I got a 1991 Jeep Cherokee Limited and here is my situation: My Aux Cooling Fan stopped working , PERIOD, doesn't work in any sitting. Also at the same time this happen, my Blower Motor Fan stopped working ( as I said they both stopped working at the SAME TIME ). I took the Jeep to a mech. that I know and trust and he replaced the Blower Motor. The Blower Motor is working fine at any speed- Low Med or High. The Blower works fine in Vent and in Heat setting. The problem is when I move the dial to Defrost, it blows the fuse to my Blower Motor. I and my mechanic know that when you need defrost, the A/C compressor kicks on and the Aux Cooling Fan turn on. Neither the ac compressor or the Aux Cooling Fan kick on. The mechanic says I need to take it to someone who knows alot more then he does when it comes to Jeep electrical problems ( he thinks its a grounding problem ). My mechanic did not charge me for the new Blower Motor, just the install. One note my air conditioning did also work before this, but now if I put in to AC Max , Norm, or Bi-Level, it blows the Blower Motor fuse. So at the moment I leave it on Vent or Heat, nothing else. Last I have hot wired the Aux Cooling directly to the battery with a switch. But of course I still have NO defrost. Can anyone help me?

 

Check the relay in the dash. Maybe the relay is bad. Check to see if the fuse is blowing because of a short coming from the engine or a short in the cabin. You need to use a multimeter for that.

 

Blower Resistors.
Do a quick search and Im sure youll find more info, maybe even a writeup.

 

you have a short to ground somewhere in your compressor wiring.

 

Im with you on this one
Check the condition of the cables on your fan and the compressor for worn out spots etc. if you can, Try to find where they ground and try to clean the contact areas.