heater/defrost fan motor not working

[dougyounger]

The heater/defrost fan motor in my 77 is not working. I could use some troubleshooting suggestions to help me out.

The fan motor has only worked on the high speed setting for some time. Now high speed is no longer working. There is no sound out of the fan in either the low or high positions.

This is what I have done so far:

1. Visually inspected all of the fuses. Didn't see anything that looked like a problem. I could go back and test each to make sure.

2. Replaced the heater fan switch cable hoping there was a short in the switch. No effect.

3. Pulled the squirrel cage out to check for obstructions. Did not find any.

With the amount of rust on my Bronco, it would surprise me if I have a bad ground somewhere.

Any other thoughts?

Luckily, I've had a mild winter so far. But need to get this fixed before there is a significant weather event.

Thanks, Doug

 

[airbur]

Sounds like a bad motor if it went little by little. They are cheap.....do the upgrade.

 

[dube]

yes do the upgrade

 

[dougyounger]

I've had the upgrade on my bucket list of things to do but it has never been a priority. Now that it no longer works, it has moved up on the list.

I'll see if I can't find the parts and get'r done!

 

[Viperwolf1]

One speed working indicates a problem with the switch or a problem with the resistor behind the heater box. Since you replaced the switch I would say the problem is behind the heater box. Pull it all out and see whats wrong.

 

[dougyounger]

One speed working indicates a problem with the switch or a problem with the resistor behind the heater box. Since you replaced the switch I would say the problem is behind the heater box. Pull it all out and see whats wrong.

Where is the resistor behind the heater box?

What all is involved with pulling the heater box out?


From the upgrade threads, it looks like there are the two cables from the dash to the back of the box, four bolts that mount the box to the firewall, the wire for the blower fan and the connections for the heater core. Sound about right?

 

[Viperwolf1]

Need to unhook the defrost tubes, defrost cable, air flow cable, intake tube, heater hoses, and 4 nuts on firewall. Taking it out is easy part.

Do yourself a favor and replace the heater core seals while you're in there.

The resistor is screwed to the back of the box. The wires attach there.

 

[69red]

the heater box is fiberglass so if I recall correctly, there is a ground wire from the motor to the fire wall too. check and clean the contact while you have the box out.

I think its only 3 or 4 bolts holding it in -- pretty straight forward.

the resistor is on one of the wires going from the switch to the fan motor -- it gives you low speed by dropping the voltage.

edit. opps I forgot about the rest of the hook ups they can be a bit of a bear to hook back up

 

[dougyounger]

So if the resistor is bad, is just the resistor an available part?

 

[Viperwolf1]

So if the resistor is bad, is just the resistor an available part?

I've seen very similar new ones available. It might be. If not, should be easy to find used. Actually I'm thinking the wires may have just come off the spade terminals.

 

[work765]

can the resistor be accessed without dropping the whole unit?

last winter i went in and cleaned out everything and replaced the heater core and all the foam seals... and then summer hit and i didn't use my heater at all.

Fast forward to this week and it finally dawns on me that my heater is not working at all. I check the fuse and its blown. I then replace the fuse today and it still wont turn on..

where do i begin to find out the issue?

thanks!

 

[DirtDonk]

The good news (potentially) is that if the fuse was blown you likely don't have a failed resistor. At least I don't think it would do that.
Luckily if it is though, I believe the new resistors are finally available: http://www.wildhorses4x4.com/product/Heater-Blower-Motor-Resistor

But check all the other stuff anyway. If you have to, just pull the motor and see if it's free spinning or needs help to get started. If it's kind of frozen from lack of use, that could easily cause it not start and also to blow a fuse.

Paul

 

[jcasey12]

I would, and have, replaced the resistor in my 70 without going to all the work of taking the old (bad one) off. I just mounted the new one in a place that was accessible and pulled the old wires off and hooked them to the new resistor. Works fine.

 

[bronco t]

As Donk suggested the motor might be the culprit. I oiled the motor bearings on mine until I upgraded the motor and squirrel cage.

 

[Viperwolf1]

I would, and have, replaced the resistor in my 70 without going to all the work of taking the old (bad one) off. I just mounted the new one in a place that was accessible and pulled the old wires off and hooked them to the new resistor. Works fine.

A word of caution here. There's a reason why the resistor is mounted inside the heater box, it gets really hot, probably glows red.

All you have to do is loosen the box mounting nuts just enough to pull the box back a little to get on the resistor bolts. It's going to be tight but it can be done.

 

[work765]

Thanks guys!! I'll drop the motor tonight when I get home if I get some time. And see if it's free spinning!

I'll report back with my findings!

I swear, I drive my bronco daily. And i seriously have a new project or something to fix about twice a month.
But I will say, it's damn rewarding when you fix all those little problems. After a year I finally decided to fix my fuel gauge. So now I don't have to tap on the cluster to see the reading. And I have to say, Damn it feels good to see my true level of gas! it's the little things I life!


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[DirtDonk]

Hah! Very rewarding stuff!
Nothing like a working (or even semi-working) fuel gauge, eh?

Paul

 

[B RON CO]

Hi, yes, as mentioned be careful with the heater motor resistor. It is in the heater box air flow for cooling. They get very hot and can set leaves or paper on fire. Have you checked the wire at the heater motor for current with a test light? I would use my Power Probe to check for current, ground, and I can power up the blower motor to see if it works. Good luck

 

[work765]

So, I pulled the fan and spun it and turned it off and on. But still no sign of life.
So now I want to test weather or not it's the fan motor or some other connection that has gone bad.
What do you guys recommend? Should I get some long wires to go straight from battery to the on and off switch or to the back of the fuse box?

How would you guys proceed with the process of elimination?




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[DirtDonk]

Still the fan motor itself. It's still the easiest to test at this point, since it's out.
Run the jumper wire, or just put the fan motor up at the battery to save you the hassle, and see if directly connecting it to the battery does the trick. If not, then it's your motor.

If it does (and watch that it doesn't spin out of your hand), then yes, you can run a jumper wire to the switch.
But here again, it's easier to use a volt-meter (which every Bronco owner should have) or a test light to see where the power ends.

Oh, and do you check the fuse first each time, to make sure it's not blown again?

Paul