It happens at random times, with no obvious cause, I have changed the
resistor pack but to no avail. Is there a relay in this circuit?
My next option would seem to be to remove the dash to get to the fan
unit.

The fan is under the hood. You can check it's draw there.

There is a relay for the high speed.

Did you already smoke out the resistor pack? The switch contact is also
suspect for a melt and bad connection causing heat and caused by heat
that can melt fuses out.

I believe the rear window defroster is on the same fuse in our
Cherokee. That has caused strange fuse blows in ours.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

big AL wrote:

don't understand what you mean "smoke out", (I'm English), but I have
put in a new resistor pack, so I can rule that out. I bought a service
manual cd but have just found that although my Jeep was registered
1/1/1997, it is actually a 1996 model so the cd is useless, I need to
get the info for a 1996 model now.
:-(

When the heater switch or resistor pack blows from too much power draw
on a flaky connection, they can literally 'smoke out'. When the switch
went in our Cherokee, we were way out in the Canadian bush and it sure
let the smoke out. I was running for a fire extinguisher because it
looked like the whole dash might go up in flames.

It still didn't blow the 25A fuse.....

The resistor pack failure is an 'effect', not a cause of trouble
normally. Normally when the resistor pack fails, the heater motor is on
it's way out.

I would be suspecting your heater motor is drawing too much power. Does
it make any odd noises?

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

big AL wrote: