR gets hot and it gets wet/rusty. A new one takes about 10 minutes to install.
 
Back
Top