Zoned A/C

[Michael R. Boyett]

I recently inspected a home with a zoned HVAC system, i.e. one AC/Furnace with two thermostats, one up, one down. I explained to the Buyer that either t'stat could set a temperature for their respective areas but that both t'stats needed to be set to the same function, i.e. Heat or Cool. He said fine but what if one t'stat is on Heat and the other is on Cool...what happens? I told him the controller would not allow that but I did not know if it would default to one or the other t'stat settings and ignore the other one. Anyone know for sure? I've looked at a couple of installation manuals but they don't cover this scenario.

[Emmanuel J. Scanlan]

Hey Mike,

It appears that this controller system is much like others I have seen, with one difference. Most others I have seen are going to service the first call for heat or cool operation, regardless of what the other T-Stats are set for. This one actually poles the T-Stats for requests and if there are more than 2 it will service the majority first, i.e. 2 want heat and 1 wants cool then the heat is activated first.

To answer his question, his system with 2 zones will service the first call and then service the second call, even if one wants heat and one cool.

Some zoned system controllers will make provisions to lock out the reversing valves on heat pumps if the system determines that a call for emergency heat strips was needed to fulfill the heat mode.

[Michael R. Boyett]

Thanks Manny...to be honest that hyperlink was just an example, not necessarily the exact controller that was present at the home I inspected. Your explanation makes perfect sense though and I will assume that is the normal operation of these type controllers for future reference and explanation.