Exactly. The original CEL coming on and ECT registering -40 would have been due to faulty/disconnected ECT sensor but this new problem sure sounds to be thermostat stuck open. You might find that the temp gauge will also drop when driving on freeway for a while which would also point to a thermostat sticking open.

 

I have been keeping a close eye on the temp gage. Drove 80 miles the other night, it stays steady at mid range. Doesn't move a bit. I am going to try and run the AC again on my way home to see what happens.