2006 ford f350 heater fan only works on high or low nothing in between

You probably need a blower motor resistor , it work's through a relay for high speed an resistors lower the speed for low , medium etc... Videos on youtube on how to test ! How to Install Replace Heater AC Fan Speed Resistor 99 07 Ford F250 F350...

Do you hear the blower motor running ? Can you switch from low to high speed an hear the blower motor switch from low to high ?

Low pressure valve is located on top of the silver canister in front of the fan motor on the pass side of the truck

Need to change the switch that works high, medium, and low. It is a separate switch mounted usually behind the glove box or somewhere under the dash. Hope this helps, Mitchell.

I will assume the heater fan also doesn't work on low. You will need to replace the fan speed selector switch

I assume that you are talking about the heater fan?

Your heater FAN has at least 3 settings, and for our purposes we will assume low,med and high

Low and medium run through a resistor High is wired direct
Either your resistor is bad or your fan is
I know it seems wrong that the fan could be shot but it could be pulling so many amps that it won't work in any other mode than high
I just had this happen on one of my trucks
Start with the fan

sounds like the water pump is not performing correctly. some of the fins on the pump sometimes corrode and come off.

Change out the resistor for the fan motor it is next to the fan motor on a red plate in the air box

When your heater only works on high it is usually
the resistor unit in the heater passage housing. Look for wires ( about 4or 5 wires ) attached to the
plastic heater housing under the dash. It should
have a screw or two holding it to the housing. Pull
it out and you will see several wire coils. If they are melted or broken then thats the problem. On any switch position except high the power goes through these resistors to slow the fan down. Good luck. Neil W.

you need to check the battery's in all your key pads low voltage reception