Thought I'd share the good news that we now have AC! I originally described the steps we went through to get here at:
We found out that we have an AC with HEAT PUMP! (This was a very nice surprise!) The FIrefly multiplexer setting for Heat Pump was not set on, so we turned that on. Then tried the AC again. No luck! It turned off after 2 minutes.
We then tested the heat pump function. Bumped the temperature up several degrees and the heat pump came on. We expected it to turn off at 2 minutes. It didn't. Then we tried the "Auto" function for the heat pump. There's a fair delay on it, but after 2-3 minutes it turned on again, and shut down when I reduced the desired temperature to the thermostat value.
This time, we set the temperature lower than the thermostat value and kept the switch on "Auto". After 3 minutes, the AC turned on. And STAYED ON! Must have been a sticky valve perhaps?
Anyway, problem is resolved. One very happy camper here!