Problems w/ my 1999 Tracker

I am having problem with my trackers 15 amp heater fuse blowing. i have replaced the fan motor, fan relay. I have also tried unplugging the air conditioner and that seemed to work for a couple of weeks. Does anyone have any suggestions as to what I should try next?

Does it blow on low speeds or just high or both?
I would check the amp draw on heater blower motor.
Also check resistor block and wiring for short.
MT

Not that it's always a safe fix, but mine blew for no apparent reason 3 or 4 times last year. I finally ran out of 15 amp, so I replaced it with a 25 amp and it has worked fine since. This has been at leat a year and 30,000 miles ago, if something was going to burn up, it probably would have by now.