Recently my '90 Trooper decided to leave the heat/blower on all the time. Even when the AC switch is off and fan speed set to lowest, it is always on. I can however switch the fan speed switch and it speeds up, seems like it is stuck on the slowest setting.

Checked the fuse in the fuse box, it's good. Anything else? I found some old posts about peoples blowers not turning on, but my problem is it wont turn on. Thoughts?

Replaced the relay under the dash with a brand new one, same thing. The relay by the driver side headlight was nasty! I cleaned it really good, plugged back in and same thing.

No one has any thoughts?

I had trouble getting the high to work on mine, I was like only getting like 11 volts on high. Someone was in there cutting and splicing and rewiring ,It was a mess under there. I spent 10 or 12 hours and never could find the problem, so I just put a toggle switch on the dash and ran a wire directly to the fan from a circuit that's shuts off with the ignition, problem solved, I never used anything but high anyway. And now it's easier to go from off to high, I don't have to go through low and medium. You could do the same thing but put the switch between the fan and the factory switch and use it to completely shut it off.

I had a day when my blower wouldn't shut off, even when the key was out. Everything else seemed fine, but the alternator died completely right after. I'd check whether your alternator is charging properly and maybe check the blue relay in the fuse box.