I need definitive heater valve and AC expansion valve answers

You need to do some diagnosis to determine that
Do you have a 1969 Body service manual with all the diag info?

Last I heard, you couldn't easily get any of that stuff for the Lincolns and T birds
We used to switch them to A/C in the summer and back to heat in the winter

The heater hose valve should be closed when you engage the AC function. Those valves are available from multiple sources; my favorite is NPD. If you’ve replaced all of those parts, pulled a vacuum long enough to remove all of the moisture in the system and to verify you have no leaks, and then filled the system with the bright amount of refrigeration, then you have a complete system. Usually, expansion valves do not need to be replaced; they don’t wear.

Now, an R134 system has a lower efficiency rating than an R12 system. Most 134 systems require a much larger condensor in order to gain back some of that loss. But most cars cannot accommodate that. So, to achieve the best results, you have to eliminate that big heat source in the plenum. If you’re not sure on what heater valve you need, call the guys at NPD and they’ll help you.

Good luck.