108 blower motor problem
 

I have just finished replacing the heater control levers on my 108 280 SEL 4.5 sedan (1972) and the heater blower motor works intermittently. I do not know if this is a preexisting problem as the levers have been frozen since I got the car. I can remove the back of the plug and jump the wires and get it to work and I have also gotten it to work with the new blower switch once. Any clues or suggestions. I do not want to re-install the levers until I correct the problem for obvious reasons.

Hoo Boy...

Try this;
Pull the cowl off so you can stick your hand in there and clean out the inevitable leaf, or other stuff. Give it a spin with your hand, and you should be good to go!

Yes, the cowl is just behind the hood, in front of the windshield.
Yes, OUTSIDE the car.

OK. Pulled cowl off, filters still in place prior to pulling off, reached in and found no debris, squirrel cage spinning freely. Fuse good. Now more to add.

With plug attached to switch and using light probe have discovered the following..... With switch off I have power to one wire. With switch in any position I have power at all leads no matter what speed position I have blower switch set at.

I tested with switch plugged in and back of plug removed. I am definitely not an electricial genius and am still stumped. Where to next?

You need to find the resistor (for low speed, there are only two) and check it out. You should have a ground through the switch if you have power on the blower.

What is happening is that power is applied to the blower all the time, and the ground, either with resistor (low speed) or without (high speed) is through the switch.

If the ground on the switch is bad (wiring harness with broken wire, etc), no blower. It runs when the ground is good, won't when it is bad.

Check the continuity of the switch on the levers. If the switch is good, you can install the levers without worry, they are not the problem. If not, you need to repair it -- slide contacts on the air control lever. Lever must be in the far left position for high speed to work.

Peter

When you say "find the resistor" , do you mean physically locate the resistor or find the "resistor" in the line somewhere, meaning a short or something like that. I will check the switch again to make sure but at last test it was good.

As I said in my first post I have been able to make the switch work by jumping the wire from the power lead to individual poles but even that was not everytime. Does the bracket itself need to be grounded or is the ground in the wiring that attaches to the switch?

I apologize if this may be Electrical 101 but I really do not know much about it.

Jeff:

I will dig up the wiring diagram and see what it supposed to be where tonight.

I think you have a bad connection somewhere rather than a bad blower.

Peter

Well, if I hear this right then, Peter, The switch must be touching some metal on the dashboard in order to complete the ground.

So if the switch and levers are disconected from the dash and are waving around-attached only by the cables, there wouldn't be a ground, ergo no fan operation...

Jeff;
Whilst you have the cowl off, squirt some liquid grease into the bearings of the motor.
I used a piece of tubing intended for the repair of window screens, you know the little round rubber "rope" you push into the screens sides to keep it together...? Makes a good fit onto the squirt tube which comes with the liquid grease.

Ed

Thanks for taking the time to look up the diagram Peter. I have already greased the motor but thanks for the tip. My original thought was that I had a bad ground and I "dry" mounted the levers in the dash and hand tightened the nuts. Then I checked the operation and still no go. I even grounded the bracket while I had it out and tested to no avail. When it worked those couple of times it was not grounded to anything then but I did it just to make sure.

So, other than the fuse, there is no resistors in line or any other thing that could fail? It may just be a broken or shorted wire? I noticed that all the wiring is still encased in the original loom so to the best of my knowledge it has never been touched.