Help diagnosing why my heater blower motor wont turn on

[dzstang71]

Hello all,

I have a 71 coupe with A/C and I am currently trying to figure out why the blower motor is not turning on. It has worked in the past, then it the lower settings stopped working, then all together. The switch itself is a little hard to push up, but it gets there with a little force. I thought I would focus on the switch first as it is easier to get to than the actual fan motor and because of the stickiness of the lever.

I was inspired by this site, and with a great write up I found here, I tackled taking apart the center dash in the last couple of days.

There seems to be some discoloration on the top post of the switch and it was a little wiggly. Also on the plug it looks like some gunk on the corresponding opening. Maybe there was a short and that is melted plastic?

Also I found a plug on that same harness piece, back on bottom -drivers side, but I haven't a clue what it goes into. I thought this might have been a case of something becoming disconnected and tearing it apart would reveal the culprit, but no dice.

Any thoughts? Also is there a good way to check the switch and plug? I know to check ohms, but what two parts should I be having the leads on?

I missed checking the fuses, (that should have been first, but I was all fired up about taking things apart.) but I'll do that tomorrow.

Thanks!

-David

 

[midlife]

Yup, that pin that melted on the connector is the power pin. Now then, it is supposed to be fused, which makes me suspicious that someone has bypassed the fuse in the fuse box.

 

[72HCODE]

no those things always melt that is the main ground. mine melted also, the fuse is correct, i had to cut the wire out and clip the connector and make a new pigtale so i have to plug in the one wire separately to make it work, that stupid connector loves to work itself loose over time as well just from normal driving.

if removing and reconnecting the connector a few times to scrap some oxidiation off does not work or wiggling the connector doesn't show the problem then:

(sometimes those connectors get loose on the switch tabs and stop working, you can bend them a little with a screw driver and try to get them to sit tighter on the tabs)

If the fan works at faster speeds but not lower speeds, then check the resistor located on the side of the fan duct.

by the throttle pedal you will see the fan connector. pop that off and you will see a red piece of fiber plastic with the electrical tabs sticking out. there are 2 hex head screws.

remove them and pop out the resistor that is what controlls the fan speed, see if a coil has broken from rust or burnt out from heat.







if that looks ok and you test it with a continuity meter then i would suspect the switch itself that will require removing it and testing it on the bench or just flat out replace it.

if neither works then i would suspect a broken wire coming out of the switch connector going to the fan resistor pack.

 

[dzstang71]

Thanks guys! that gives me a lot more to go on with my testing. If thats the power connecter, I should be able to detect current there when the key is on, so that can hopefully rule out some of the problem to the plug.

Then I can test the switch and clean it up a bit. Thanks for the tip on bending it to fit better. I would like to put removing it lower down on the list, as the little knob seems like it's going to be a bear to get off, and might be destroyed in the process.

I will also find, then check out that resistor, it was working on higher speed, but now it's flat out not working, so I might have 2 different problems going on. Yay for multiple variables in the system!

David.

edit: upon further research, looks like the blower resistor is another part reproduced for mustangs other than ours. It looks like the scott drake repo for the 67-68. Anyone have experience on trying that out? for $18 it might be worth a gamble.

 

[72HCODE]

i would try messing with the connector on the switch, push it on the tabs as hard as you can with the fan switch on, and wiggle it around if the fan starts blowing then you found the problem.

sometimes my fuse box wiggles a fuse loose also,,, wouldn't hurt to pull the fuses in the box clean then a little and pop them back in and see if the fan is working again.

 

[dzstang71]

Hah! I got it figured out. It's the switch. The backing behind the top post is broken and it's crumbling apart. I was able to get 12v to the motor directly with a bypass wire and the motor works (yay). Still don't know about the resistor, but we will get to that when the switch is fixed.

Now to get that knob off. I think I have given up on trying to remove it while the it's still in the car, too easy to break something else or mar the faceplate while trying to get it off. My current plan is to use some cable cutters to snip off the switch arm and then try and pry off the knob with it in a vice. I was trying with a hack saw, but that is slow going, and I don't want to use my dremmel and have sparks flying around my interior. I might just have to order the replacement knob set in the long run though.

Anyone have tips on removing the knobs and keeping them intact?

 

[dzstang71]

Success is mine!

Nice to know all this burning of the switch is happening behind your dash.

 

[OLE PONY]

Great info in this thread! I'm rating it 5 stars!

 

[trainey]

If your fan works only on High, and Low, the resistor is bad.

 

[72HCODE]

yhea its great knowing there are 5 ways our cars can burst into flame without warning...

i had the same issue. i tried a couple ways i thought would solve it but nothing worked. i thought i had a bad connector or a bad fan pulling too much amp, but that isn't the case.

even after clipping the original wire installing a larger gauge, soldering the clip and cutting the burned remains from the original connector and making it a seperate piece the ground still gets hot when in use, hotter then it makes me comfortable with. i replaced the fan, and discovered the fan was fine it has to do more with the switch itself. the heat seems to come out the switch not the wire connection. I thought about maybe hacking in an aftermarket switch with a higher amp rating,,, but i just gave up and check that area from time to time.

 

[dzstang71]

I thought I would finish this thread off with a resolution.

I got the new switch from Old Air Products installed and everything put back together. The resistor turned out fine as I have multiple fan speeds.

Here is a picture of the new switch compared to the original.

Thanks for all the help and ideas.

 

[trainey]

Good to know about the switch, I know my resistor pack is bad. There was one on ebay once, and I missed it. If anyone has a working resistor pack, I'd buy it!

 

[Manu Mach1]

Good to know that the switch and only it can be replaced...

http://www.7173mustangs.com/thread-heater-switch--16984