I have been pulling my hair out trying to get my blower to run on all speeds. Right now it runs on high only. I pulled the resistor and replaced with 2 different used ones I got from a salvage yard and the same thing. It will even run on high with no resistor pluged in? Could it be all 3 are bad? 89 F 250 7.3

 

Usually the fan defaults to high if the resistor is bad.......I think you have a deeper problem. I will try to get a diagnosis in the AM at the shop.

 

Could be the switch in the cab that is bad. A bad switch, or bad resistor could each cause the problem described.

 

Just curious. You are installing the resistor in the air box when you try it?

 

Yes, I installed The used resistor in the box and there was no change. Then I unpluged the connector from the resistor and pluged it in the 2nd. used one in the open air and no change again. Like I mentioned before, the blower motor will still run on high even with no resistor.

 

the resistor is only used on 1-2-3 speeds ,4 high speed doesnt pass through the resistor
most likely the switch connector is melted and has no contact on the switch terminals
common problem on this model truck

 

I also picked up the switch and will try replacing that too.

 

Every blower resistor I have messed with (3) has also had a bad connector on the harness. Repair pigtails are available from Ford or aftermarket. The aftermarket pigtails may or may not be correctly color coded and you have to match pin location to the harness.

 

Butch may have the answer. Thats why many companies sell the connectors. I replaced the switch on the dash with no luck today.

 

Butch, yu da man. There was corrosion in the connector contacts. I went in with a Swiss file and cleaned them. Now all speeds are working fine.

 

Thinking outside the box, your problem could be with the blower motor itself.

I replaced my motor in my 93' after it stopped working entirely one day.

Curious as I am I took the old motor apart and could not believe what I saw. The brushes were completely gone and the thing stopped running after the spring holding the brushes had worn off.

I did not expect this at all. The contactor was worn away. It must have been some bad brushes, said it was made in Mexico.

Seb...