I just had a variable speed Heat pump installed. It's an Amana unit.

I know the VS is working because I can feel the difference at the registers. My question is this. I have a standard Honeywell focus 5000 thermostat. How does the system know what speed to run the blower? What signal does it get? Does the Thermostat dictate the speed or does the handler have the controls and how does it know what to do?

This is purely a curiosity question.


PS. They are installing a new Honeywell IAQ thermostat next week. (cause I want it)