crehder

I am replacing the heater box and 2 speed motor on a 1965 Mustang. The fan motor seems to work fine when jumping direct from the battery. Black wire to ground and either red or orange to positive and I get 2 obvious speeds. However, hook up the 2 wire firewall harness, ground the black wire, turn on ignition, and select either speed and I will get a spinning fan for less than a minute before the Accessory 14 Amp fuse blows. The 14Amp 'heater" fuse does not blow. What does the "heater" fuse do? Now I have not replaced the motor ($45)or the heater switch ($55). Is it possible the motor is pulling too many amps? Does the heater switch do more than control 2 speeds (some type capacitor, resisitor,...)? I can check continuity across the switch posts (3 legs) and I get good readings from the outside posts to the center post in each of the respective positions. I would appreciate any comments from anyone who has fuse blowing problems.

rtintwo

The possibilities are the motor, thermistor, switch or wiring. The fuse doesnt blow immediatly like will normally happen when a bare wire is shorted to ground so i doubt this is the problem. It is possible the the wires are corroded and have higher resitance creating a higher draw. The motor could have bad bearings or corroded brushes causing the motor to draw higher. The thermistor could have higher resistance than normal. The switch could be shorted.

I would start with unplugging the motor from the circuit and turn the switch on. If the fuse doesnt blow then its the motor if it does blow then its the thermistor or the wires(you have already checked the switch as good).

To me this sounds like a bad blower motor.

TexasAxMan

I'd suspect wiring. Was there other wiring issues with your car? The fact that it is not blowing the heater fuse tells me someone has tampered with the wiring under the dash.

That being said, try rtintwo's idea first, a lot easier than digging through the wiring ...

crehder

Thanks. What is the "thermistor"? I am trying to find a motor repair company to see how many amps the motor is pulling. Specs say 4-8 amps depending on which speed. I will try to post what I find out

crehder

In regard to the "other wiring problems" there were others but mostly just incorrect connections at the cluster and ungrounded runs. I am trying to figure out if the "heater" fuse only runs the fan motor. I am replacing the entire fan box and the new one does not have any kind of a "pre-heater" resistance strip that would require a fuse. I seem to remember seeing one on a similar car (Fairlane) but I can't be sure if it was this one. I don't see an unused lead for it under the dash.Of course, I am not sure what elements should be controlled by the Accessory fuse either.

rtintwo

The thermistor is the resistance elements that the switch runs the electricity through to change the motor speed. High speed goes straight to the motor the lower speed goes through resitors to slow the motor down. The thermistor is usually bolted to the side of the heater box, on the two speed 65s.

crehder

I didn't know about this. I will have to look at the heater box but I don't recall seeing anything bolted on there and I don't remember anything on the wiring diagram. I don't think I have any wires that would go to this location. Should there be a lead from the 2 speed switch on the dash plate to the heater box?

crehder

I'm back at work on the heater fan. Got the blowing fuse issue resolved and bought a new heater fan motor. Still have a concern. Even though the two speeds work fine, there is still a lot of heat on the fuse block "clip" when the fan motor has been running for 30 seconds. Won't blow the fuse but the fuse clip is very hot to touch. The wires leading to that fuse terminal, wires at the fan switch, and wires at the fan motor are not hot. I don't think fuses are supposed to get hot. Could this be bad fuse "clips"? I see fuse block rebuild kits with all new clips for $30. Not sure how to install them - some kind of rivet?