Long story short, I have a custom HVAC system installed. I have a variable speed heat pump, with a third party A-Coil while keeping my furnace for backup. Without going into too much detail, the variable speed heat pump is designed to run at part load for a long period of time, instead of short cycling like standard AC units. The Nest thermostat is not a communicating thermostat so it can't write a set point or write the rate of change of space temp to control the variable speed compressor, so I have an interface that does that. I have the nest set up for dual fuel with furnace designed to kick on at 15 degrees.
First stage cooling or heating is set up through the interface to control the variable speed heat pump which works great. When 2nd stage kicks in the heat pump goes to full cooling or heating capacity. The issue I am having is that in first stage cooling the system is cooling just as it should, holding right at set point. However, the nest actually wants to overcool just slightly so it can cycle the AC equipment, so when I hold right at set point with no change in temperature the nest thinks it needs 2nd stage cooling which it energizes after an hour or two. I don't want this to happen. I only want 2nd stage to engage based on deviation from set point of 3 degrees (which is default). Is there a way in the settings to adjust when 2nd stage engages? Does a nest pro have that capability?
