While restoring the heat/defrost/fan controls for my project car I knew that the
mechanism had a common issue.
The slide contacts for the three speed fan were melted. I had a good replacement contact piece and intended to just install it in my control panel..
What causes this failure ?
The problem at least partially, is because there is little or no detent feel when moving
the knob from one speed to the next. It is easy to make only partial contact which
causes overheated parts.
Why no detents ?
This is what I found. There is supposed to be a small ball under the leaf spring
of the arm in the second photo. As the arm is moved to the right side the ball is
pushed into the recesses in the grey bar under the arm. This is to provide
proper position for the fan contacts. No ball ? random contact position...
result ?..... melted contacts.
There is no ball in my panel.
Can someone supply the correct ball ?
I hope this long explanation is helpful, I haven't seen it covered.

not sure of the size but maybe a BB would work? they are .177

If the BB doesn't work, you should be able to find a bearing ball that will work here: https://www.mcmaster.com/#steel-bearing-balls/=1ccovbe

Interesting thread. What causes the ball to dislodge? Poor design, vibration, normal wear and tear?

Interesting thread. What causes the ball to dislodge? Poor design, vibration, normal wear and tear?

i have a few spare control units. Will look to see if any are male when I get home.

Hey Ian
Thank you for the offer but I've found a single small bearing in my stacks of boxes and piles of random stuff.

Here's the follow-up.
The ball I found is 3/16" which is slightly larger than the stock hole in the arm.
I have no source for additional balls.....
What to do ?
Grind the rivet holding the leaf spring so that it can be removed intact.
Use a 3/16" drill to enlarge the hole in the arm. Use a 1/8" pop-rivet to re-attach
the spring.
I disassembled my entire unit to thoroughly clean, refinish and lubricate and I
think it is the best way to go. It's very fiddley but the result is fantastic.
I own a NOS control unit to compare with.
I can say confidently this modification makes the switch work better than any
new one ever did. Did you know there are five detents ?
I wish I could post a video.

I was at an Orchard Supply Hardware store yesterday and they had an assortment of ball bearings in different sizes. 4 to a bag I think.
Smallest I saw was 1/16 inch, going up from there.

I think the ACE Hardware near my house has a similar assortment.

I don't know whatyou have locally but it is worth a shot checking local.

Jim