Weird T-Stat/Zonecontroller issue

Discussion in 'HVAC Heating & Cooling' started by RhoZeta, Nov 1, 2019.

  1. RhoZeta

    RhoZeta New Member

    Nov 1, 2019
    Fort Worth
    Having an odd problem that I can not figure out and searches for similar issues turn up nothing so I am posting to the forum in hopes that somebody has seen this before.

    Equipment and setup;
    Trane 5 Ton Heat Pump unit in a 2 story home, using a Honeywell 3 zone controller, (Only uses 2 zones) for upstairs and downstairs. Have two Trane (Honeywell) T-Stats, one upstairs one downstairs with only difference being upstairs T-Stat can also control Emer Heat (Heat strips).

    About 1.5 years ago, came downstairs one morning to the A/C blowing and T-Stat said it was 56F, tried shutting it off at T-Stat and no response. pulled T-Stat off the wall and it shut down. Found the 3 AA batteries leaking acid, upon opening unit found that the acid had damaged the control board. Entirely my fault for not changing the batteries. ( I no longer put batteries in them, system has a power wire, really no need)
    Went to the HD and found a new Honeywell WIFI T-Stat, I think it is a T-5. Installed unit, worked fine except that the A/C would run in A/C or Heat. Did some Trouble Shooting and changed the O wire over to a B system with T-Stat programming changes as well and after that the heat pump would run with heat or A/C called. Spent a frustrating few days trying to figure it out,called the worthless Honeywell help line and they had no clue how to help.
    In TS I can touch the bare wires together and it will call for heat pump and A/C respectively, the upstairs T-Stat works as it should as well.
    Tried another Honeywell T-Stat that is identical to the Trane T-Stat except it is Honeywell branded and same results. In frustration I ordered an identical Trane T-Stat as the damaged one and the problem persist.
    Also in TS I moved the T-Stat and damper from Zone 2 to the unused zone 3, thinking there was possibly an issue with the zone controller and the problem persist.

    In summary;
    I can individually call for A/C and heat using the wires at the thermostat and it works fine so I am assuming wiring from T-Stat to zone controller is good.
    I switched the T-Stat and damper wiring from zone 2 to the unused zone 3 and problem is same.
    The system runs as it should from T-Stat upstairs, set it to heat, heat pump comes on, set it to cool and A/C comes on.
    Zone controller is not indicating any faults and it displays properly with each call, red LED lit up for heat, yellow LED lit up for A/C with condensing unit responding accordingly.

    T-Stats used;
    Honeywell T-5 Lyric WIFI, Performed setup per instructions including equipment selection (1 C 1 HP)

    Honeywell RTHD8500, identical unit to the Trane that was in use before problem.

    Trane TCONT8000, IS the identical part number as the original unit.

    I am game for thoughts and suggestions, thank you.
  2. WorthFlorida

    WorthFlorida The wife is still training me.

    Oct 28, 2009
    Orlando, Florida
    How many wires to each thermostat? Any pictures? I'm having a hard time trying to read into what your problem is? Its possible the two thermostat do not have a common ground.
    Last edited: Nov 5, 2019
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  4. WorthFlorida

    WorthFlorida The wife is still training me.

    Oct 28, 2009
    Orlando, Florida
    I think I found the issue, the AC runs in AC mode or Heat mode? No Heat, correct? Check the O wire and the programming of the thermostat. For AC you want power on the O lead, for heat pump no power. A valve operates outside at the compressor. The thermostat must know the type of heat and single stage or two stage.
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