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Question about TrolATemp Thermostat

I have an TrolATemp zone control panel circa 1999 which controls the zoning on my hydro-air system.  Here is a link to the wiring diagram ....

<a href="http://www.hvacmechanic.com/forums/resservice/messages/28847.htm">http://www.hvacmechanic.com/forums/resservice/messages/28847.htm</a>

I have a question about the Slave thermostats on this system (TrolAtemp round).  They are 3 wires (R,W.Y) with no fan or heat/AC selection switches.  What told this thermostat to go into either heat or AC mode?  Were singles set via the R,W or Y wires to the subbase  which has switching logic in it to go into the appropriate mode based on what mode the master stat was in (Master Stat uses the B and O wires for this).  I'm also assuming I can replace these 3 wire slaves with a digital programmable, but I'll have to select the correct mode to match what the master stat is in.   It would be nice if there was actually a programmable model out there that could do this automatically like the existing  slaves.


  • John Mills_5
    John Mills_5 Member Posts: 946
    Your main stat

    The main stat setting controls what the slave stat does. When you select heat or cool, even if it isn't running, the main stat sends that info to the zone panel. So when you ask for heat and the main stat is in cool, won't get it.

    You can replace the slave stat with any programmable. If you replace the main stat, it must have separate O & B terminals. That's getting more hard to find these days. They either leave them off to be cheap or put a combination terminal that you select from a setup routine.

    Or modernize the zone panel to one with staging for future use and electronic limit controls. They use any stats and the zones can do what they want.
  • HyrdoAirJoe
    HyrdoAirJoe Member Posts: 7
    Re: Your main stat


    I replaced the old round main stat 10 years ago with a Honeywell 3600 that at the time had separate B and O terminals.  Lux and Ritetemp still make stats with separate  B and O terminals.

    Back to my original question.  With the current old round slave stat, I know the zone panel controls what mode it's in base don the B and O signals from the main stat, but how does the thermostat itself know to act as a heating or cooling stat?  I know this stat has a special subbase, so my guess is, the zone panel uses some sort of electrical signal protocol to set the stat's mode.  Is that correct?
  • John Mills_5
    John Mills_5 Member Posts: 946
    It doesn't know

    The slave stat doesn't know what will happen. If it is calling for heat, it sends a W signal. When it satisfies, it sends a Y signal. The panel knows what is allowed and if it gets a cool signal and the main stat has energized 0, the panel allows the slave to get cooling. If B is energized and the panel gets a cool signal, it ignores it.
  • HyrdoAirJoe
    HyrdoAirJoe Member Posts: 7
    Re: It doesn't know

    So if the stat does not know what mode the master stat is in, how does it know

    to energize either w or y  if the temp drops below (for w) or above (for y)?

    Are you saying if the system is in heat mode, and my slave setpoint is 70 and say, the temp shoots up to 72, it will energize y for cooling, which will get ignored by the zone panel?  Conversely,  If it drops below 70 while in cooling mode it will energize w for heat which will get ignored by the zone panel?
  • John Mills_5
    John Mills_5 Member Posts: 946

    The slave stat sends either a heat or a cool signal to the panel. The position of the heat/cool mode of the main stat decides if the panel will accept the heat or cool call from the slave. If the call is for the opposite mode, you'll get nothing.

    Modernizing to a new panel will solve that. They have done away with master & slave stats.
This discussion has been closed.