[lsaferite]

Heatpumps are essentially pretty dumb devices at core. They use 24v AC for control, there's a reversing valve contactor to control if it's heating or cooling, there's a contactor for the fan, and one for each stage of the pump. Maybe there's another contactor for the emergency heating element. If you are fancy you might have contactors for UV sterilization, humidification, and/or dehumidification.

Literally the 'smartest' part of my HVAC system, beyond the thermostat, is the blower fan. It's a variable speed motor and has a speed controller integrated into the motor housing with multiple 'taps' that let you control the fan speed in steps. It's configurable if you have the programming hardware.