Two weeks ago, I replaced the heater core on my 76 because the radiator was feeding a leaking heater core and my carpet was trying to absorb it. Not a hard job, just tedious. Anyway, today it was 31 outside and I needed the blower to work, nope! I cleaned the ice off the windshield and drove to work. About an hour age I replaced the fuse, turned on the blower, it ran for about 3 seconds and again, it blew. Should I have replaced the blower motor, too? I realize there a short, where should I start looking for it? Any help will be appreciated. I do not like playing with electrical things. Thanks, Ken
First of all did you by any chance check to see if the blower motor moves freely? If it's binding after it gets warmed up that could cause it to blow the fuse after running for a bit, I would also check voltage at the motor and check for continuity along the power feed wire and maybe make sure the ground wire is getting a good connection. 12 volt DC stuff won't bite ya like the AC current will, when I need a pick-me-up I just hook up the battery charger to.....uuhhh ooops never mind.
Well, the blower worked for the short time, (20 minutes), I needed it before. Thanks for the help, Saturday should prove to be fun! Ken
When I was having a similar problem (though my fuse blew as soon as you flipped the switch) the problem was a seized motor shaft. I replaced the motor (which is easy--except for the removing the dash part LOL) and voila, a working blower. There is another component that could be faulty but I'm not sure if it being faulty could actually cause the fuse to blow. There is a resistor on the base of the heater box--it's a thick red circuit-board-looking thing that the wire to the dash switch goes to. The idea is that it lowers the amount of power going to the motor to vary the motor speed. I could see it being faulty and causing too much resistance. When I inspected mine the wire connecting to it actually had the plastic clip melted. The resistor is the easiest thing to get to and the easiest to replace, assuming you can get a replacement part for it. If you know how to work a multimeter, testing it should be simple and something you can do without taking anything apart. Since it's easy, that'd be my first step before tearing open the dash.
I do remember seeing the resister plate on the housing. If that is bad, what are my options? Thanks for your response, Ken
If the resistor is bad you'd just replace the whole plate. They're on eBay every so often but I don't have the parts reference right in front of me. I won't be able to look it up for a few days at least. Sorry I can't be of more help.
The resistor ( for the lower fan speeds ) is out of the circuit when the fan is on high. The bad thing with the resistor is that it relies on the air from the fan to cool it. If the motor is stiff or frozen and the fan is on any speed but high and not enough air flows to cool the resistor. It can ( and will ) melt, possibly catching leaves or debris in the heater housing on fire! I've had this happen in Ford products over the years, as Ford didn't feel it necessary to put a screen on the cowl vent. Since you've had all that apart, I'm sure you cleaned out all the crap in it. The other problem I will mention is that if you have a sluggish motor when you use high fan the fuse will probably blow. If you have other speeds selected the current is reduced by the resistor and the fuse may not blow! I'm not trying to sound doomsdayish here, I just want to convey that a free spinning motor is an important thing! Mine ( that also worked fine before ) is starting to screech after running a few minutes. Since I also need a new heater core, I'm going to get both parts before attempting to pull my heater box. Mine has factory ac so I'm not really looking forward to this job! Ford must have had heater core problems in the 70's, cause almost every one I see has the heater hoses plugged!
Simple man, yep, I wish I had changed the motor at the same time as I changed the heater core. If I were you I'd add an A/C evaporator core while I have it apart. You'll need to take it and clear out the Freon anyway. You'll love all those vacuum lines too. Ken
I think you just explained what caused a Ford van to catch fire in the heater area a few years ago. The burned up heater box, blower, and wires were replaced but we never understood what caused it to catch fire. It had a wheel chair lift and was being donated to an elderly couple that desparately needed it and had no other means of getting one. Sure hated to see that van go out with an undiagnosed fire to transport a woman in a wheel chair but out it went. We would have breathed easier if we had that explanation back then.
I got some model paints just to mark all the hoses to where they go. I'll change the evaporator just to be safe, even though the air works fine now. I definitely don't want to have to do this twice! I've seen several cases of this! I'm in the habit of putting my fan on high first then put it down to the speed I want. That way I know it's running. I always turn the fan off also. I noticed in the vehicles that had fires in the heater ( all Ford products ) that the fan had been left on with a lower speed selected. I will only guess that when the vehicle was started, the fan didn't run and the resistor set debris in the heater on fire! I actually tried this with a fan motor and resistor I got from the junkyard. I connected them as they would be in the car and held the motor from turning. In 8secs one of the coils on the resistor was red hot!!! Each speed turned a different coil hot. I don't think this would cause a fire unless the heater box had leaves or pine straw in it, though. Then again, when have you ever seen one of our cars without a bunch of trash in the heater box?
Glad you found it! That motor uses a lot of current when it's on high! I've found that the ignition switch will fry by being lazy and just leaving the ac turned on when you shut the car off! My ex was good for that! Just turn the key off and leave everything on!
