ford truck blower fan only works on high

[Bob]

I have an 2004 f-350 and the fan only works on high. i ve changed the resistor and pigtail. switch and fan motor with no luck. any advice?

[Karl]

Well, it would not have been a bad motor, since it works on high.
The only thing that controls blower speeds is the resistor, except for high. That is its own 12 volt feed.
If the resistor did not fix it, then check all the fuses. There will be one for high, which we know is good, and one for the other speeds.

[Bob]

checked all the fuses and they are good?

[Karl]

OK. Then you are going to have to check for proper voltage to the the resistor block. The voltage in will change to a different wire when the fan switch is put in different positions. If not, then you have a wiring problem between the fan speed switch you replaced and the resisitor.

[Bob]

i dont have any power coming out of the fan motor. orange and black wire. power goes in obviously but not out. noticed that the ground strap from the block to the firewall is broken. could this be my problem?

[Karl]

Well, you wont have any power coming out of the motor. That is the ground side. To test a ground, connect your test light to a power source, then touch the other end to the disonnected ground wire. The light should come on if that wire has a good ground.
Do you have power going into the fan motor on all speed adustments?
I would fix that ground strap to see if it help.

[Bob]

fixed the ground strap still no luck.

[Karl]

Do you have power into the blower motor or resistor on all speed settings?

[Bob]

yes, power into motor and resistor on all speeds.

[Karl]

Well that does not make sense that you have power into motor on all speeds, but only high works. I think you are going to have to find a wiring diagram and check the ground circuit for the resistor. Again, high speed does not go through the resistor.

[carriedi]

the brn/orange wire should have power from the blower relay. through fuse 107 = 40a. the orange/blk wire grounds through the blower controls. High by passes the resistor. Going into the resistor is LOW grn/white, MED is yellow/red. ground is the blk wire. orange/black if fan mtr.
fan on high - blk/orange will be direct ground.
fan on medium - yellow and red will be the ground
fan on low - grn/white will be the ground.

turn heater switch to heat with the key on.
with the blower motor switch in the low position touch a fused jumper from ground to the grn/white wire at the resistor. does the fan go on low? if the fan goes on low the resistor and relay are working. you need to look at the control head. If it doesn't the resistor may be bad. they have a thermal protector like a fuse. if it gets hot it blows and it's finished. That's why they put them inside the heater box. so the blower will blow on them and keep them cool.