UPDATE: With the help of forum members, we have determined the problem to be within the climate control head unit not sending power to the heater control valves. I have ordered a gently used climate control head from E-Bay and will swap it out when it arrives. If that solves the problem I will then take apart the bad unit to see what has failed (but presume the problem is with faulty connections between the circuit boards as shown in the forum link provided by onehundred80). Thanks for the responses and assistance. I'll let you know how this turns out. Then I'll try to fix the problem with the ambient outside air temperature.
Bob Davis (Red Dog)