Blower Motor Fuse Keeps Popping

91' Laredo 4.0, np231, aw4, its a heap.
Replace the fuse, and the blower fan will work for for a minute or so, then it will blow again. I ran the fan directly off the battery through a 25 amp fuse and it did not blow that fuse so I'm pretty sure the motor works correctly. I have all speeds before the fuse blows as well so pretty sure the resistor is still working. Really think it has a short somewhere and looking for advice on how to track it down. The wiring diagram in my FSM doesn't show the fuse or relay so it isn't very helpful. And recommendations are appreciated, Thanks!

If you had a short; even the 25A fuse would blow.
Have you checked to see if the fan motor is spinning freely?
As a motor runs the windings will start to heat up if the motor does not spinning freely.
Consider removing the fan motor and blowing out any debris or carbon buildup. Put a small squirt of WD40 at either end of the fan motor shaft and test to see if it spins freely.
If you have a good multi meter you can select DCA and connect the leads between the motor and power lead to see how many amps are drawn during spin up and operation before and after the cleaning....

Here is the book of what I have checked so far:
When it first quit working I checked the fuse to see it was bad then replaced it. The blower still didn't turn on so I checked the relay and it had clearly been heat damaged. I then replaced the relay and the motor. The old motor was hard to turn and really dirty. After replacing the fuse, relay and motor, I tested it out and it worked fine. I thought I was done until the next time I got in the Jeep it blew the fuse. I then wired the motor up directly to the battery through a spare fuse holder and 25 amp fuse I had to make sure the motor wasn't drawing too much current. It worked fine and never blew the fuse when wired directly to the battery. I'm pretty sure there is a short somewhere, but the wiring diagram in the FSM doesn't include the fuse and relay so I'm not sure where all the wires that could be shorted even are. I took all the ancient tape and plastic surrounding the wires from the fan to where the wires go into the fuse block on the driver side of the firewall in the engine compartment. All the wires here looked fine. I think the most likely location is in the dash but I have never taken it apart and I still don't know how the relay in the power distribution block in the engine compartment factor into the wiring.

When the fan is running do you feel air movement thru the climate control vents?
If the dampers are closed inside the ducting; due to being dead headed the motor windings could heat up causing the fuse to blow.
The ventilation dampers are vacuum actuated and the loss of vacuum to them could cause this problem or the linkage could be bound up.

For the minute or so that the blower fan worked before the fuse blew, it seemed to be working perfectly. I could cycle through all the blower speeds and the vents worked properly. When set on 'vent' it blew like normal through the vents on the dash, like on each side and right below the climate controls where it is supposed to blow out. I was moving when the fuse blew so I could have hit a bump that caused a frayed wire to touch metal or something. That's why I was looking for some help figuring out where all the possible offending wires run.

Update for the sake of completeness. Orielley's sold me the wrong relay for the blower motor. I looked at it at the store and thought it was the same but it wasn't the coil on the diagram was on the other side than the original relay and I didn't notice. I went back to Orielley's and picked up a relay that had the exact diagram, except mirrored but all the terminals matched up and the coil was on the proper side. Apparently all that matters and I wasn't familiar enough with relay schematics to know. Anyway, everything works now that I got the right relay installed so there must not have been a short anywhere.

Thanks for updating with your solution -- wish everyone would do that.

I do wish that we could see the diagram as I'm not sure what you mean by the coil being on the wrong side. It would be helpful if you have the part numbers for the two relays handy and could post them.

No problem. Usually the only time I don't post a solution is when I don't find one. I'll try to post a pic later tonight that shows both relays and comment what I mean. I don't have the receipts though to remember the part numbers :dunce:.

what he is trying to say is he either got a normally open relay and put it where a normally closed relay belongs, or vice versa.

Glad you got it worked out, electrical issues can be some of the most frustrating.

Sorry for the huge pic, I don't feel like resizing it again and you can see better this way. Anyway, the relay on the left is the replacement relay that DID work. The relay on the right did not work and blew the fuse. The only difference I can see is that the coil, or the little box figure, is on the 87 terminal side on the working relay whereas the coil is on the non-working relay is on the 87a side. I guess there is some relay convention or SAE code that I don' know about that dictates the terminal closest to the coil means that terminal is normally closed or something but I don't exactly know. I thought the position of the switch meant something in regards to being the NC or NO terminal but I was apparently mistaken. I couldn't find the original relay, maybe I threw it away, but its diagram was a mirror image of the working replacement relay. Feel free to chime in with your own relay expertise or relevant links.