Unless the HO Jeeps have a different resistor pack than Renix jeeps (which I doubt) many posters here are confusing a resistor with a thermal fuse that physically looks like a diode that is part of the resistor pack, but it is not a resistor. The actual resistors are massive coiled wires, and they only go bad bad after very long exposure to water (condensate from the AC) and corrosives like maybe road salt up north (which I have heard rumors is taking its toll on later model HO jeep evaporators, and maybe the resistor connections as well, they are crimped,....and other vehicles of the same vintage that have aluminum evaporators, or leaks from an evaporator or heater core that leave corrosive salts behind on the resistor wires. Those resistor wires get red hot, and any organics that get on the resistor (like antifreeze, or refrigerants and oil) will decompose the organics forming organic acids!!!!!
That thermal fuse would fail from a locked up motor (I think) or from a blocked air flow (like an iced up condenser?) as the resistor wire would not have air passing over the wire to cool it and the thermal fuse would sense the dangerous temperatures and blow the thermal fuse.
X2 on Old mans post!
Also, you have no idea how old the blower motor is on a newly acquired, used jeep. It might be new already!!! So look at the history, and age of parts, actually pull the resistor pack (takes about 2 minutes), and the fan switch, takes 5-10 minutes, and look for loose burned, corroded signs of the problem.
Lastly, on the Renix jeeps (Did the OP ever tell what year his beast was????), the wire that goes from the fuse box, to the ignition switch to the fan switch and the resistor pack and motor, is way overloaded with other accessories on it like the radio, the WSWipers, the electric door locks and electric windows etc, and the failure problem is frequently compounded with poor, old dirty previously overheated contacts at the fuse box and the ignition switch. I had to bypass both fuse box and ignition switch and run new wire and new fuse holder on my 87 and 85. That was over 5 years ago now.