Hello all,
2004 e350 5.4 140,000 miles

Ive had this issue since i purchased the vehicle early this year. The front ac/heat fan only operates on high setting only.

Parts Ive changed starting with the most obvious:
*blower motor resistor (looked pretty corroded and the harness was seized).
*blower motor resistor harness
*fan switch

Possibly the blower motor itself can have these symptoms as well?

 

What's the voltage to the motor in other switch settings? Getting voltage is half an answer since the motor needs current to spin, but no voltage means the problem is upstream. I've I'd the situation in other cars where the motor would only start in max then could be turned down, suggesting worn brushes or bearings.

Sixto
93 E150 Chateau 5.8 191K miles

 

I checked the voltage to the blower. Im only showing voltage on high speed and nothing at all on all others which i suppose would indicate the problem to be elsewhere. I checked all fuses and relays and everything seems to be fine. This is a long shot and most likely not related but i did notice 3 wires to the right of the intake that go to nothing and look to have been removed from the wire loom. Also, isn't that main wire harness supposed to be protected instead of exposed like that? Cant remember how it was on my other e series.

 

Finally Solved!!!
The new resistor was defective (see pics below). The main power post was broken at the weld or crimp. It was only by accident that i figured it out because when i put my multimeter on the post, i gently pressed down and the circuit completed and the fan turned on. Thats when i noticed the break in the post. Otherwise i would still be searching or would have given up. Wound up pulling the dash apart changed the switch tracing wires, pulling relays, fuses etc.. Thanks advance auto.. 6 hours total to change a blower resistor!!
Yes there were other things I could have checked first to verify the faulty resistor but there was also a learning curve for me on how the system works. Very simple now that i think about it.

 

Congrats! That kind of stuff really pisses me off. I was thinking the loose wires you spotted were going to be at fault. You're not alone though. A few weeks ago I replaced a wiper motor with an aftermarket. This past week I had reports of the wipers only working intermittently. I investigated and concluded that because the old motor had gotten very hot it must have compromised the harness side connector - jiggle the connector, and the wipers came back on. Couldn't be the motor since I just replaced that, right? So after installing a new connector with nice soldered splices and heat shrink on each of about 12 connections.... same problem. I hate to get another one of these junk motors, but of course this is a warranty issue. Should have gone with the Motorcraft part... lesson learned.

 

FWIW those blunt-cut wires with shrink wrap on the ends aren't mistakes or hack jobs---they're part of the wiring harness that is left unconnected as that particular chassis didn't need the signals they transmit.

One is for Clean Tach Out, another for 4WD engagement, forget what the third does. They're not at all associated with the HVAC system.

Oddly enough most don't know they're left loose but part of nearly every wiring harness since '97 or so. I had to dig for mine some time ago---more curious than anything at the time.

 

I think i was getting pretty desperate at that point lol. Glad to know those wires are there for a reason other than being cut. Thank you for the explanation