1986 TMC 102A3 - Defrost Controls

[jraynor]

Hello All,

I am in the process of gathering materials for rebuilding and upgrading my dash. As I am looking at switches and getting the correct functionality, I have come across a DPDT switch that just has Defrost labeled on it. It is an ON-OFF-ON switch. My question is, What is the difference that it controls? Are there 2 different heat functions or is this a fan speed control for high/low? I have a separate switch for A/C and Heat that is the same style, but why have a single switch for 2 different defrost settings?

I have checked all of the wiring diagrams and I don't see a defrost defrost switch. just the drivers A/C switch which is an ON-OFF, the A/C|Heat switch which is a ON-OFF-ON.

I don't trust the manual I have because I have a 1986 and the manual always speaks of, effective 1992 and 94. I have attached the section of the manual that shows the schematics for the A/C and Heat.

[chessie4905]

As I own a GMC, this is only a guess. Probably high and low defroster speeds. Like in a car, sometimes you need as much defroster speed as possible for snow,sleet etc. Or when it is humid in winter with heat on and floors and passengers are wet, damp. Low for other times just to keep windshield clear.

[buswarrior]

X2 high low and off.

Happy coaching!
Buswarrior

[Bill B /bus]

Switch is low-up, off-center, high-down. Low position puts fan motors in series. High position puts motors in parallel, Low is 24V to both motors so that each sees half or 12V. High applies 24V to each motor.

Bill

[jraynor]

Thank you all,

I will make that note and make sure to hook it up correctly when I get my new switch.

Looking back at the schematic and I assume that with the 1992, they upgraded with switch from a high/low to a rotary knob with off, low/med/high so I would guess that explains why I couldn't locate the switch I was looking for

Thanks again,