Hello all, I have a 2004 F350’. I am having a problem with the blower motor fan speeds. All controls (heat, A/C, defrost etc.) function as designed. the problem I have is the fan speed. The switch has four positions but only three speeds. It works on low, then position two and three blow more than low but the amount of air doesn’t change between two and three, then it works properly on hi. I replaced the resistor first, then the blower motor switch, then the blower motor. Replacing these parts has not changed the issue. I don’t know what else to look for. Any recommendations are greatly appreciated. thanks in advance. Joe.

 

and just how did you test the airflow ????

did you use an Anemometer ??

Verify that wires 2 and 4 on the blower resistor are actually switching to Ground when the switch is in ML and MH .. there isn't that much difference anyway.

BTW you should have 4 speeds .... when the Blower switch is in Low then Ground is supplied to Pin 3 of the Blower resistor to make the blower run in the low speed setting.

 

I will verify wires 2 and 4 tomorrow, my ,multimeters are at work. I did not test air flow, this problem just started two weeks ago. There was a noticeable difference between each position on the control switch, now there is no difference between M2 and M3. I replaced the resistor first because that seems to be the most common issue, when that didn’t work I kept replacing parts hoping I could solve the issue easily. I’m also going to verify the resistor is working the way it should even though its new. The issue still seems like it could be related to the resistor

 

it's a simple voltage divider

this is what I was looking at since you said the blower switch has 4 positions.....

 

Generally I just see the 3 position switch and it looks like this......

 

Thank you for the wire diagram, I understand how the resistor is supposed to work in conjunction with the control on the dash. The diagram is going to be very helpful in this diagnoses. I will post updates as available

 

Thank you to Lonewolf for providing the wire diagrams. I finally found some free time to solve this issue. I recently replaced the resistor and wire harness for the resistor. I purchased both items from our local NAPA. turns out the replacement plug for the resistor was wired incorrectly. the wires in position 1 and 2 on the plug were backwards. I reversed both wires and the blower now works correctly

 

good job

 

Do you happen to have the part number for that incorrectly wired plug?

 

Sorry, I didn’t save the packaging so I don’t know the part numbers but I know it was an Echlin part. When I cut the wires on the old plug, I didn’t pay attention to the position of the wires in the plug, I just made sure all of the colors matched the existing wire harness and connected them as such.

 

ECH-EC4 was the only one I had listed, but there is also a 5 pin ECH-EC75 <<== but I don't show that for the F series.


Easy enough for assembly line monkeys to flip a few connectors.. maybe they was Hung over that day

I would think they were machine assembled but easy to drop a few wrong color wires in the feed hoppers.

 

I've replaced burned and melted dash switches and their connectors, resistor networks and the resistor wiring harness---whether its the better quality of NAPA or even Ford/Motorcraft the wiring colors of replacement parts do not match with factory wiring colors. I've learned to cut each wire individually then match positions grafting the new parts in.

Just a bit of info that might be helpful.

 

Hey all, great info here. But I have a question about the replacement part being wired wrong, and also, if that is a common issue?

I have a 2000 F250 that had the usual resistor blowout where the speed only ran on high. Then it completely stopped working so I removed the old resistor and found the connector was melted to a crisp on what I'd say is pin 3. So I purchased a new harness/connector thing and a new resistor. I got them from Autozone. I noticed right away the colors didn't match the original connector so I wrote down a map with the factory colors/etc., and location on the connector. While splicing in new connector, I matched the wires on new connector, by location in the old connector. I didn't just go for color match as there is an orange wire in the new connector and the black wire is not in the same location.

Anywho, upon replacing and reinstalling, I have no fan speed at all, so I did not solve the problem. Taking readings with a multimeter(which I'll be 100% honest, electricity is not a strong suit for me), I'm getting power at the new connector for the resistor(also took the resistor out and check it and found no open circuits) but one of the speeds on the fan(I think it'd be M2 from what you all are saying), it's showing reverse polarity but is giving a reading.

Could that possibly be that the replacement connector was wired differently and I'd need to swap those two wires? I doubt it's that simple but figured I'd ask. I wouldn't think that would shut down the entire system but as mentioned, I am fairly clueless on this.

Side notes....

I swapped the relays and found no difference. Visually checked/replaced fuses to see if anything would change. The temp control **** and air flow direction **** still function(if I'm driving at a decent speed and put selector to defrost, I get a bit of air flow. If I switch it to say floorboards, I can feel air coming out there and nowhere else. Also, the temp coincides with where the temp **** is set at). I'm assuming the speed selector switch functions as the other 2 do and don't know how often 1 switch would fail. Also found a video that showed how to check voltage at the blower motor and regardless of speed setting, I was only getting between 3.5 to 4 volts at the blower motor. Maybe that helps pinpoint a faulty blower?

Anyways, thanks for any help/info. I'm new here and hopefully have figured out how to see posts/replies and such so I can keep in touch. lol.