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Two HVAC systems (Air Handler + AC & Hot Water) One Thermostat?

iced98lx Member Posts: 68
edited July 2021 in Thermostats and Controls
Hello everyone! I've tackled a job I had been meaning to get to which was pulling the control wires for the AC through the wall into our master bedroom into the same hole as the wire coming up from my TACO zone controller for the heat for the bedroom zone.

The plan was to run a single thermostat to control both, I'm learning that may not be feasible but I'll take input on how to handle it.

Wires available to me from the AC:
Red (Transformer)
Green (Fan)
White (AC)

Wires available to me from the Heat:
Red (transformer)
Green (Common)
White (Zone)

Thermostat I'm trying to use: https://www.luxproducts.com/wp-content/uploads/2018/08/180803-KONOzManual-updated.pdf

I took an initial stab as such:

ACGreen (FAN) to G (FAN)
ACWhite(COOL) to Y1
HeatGreen to C
HeatWhite to W1
HeatRed to RH
Removed RH to RC Jumper

Unit booted up, ran through setup fine.

Set it to kick the AC on, it did, smoke immediately began pouring out of the back of the unit, I pulled it off the wall.

Burned a resistor off the board. Put batteries in, booted up. Removed all heat wires and put RC to RH jumper back on, hooked it up, running AC just fine now.

Is the common wire coming from my TACO zone controller just a no-no and I need one from the air hander?


  • Zman
    Zman Member Posts: 7,569
    Any chance you could find a schematic for the t-stat?
    It is hard to say without more info ut it sounds like it is getting power from one of the AC wires and would need a common from the same source if you don't want to use batteries. If you remove the jumper and wire the Taco to Rh and W1 with no common does it work? Another option would be to fire it up on batteries and use a multimeter to figure out how it is set up.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • mrhemi
    mrhemi Member Posts: 28
    You let the "Factory Smoke" out.
    Licensed Steamfitter.
    Licensed Instrumentation & Control Technician.
  • ratio
    ratio Member Posts: 3,624
    Put your meter between the red wire from the AC & the red wire from the zone controller. I bet you'll see about 50 volts. The two transformers are out of phase. Easiest fix would be to swap the secondary wires around on the transformer in the air handler. Double check afterwards!

    & replace the thermostat. Once the smoke comes out, it's done.