having trouble with my heater motor in my f350. it runs wide open and cuts completely off when I turn the fan down....is the relay bad?...

 

Welcome to the site..

If a manual climate control,, the Blower motor resistor.. The resistors thermal 'limiter' burns out and the only fan speed that will work is HI fan.. If a ETC (electronic temp control) the blower motor spped control unit.. Depending on which option, they both mount in the same place.. Under the hood,, look at the passenger side up close to the firewall and you'll see the blower motor.. Over to the right you'll see a '2' screw unit with the harness/connector..

 

thanks for the tip i will check it out on my day off..

 

If you have standard climate control (?) the resistor thermal limiter looks like a diode stretched across the heat piles.. When it burns it goes 'open' internally.. Let the resistor hang while connected, and as a 'test' take a test lead/jumper and cross the 2 connection points of the limter.. All the blower speeds should work..

 

do you park it under trees? If so you can get leaves into your blower motor and i can cause the door not to close all the way or at all.

 

thanks for the help. it was the module for the heater motor......