My heater fan only works on high intermitantly. It works fine, if turned off does not want to restart. Could this be a problem with the fan motor resistor ?
86 F150 351

 

Yes.

However when your blower is on high it bypasses the resistor.

You could have problems with both your blower and resistor and even fan switch.

1: Resistor bad so no low or medium speed.

2: Blower bad because of intermittent operation on high. Brushes in blower motor worn out and when it gets hot etc...

3: Fan Switch worn out.


There are some simple tests using a mutimeter or test light.

Brown/Orange wire is the main power feed to the blower motor from the fuse panel. Goes directly to the blower motor.

At the fan switch there are four colored wires.

Orange/Black is the wire from the blower motor and it for the blower for high.

Light Blue/Orange Hash wire comes from the resistor, and this is for medium.

Red/Orange hash also comes from the resistor and is for low.

Black is the switch ground.

At the switch connector

If you test the Light blue/Orange hash wire, with the ignition switch in run, If it has power, replace the fan speed switch, if it doesnt, replace the resistor.

As for the intermittent high speed blower problem. At the switch connector you can use a jumper wire to bypass the Fan switch. Jump the Black wire with the Orange/Black wire, if there is intermittent operation detected replace the blower motor. If not replace fan speed switch.

hope this helps.

 

Thanks ! I will give your suggestions a try. Will let you know what transpires.