Update: I purchased a Hot Water Temp control valve thinking that it may be my issue, but unfortunately, I don't think it is the issue. It is hard to see if my existing control valve moves as I change the settings, as Ivan suggested, but I did hook up my new control valve to the plug that was in my old control valve, and when powered up via the dash controls, I could see the valve move to open the control valve to let water in/out of my dash heat exchanger. Once open, no matter what setting I changed the dash air to, A/C or heat, the control valve remained in the open position, letting hot coolant flow through the dash heat exchanger.
In looking at my wiring diagram, the next logical (at least to me) culprit seemed like the Position Control Module.
Any thoughts on this? Anyone know where the heck this Position Control module is, or what it looks like?
Thanks,
Bill