AC and HEATER FIX
Cliff Notes:
Except for the AC button, ST165 AC and non-AC heater control panels are the exactly the same
1986-87 pre-facelift heater panels are not interchangeable with 1988-89 ones.
My HVAC panel with AC crapped out again and nothing was available at the junkyards. I had a spare HVAC panel without AC but I got to thinking; to speed production Toyota probably made the same circuit board with just a block-out button for non-AC cars, right? So I took apart both an AC panel and a non-AC panel and guess what? The internals are both the same.
You can simply remove the block-out button and swap in your AC button and you'll be good to go. (I had disassembled everything so I swapped the circuit board into my panel with the AC button.)
So this broadens your options if you can only find the non-AC panel and your car has AC.
CAUTION: be extremely careful if you're removing the second circuit board. It is attached to the LED's with 2 delicate plastic prongs on each side of the LED's - they break easily.
Below: the non-AC heater control panel vs AC panel.
Below: comparison between the AC button (left) and block-out button (right). Those four legs prevent the block-out button from being depressed.
Below: use extreme caution if removing this circuit board from the shell casing!
Below: this is the disassembled 'non-AC' panel. Lo and behold, underneath the black block-out button, you can see it does indeed have the AC switch. Also a good view of the fragile LED prongs and internals.
Below: another view of the internals
Below: test run to see if the AC button will work....
Below: the AC works!
*HEAT SLIDER BAR*
This last pic is something that's been plaguing us 4th Gen'ers for a long time. I believe I've finally identified which leads go to the heat slider bar - they are the No. 1 and No. 10 Pins. If you resolder all the red circled points, it should fix your heat. If you try it and it works for you, post feedback