Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Trol A Temp Replacement wiring

BobbyJ Member Posts: 4
I'm replacing a 20 year old Honeywell Trol A Temp thermostat with a new Honeywell VIsion Pro 8000 (TH8110R1008). The system is conventional forced hot air with a damper set up for zoning upstairs and down. Would seem simple enough but the the new thermostat has a combined B/O terminal while the Trol A Temp has those separated. Can this thermostat be used? How can I wire it to work? I called Honeywell but they would not help me because I'm not a licensed contractor. Perfect. Here's a link to the wiring for new thermostat. <a href=""></a> Thanks.


  • Big Ed_4
    Big Ed_4 Member Posts: 1,758

    You will need a relay at unit for that old system to catch a common or a two way switch... To help understand on your old thermostat..O gets powered to R when switched to Cool . B gets powered from R when switch to Heat .To make automatic ... Program the stat to make O/B used as O .You can connect the coil side of a 24V relay to the O coming from the thermostat and common, Connect Red on the common switched side of the relay , B from zoning control to normally closed and O from zoning control to normally Open ...or program to make O/B to be B and visa versa on wiring .... To make it simple but manual put a two way switch instead of a relay at thermostat
    I have enough experience to know , that I dont know it all
  • SWEI
    SWEI Member Posts: 7,356
    How many wires

    do you have between the stat and the unit?
  • BobbyJ
    BobbyJ Member Posts: 4
    6 wires

    there's a total of 6. No common. But I finally got ahold of Honeywell support and they told me there's no way to wire that thermostat to the old MM-2 zone panel.
  • icesailor
    icesailor Member Posts: 7,265
    Replacement wiring:

    There's a way to wire ANYTHING. You just have to figure out how to do it. It might take isolation relays and other such things but anything is doable. Many of the "tech's" at Honeywell sit in a room full of phone connections with a big book. Like that one that you can get from Taco. If your particular system is old, and there isn't a drawing of your old system going to something new, it can't be done. Their legal department has instructed them to say that. If it isn't in the book it can't be done.

    The biggest problem with doing what might be needed is low voltage and polarity from multiple transformers.
  • Big Ed_4
    Big Ed_4 Member Posts: 1,758

    You can also contact Honeywell zoning , I am sure they can help direct you .... Here is your zoning panel ...its really just a matter of directing power between O and B your heat cool switch did it for you before ..... Good luck
    I have enough experience to know , that I dont know it all
  • BobbyJ
    BobbyJ Member Posts: 4
    Thanks. It actually was the zoning experts at Honeywell

    that told me no Redlink Thermostat could be wired to an MM-2 . Finally found there phone number. I'm sure there is a way to wire it as you and icesailor have mentioned but I might just swap out the zone panel to the modern one. It's probably a bit more expensive fix to the issue but at least I'll be certain of compatibility and won't have to fumble through adding relays etc..
  • John Mills_5
    John Mills_5 Member Posts: 935
    edited March 2014
    0 & B

    That old panel relied on the stat telling it whether it was set to heat or cool by the signal on the O and B terminals. Rare to find a modern stat with both. Last I knew, the White-Rodgers 1F80-361 was a digital programmable that did.

    Probably is time to get a modern panel, make sure it can handle the dampers which are likely powered open & powered closed. A new panel with a discharge air sensor that is ADJUSTABLE lets you cycle the equipment by the panel not the furnace limit.

    If you replace the panel, you'll need to replace the other stat with a model that can select heat or cool manually otherwise the system will never shut off.
  • BobbyJ
    BobbyJ Member Posts: 4

    for the information. I appreciate the insight!
  • npham605
    npham605 Member Posts: 2
    I have the same issue with my TrolATemp thermalstat like your. I would like to replace new master controller and upgrade to Nest 3rd gen thermalstat. Have you find the solution to your re-wire issue? Do you mind to share your solution with me?

    Thank you,
    N. Pham