I regret buying a proprietary inverter HVAC from Carrier. The controls are buggy and closed source.
Discussion
I'm not that familiar with inverted HVAC, however from my understanding, most HVAC options (including freeze dryers) are that way, aside from traditional electromechanical systems.
Good news though is that the control systems can usually be replaced with alternatives that can interface with existing relay boards and controls.
I started a project towards that goal by first coding a monitoring system for commercial refrigeration that was combined with a electromechanical thermostat and a hardware defrost clock. Worked great, will post more about it later!
The complication begins with it multiplexes digital signals over existing two copper wires to talk to the other devices: compressor, heat exchanger, thermostat. The wires do a lot more than just on/off. The compressor has multiple power levels and is reversible to operate in heating mode. It can also use a gas furnace as backup.
Troublesome, I am assuming the signals are not documented, as well. What reverse engineering tools would be needed determine what signals have specific meaning? Just a multimeter and/or scope?