Cliff Notes:
Except for the AC button, ST165 AC and non-AC heater control panels are the exactly the same

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 and block-out button. 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!

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

- Check the the solder points where the 2 white and blue female connector plugs join the "piggyback" board. The act of removing and replacing and/or pressure on the backside of the HVAC panel can create stress cracks on the solder joints.

- If the lights flicker or don't work at all on your HVAC panel (the little men icons or slider bar), simply check the bulbs. They are bayonet bulbs that simply twist out counter-clockwise and I found mine weren't making full contact to the circuit board. Create better surface contact with some electrical tape, a tiny bit of solder or best yet, get some new bulbs.