Inspected a home built in 2008 with two Carrier furnaces labeled A and B. There were two Honeywell Thermostats in the home. There was also a Honeywell HZ322 zone controller and a Honeywell THS5320R mounted on the side of furnace A. When working with zone furnaces before, never experienced this type of configuration. When operating the thermostats separately, only furnace A would operate. It appeared that both thermostats were connected to the same furnace. Could not get Carrier furnace B to operate from either thermostat. Any idea what to do to get furnace B to operate? Any other information would be great.
Not sure why this set up would need a zone controller, given that there are two furnaces. How was the ductwork separated? Was it separated? The ones I used to install used a common return with separate supplies, one to each zone, typically first floor and second floor, or upstairs and basement. Each furnace has its own thermostat. An older set up I worked on had a single furnace with a motorized damper in a split duct system that could shut the supply air to one or other zone or supply air to both.
I suspect that the zone controller is not necessary, or there is something going on with this system that you did not see. In either case it calls for evaluation by HVAC tech.
Update, following visit to honeywell site, HZ322 is for controlling a motorized damper, so look for it, probably close to the furnaces in the supply duct. Try setting both thermostats to max temp, possible that they are using two furnaces instead of one big one?, one furnace kicks in first for either zone, second comes on when the first can’t keep up??? Just a WAG, I have never seen this. Is it a really big house?, or are both furnaces quite small? Max forced air furnace size is usually 100K BTU output.