Hvac questions

Im just looking for some insight from HVAC professionals.
So we are getting to the time of year here in Georgia that we may need Heat at night and Air during the day. My question falls with zoning. I have 1 system with 3 zones. The system is all electric.
Dumb thermostat upstairs.
Nest on main level.
Dumb Thermostat downstairs.

Lets just say I set the main level Nest to Heat/Cool setting and I leave the dumb thermostats to heat. I assume the main level thermostat would control the system as in set to heat or cool as needed as well the damper for that zone, while the other thermostats would only control their individual damper?

For instance during the day the nest unit may switch itself to cool and start cooling the main level, what happens with the other two zones that are set to heat? The system can only heat or cool not both?

How do these technologies mesh so the systems knows what to do?

 

Do you have three furnaces and three A/C units?

 

No one units three thermostats. Each thermostat controls a damper to each zone.

 

Honestly it’s not a big deal it’s just me wanting to know how things work.

 

If it’s one system. If the main thermostat is calling for cool while the other 2 are calling for heat, the system will start cooling and the dampers for the other 2 zones should be closed. Once the main thermostat goes into heating the other zones will open to allow the heat into those areas until those thermostats are satisfied.
Now this works if the system has been setup properly with the main floor thermostat being the one in control. If not your unit could actually be trying to heat and cool at the same time. Easiest way to check this would be to feel the temperature of the air coming out on each zone compared to what that stat is calling for or the lack of air if the zones are closed during a cooling call on the main floor while they are in a heat call.