I recently bought the Honeywell Lyric T5 Wi-Fi Smart Thermostat - RCHT8610WF2006 and am having a hard time installing it. As far as I can tell, the heating works but the cooling doesn't.

Instead of blowing cool air, the compressor turns on (or at least its fan runs) and it blows air that's a little cooler that the outside air but still way above what it's set to.

Edit: after leaving the thermostat on cool over night I believe the thermostat is running the heat instead of AC because we also left the windows open and the house was hotter inside than outside when we woke up

Below are the current configurations I have:

App settings

  • heating stages: 2
  • cooling stages: 1
  • heating system: compressorHeat
    • I thought we set this to heat pump?
  • Firmware version:

Heater and compressor

Old thermostat configuration

New thermostat configuration

Furnace wiring

  • enter image description here enter image description here enter image description here enter image description here enter image description here enter image description here wire connection
  • The pics of the old thermostat do not help. We need pics of the actual terminal block on the furnace itself. You cannot trust that the proper color codes were followed on the original thermostat installation. Apr 28, 2021 at 1:27
  • Can you post photos of the wiring at the air-handler/furnace please? Apr 28, 2021 at 2:06
  • @TedMittelstaedt are those photos what you need? Apr 28, 2021 at 10:40
  • @mikeLundquist have you checked the reversing valve setting on your thermostat? Apr 29, 2021 at 0:07

2 Answers 2


The O/B switch has to do with heat pumps and which way they are running. Are they bringing cold air in or hot air in? A long time ago there were separate wires, O and B and the thermostat would signal for cooling on O and heating on B. Then they decided well wait a minute we can just use one wire and when it is signalled high we run in heat mode and when it is low we run in cool mode. Of course some manufacturers did the exact opposite so you have to have a way to switch which your system is - either high is cooling or high is heating.


The solution to this seems to be changing o/b on cool to o/b on heat on the newly installed thermostat. If someone else has a better explanation of what this means in HVAC terminology I'll mark their answer as accepted as I only found this based on happenstance and this answer lacks details.

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