Anonymous asked in Home & GardenDo It Yourself (DIY) · 8 years ago

Replace Carrier Thermostat, but two wires within W; what's the purpose of the second wire?

I have a Carrier TB-PHP01 thermostat that connects to an Ecojay SmartZone-2X. I'd like to replace my thermostat with a more advanced one, but I'm having an issue with the wiring.


Y, C, R, G, W, O

The issue I have is, in W, there's two wires (black and white) that are connected together at both sides (thermostat and ecojay at W). What is the purpose of the second wire? It seems a useless wire in my book.


Additional notes:

The house is only a year old and installation came this way. The system is an A/C and heater unit, with an auxiliary heat, and heat pump. The system is electric only and doesn't have any gas or furnace.

2 Answers

  • Anonymous
    8 years ago
    Favorite Answer

    l can't understand why a black wire would connect with w the w is heat the black is usely common i would try leaving the black off

    Source(s): htg clg
  • Greg D
    Lv 5
    8 years ago

    You sound like you're on the right track. You never said whether or not you have a heat pump or just an air conditioner.

    At the bottom of page 4 of this manual it will show you the wiring schematic for both a heat pump and air conditioning. But the furnace/air handler is now your Ecojay SmartZone-2X controller.

    This is the thermostat manual:

    I also found you the PDF for the Ecojay controller.

    It sounds like the white and black wire was there before the installation of the system and was used for a simple heating thermostat which only requires two wires. I'm not sure why they would still be using them.

    Source(s): HVAC/R Service Tech
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