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Thermostat compatibility - old furnace

towerhogtowerhog Member Posts: 2
edited March 7 in Controls
I was trying change out a thermostat for a 200BA88 Bryant furnace -
there are 4 wires however only 3 are used: W B R. Even though the photo shows the green connected to the old stat, it connects to nothing.
the wireless smart thermostat software has become more trouble than its worth and we wanted to put on a simple 7 day programmable - no wifi
.
The stat I tried is the Honewell RTH7560e.
The previous stat was connected with Blue to B White to W and Red to Rh (jumpered with Rc) and it worked fine. When I connected the Honeywell Blue to o/b White to W and Red to R, the valves opened and the burners ran constantly, (even though the temperature was not low enough to turn heat on) and it didn't shut off until I turned the breaker off.
Tracing the wires to the R182c relay and the furnace controller the white wire goes to the fan limit switch then to the W on the relay and the red and blue go to the R and B on the relay.
I have attached some photos
Is this a compatibility issue?
thanks for your help...
The relay:

The contol and limit switch

The new mounting system

this is the stat we want to replace

Comments

  • SteamheadSteamhead Member Posts: 13,822
    That's an old Series 10 relay, which used a unique wiring hookup. Try disconnecting the red wire at the thermostat and moving the blue wire to R. Test it, and if I'm right and it works, cap the unused wires (Red and Green) at the thermostat so they won't accidentally touch something.
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  • towerhogtowerhog Member Posts: 2
    Thank you very much. It is working perfectly now.

    Out of curiosity, why do you think it worked as wired with the thermostat in the pic but not with the new one?

    Thanks again!
  • Big Ed_4Big Ed_4 Member Posts: 1,344
    edited March 8
    The old Series 10 controls used the R terminal to power a heater in a series 10 thermostat . The early heat anticipator . The white and blue terminal on a old series 10 contol is our modern TT connected to Rh and W on thermostat
    I have enough experience to know , that I dont know it all
  • mattmia2mattmia2 Member Posts: 1,318
    the terminal in that older t-stat that the blue wire was connected to wouldn't close unless it was set in heat pump mode and was calling for backup heat
  • Big Ed_4Big Ed_4 Member Posts: 1,344
    edited March 8
    You need now check which two wires are good to uses to connect Rh and W and to connect to W and B on the control using an electrical meter . Forgetabout the R terminal on that old series 10 control it is not used .
    I have enough experience to know , that I dont know it all
  • EdTheHeaterManEdTheHeaterMan Member Posts: 572
    edited March 13
    on the old series 10 thermostats,
    there were 2 circuits within the thermostat in order to keep the boiler or furnace from short cycling. W and B contacts needed to "Make" contact in order to start the burner or circulator. W and R would keep the circuit closed to maintain operation until the W and R contacts opened indicating the thermostat was satisfied.

    If you look at the diagram you can see the contacts at the red arrow are further apart. The contacts at the blue arrow are closer together. R to W would not bring on the control. When W and B circuit is completed the burner would start. As the temperature would rise W and B would open but W and R were still closed allowing he burner to continue to operate until the temperature increased enough to open R and W satisfying the call for heat.

    The way we remember which wire did what...
    W to B is Will Begin
    W to R is Will Run

    Are there any other old-timers that remember that mantra?
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