I have a 74 F100 with AC. A few months back my Heater/AC control broke which was fine because it was on the "On" position. A couple of days ago my blower stopped working. Thinking it had to do more with the already broken controls the junk yard search was on. After numerous phone calls and many driven miles through the town yesterday I found a heater/AC control for a 75 f250 that fit perfectly (except for the switch for the dual tanks which I had to use my own due to the harness the new one used was different). I hooked up the new control which made all the things work like they should again but the blower still would not work. I finally found a tiny fuse box, by itself on a wire, aftermarket apparently cause it used the newer style square fuse instead of the round ones, with a blown 30 Amp fuse. Replaced the fuse, and the blower worked. Thought I was done for the night and went to bed. Today, in the 115 degree AZ heat, I find that the fuse was blown again after about 3 minutes. Replaced fuse and it lasted for about 1 minute.

What is going on? Why does it keep blowing my fuses. Now, I can only assume it was blown before I switched out my control box cause it didn't come on after I started it up when I replaced it.

Now there is also a second question. The blower motor contol on the 75 box had four wires as does the 74. But the wires are of different colors. According to my Hanes manual, they should be the same, hence the reason I didnt mark them when I removed them from my 74. Now following the wires back I was only able to see where one went and looking at the 75 box I know that one wire is correct. In the few precious seconds that I do get of AC after I change the fuse the blower motor does seem to be working properly, ie. it blows low and fast when I move the switch.

Why does my motor keep blowing the fuse. It appears to be working when the fuse is good. Why is it getting enough juice to blow the fuse.

Any help appreciated since my ex-wife comes back from vacation in less than a week and I'll have to give her car back to her. It's 7:12 PM right now. It's 111 degrees outside. You can understand my urgency! Thanks!

 

Offhand I'd say the motor is seizing up.

Too much draw on a motor that won't spin easily,thus Blown fuse.

 

should have asked this question earlier too. Where do I find the blower motor. Not too familiar with the insides of the AC box.