Behr A/C switch questions

[mm8991]

I recently updated my carpeting and dashboard cover, and I installed a restored radio. During those projects, I needed to drop and reinstall the Behr A/C assembly from the bottom of the dash more than once to get it out of the way during these projects. After I got everything buttoned up, I reconnected the batteries, and found that the A/C blower fan was blowing at full speed, even though the ignition key was OFF, and the A/C fan switch was in the OFF position. Assuming that I had created a short somewhere, I loosened the four mounting screws attaching the A/C assembly to the bottom of the dash and started pressing the A/C assembly in various places around the switch. I could get the fan to stop for a moment, but then it would quickly restart on its own again. I pulled the unit down completely and removed the screws that hold the top half of the assembly to the bottom half, and I could see arcing around the switch. So I disconnected the batteries and removed the switch to clean it (with electronic cleaner spray) and look for problems. When I removed the switch, I noticed that there was some sort of round device with two red wires and a small (asbestos?) insulator pad that was laying in the switch cavity. It almost looks like the pad was supposed to be an insulator between the round device and the two rivets that secure the resistive wire coils within the switch (I could see the two rivet indents in the insulator pad). It seems possible that if the insulator pad was displaced that I was seeing a short between the round device and the switch contacts. This must be a high current switch, hence the heat-related insulation protecting the plastic housing around the switch.

The switch seems to be working properly on the bench -- the OFF position is an open circuit, and the other switch positions have different resistance levels, which I suspect retards the fan speed in switch positions 1 and 2 (seems logical since the fan speeds are not really much different between 1 and 2).

Can anyone shed light on what I'm looking at, and how it is supposed to be assembled? What is the round device with the two red wires? Is it some kind of thermistor that opens the circuit if the switch overheats? Anything that I should be checking and/or avoiding? Pictures below...

[Scott A]

The disc needs to be glued to the fiber stuff.

Better than anything is a kit that replaces that switch.
It is a rheostat that doubles the fan speed and air flow.
It doesn’t have 3 positions, it is infinite.

Instead of 1. no air -2. no air- 3. then noisy and too much.

You can put it right where it feels good and avoid the noise.
Or go crazy wind if you want.

Do a web search for the switch, I will too to see what it is named.

I found this link:
https://www.pelicanparts.com/techart..._ac_switch.htm

It is a lot of work, but well worth it. You have to do a little here and there to the older systems, to make things fit right.

[mm8991]

Thanks, Scott. I've seen those threads about replacing with a rheostat before. I see that they are usually done on G-body cars (like in the link that you sent); not sure if the schematic is different for an F-body car like mine. (Speaking of that, I need to find a wiring schematic for the early Behr A/C systems...). I'm not opposed to restoring it to original condition. The early system is basically just enough to keep you from sweating even when it's on high!

[911+1]

Had the same issues with the old switches. I ordered a 3 speed AC switch from Amazon. Works great and was inexpensive.

[mm8991]

I researched this option (buying on Amazon), but was not able to find a replacement part that looked identical. I tried looking online at O'Reilly Auto Parts (there is one right next to my garage condo community, and they are great). I found one on their website that looked identical. I picked up the part the next day, and while it looked identical, one of the two coils that act as resistors to reduce fan speed had fewer windings than the original, and the resistance measured on switch position 2 (medium speed) measured higher than the original part. I thought that might be helpful, since the medium setting on the original part was almost no different than the low setting. Here's the important part: When I plugged in the new switch and tested it, on medium fan speed, the coil with fewer windings glowed cherry hot. I tested the original switch, and the coil was hot but not glowing. It's possible that the original switch design used on the Behr system took this into account, which is why low and medium are almost the same.

I was not comfortable installing the new part and returned it for a refund. No need to cause a thermal event. I'll stick with the original switch for now.