Maybe someone can help me with a problem i have with my 95 f800 with a 5.9 cummings diesel. I am in need of a wireing diagram to try and track down a problem with my heater/ac blower motor. The ignition swithc has two terminals that show excessive heat and one lead one the harness. I have replaced the switch and replaced the terminal. When I check for voltage at the blower motor plug I get the same reading 10.8 with the heater control switch in the off position or on high. Does anyone have a diagram or a suggustion. Thank You in advance.

 

The blower is fed from fuse #7, 30 amp, from the fuse panel. This comes into the control panel in the dash on a brown/white wire. Any time your panel switch that says "off-maxac-normac-floor-mix-defrost" is not in the "off" position, this switch passes power to the fan motor directly on a orange wire.

The fan motor gets positive power all the time, except when the panel switch is "off". They control the speed of the motor by putting resistors in the negative side of the motor that goes to ground.

There is a orange/black wire that leaves the motor, and splits. One orange/black goes directly to the speed switch. When the speed switch is in "high", this orange black wire is directed straight to ground. This puts a full 12 volts across the fan motor.

The other orangeblack that leaves the fan motor goes over and feeds a resistor pack mounted in the ductwork of the heater. This is so air from the fan will cool the resistors. There are individual wires going from the resistors to the speed switch, and the speed switch selects which resistor grounds the motor, and this makes the fan run faster or slower. If your fan will work on high only, then I would suspect the resistor pack being bad.

The first thing I think I would do is find the orange black and ground it with a jumper wire to see if the fan will run. If it won't, then next thing I would do is run a scrap piece of wire from the battery + to the fan motor, and run the other terminal to ground, and see if the motor will work at all.

 

Franklin 2,

Thanks for your help and the fast reply. The motor works. I have taken and installed a inline fuse and toggle switch to run the fan motor that way. I want to return to normal operation. I am not sure what caused it to stop working, I suspect it was the ignition switch, I found two terminals on the switch that showed excessive heat and were loose. I changed the ignition switch, checked voltage at fan plug ( unpluged from motor ) and got 11 volts with selector switch in the off & hi position. I appreciate your help and if you have any more words of wisdom please pass along, I need all the help I can get.
Thanks again,

 

Check the motor voltage with the motor plugged in. This is a good rule of thumb when checking voltages on a vehicle. For instance if you are checking voltage at a taillight, make sure the taillight is plugged in the socket when you check the voltage. If you do not have a load on the circuit, the circuit voltage can "float up" and give a false reading.

 

Franklin,

Thanks for the help, I found the problem!! The function switch that has the vacuum ports on it was burned up. I have to order one from FoMoCo. I learned alot one this problem.
WOW, now if I can remember how to put the dash back together. Again Thanks alot for your help I really appreciate it.

Louie