Neil,
Good point. There are more factors other than the CV1's, This is my test tank. This is where I have the wet/dry 5/16 to the tap hole. The wet lines are 6 years old. the dry are 2 years old. The bush faces east. Despite my lack of success with the wet / dry tap hole I did see twice this season when the wet 5/16 lines had ice in them and the dry 5/16 were able to run the sap.
Sap ran just fine today. I decided to wait until tomorrow to process the sap. It is 34* so figure that the sap can't get any worse than it already is. My only concern is having the evaporator turning ropey. That would be a waste. Chance I am willing to take to enjoy a night at home.