How does this home HVAC system work??
 

Can’t figure this out, my Google is weak on this one.

It’s an older system, maybe 15 years or so?

I believe it’s a single system, split between the upstairs and the downstairs (so each can be controlled separately).

Here’s the controls. Pictures are upstairs control, downstairs, and a third box mounted in a closet.



http://forums.pelicanparts.com/uploa...1679541420.jpg
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The issue I’m having is sometimes the blower fan randomly goes on. It’ll run for a while, then shut off. There’s no heat or ac when it does that, just the fan.

There’s no pattern that I can tell.

It seem like the way I have the levers set, the system should be “off” and not do anything.

I even shut off the breaker labeled “A/C” and the blower still does its random thing.

Can’t figure out if I’m doing something wrong, or there’s something broken/wrong in the system.

The thermostat box is more than 15 years old. My family home had one 40 yrs ago. The closet box may be a newer communicator - I would think the T-stats would be out of the loop.
My Honeywell wi-fi T-stats do turn on the blower for 'recirculation' 35% of the time and at a lower blower speed - uses little relative enrgy and balances out the room temperatures. Fan settings are Auto - ON - and Circ etc.

The AV breaker will only cut out your outdoor AC condenser unit. The furnace fan is powered by 120V and located separately.

I am glad to answer early - none of what I said is wrong but won't be an helpful as others!

It looks like the Trolatemp Total Zone is a sharing system and should have a damper to direct air to two different zones.
I found the manual online and will try to find it through the honeywell site when I get to work.
Those Chronotherm stats were available when I was doing commercial work over 30 years ago...

I'm not familiar with the specific hardware, but my guess is NMT has it. THere are HVAC controls that will tell a system to "move the air around a little bit every once in a while" which is especially useful when there's an upstairs and downstairs (hot air rises). My experience is what NMT says, you can set some systems to circulate the air X% of the time. What that usually means is "even if the HVAC hasn't run, every hour or every 30 mins or every X-time, kick the fan on for <percent of X-time, 30% of 1 hour would be 18 mins>. In our old place, that was super useful in the time of year (spring and fall) when we didn't need the AC but without the fan, the upstairs/downstairs temps could end up 5-10º different.