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  1. #1
    Join Date
    Jan 2001
    Im having a problem with a honeywell tz-4 zone controller.

    Using the TZ-4 with a honeywell T8511-M thermostat. Everything works fine except when in emergency heat the board makes the Y circuit on the output side of the board energizing the energizes the electric heat and the compressor but not the reversing valve.

    Ive been told that I may need to connect the "L" terminal on the thermostat to the "L" terminal on the TZ-4 board. It is supposed to tell the TZ-4 that the thermostat is calling just for electric heat.

    Anyone have any experience with this board ? I have put in and worked on quite a few of the EMM and EMM 3 boards and have never encountered this "L" terminal.

    On the honeywell papers with the stat the "L" circuit is supposed to be power for "Equipment monitor or Defrost Reset Control"


  2. #2
    Join Date
    May 2000
    Indianapolis, IN, USA
    For some reason when I ask for the manual of the TZ4, it pulls up the TZ3!

    But it says you need a stat that L is energized in EM heat mode. That's wierd cuz as you say, L is normally a fault light. It gives recommend models that do that but the 8511 isn't one of them.

    You may have to use the EM heat switch on the panel or switch stats.

  3. #3
    Join Date
    Jan 2001
    I went back and added ran the "L" circuits from all stats to the zone control and now all works fine....

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