The temp control lever on my D21 PU is acting up.
sometimes when I slide it all the way to max hot
it loses connection and will not engage whatever is necessary
to return the setting to cool.
After fiddling with it for awhile, it will work again.
I fear that getting behind there to fix anything will be a daunting project.
Any suggestions appreciated.

Pretty much everything in the control panel is plastic. You can remove it inspect to make sure everything is working the way it's suppose to.

You might want to go to the junk yard and grab another one. Make sure you all you can think of. The a/c control panel does wear out over time. Rare but they do.

I can get you a good one if you are interested. I will PM you with a price.

David h.

probably the control head itself, but if your lucky it might be just a cable clamp that came loose/broke

The odd thing is that it is intermittent.
that is to say, it works and then something loosens and though the lever slides it remains in heat mode.

some good suggestions and offers for help here.
can anyone point me to a schemata of the hvac control panel?