I moved to a new home last winter. I have a PTAC unit. Fan is working well, same with the heat over the winter. The building has changed the building's system to cooling for the summer but unfortunately I'm not getting any cold air out of the unit, only the fan blowing ambient air through the unit. I removed the thermostat and I'm seeing two wires that are not connected but I can't seem to be able to find if that can be the issue. It seems orange and yellow wire can be related to cooling, but when researching it seems the wiring color is not standard (e.g. blue for Y1?). Does the picture make sense to anyone? I'm thinking those two wires are probably the culprits! Thank you for your help! Thermostat

  • Does the building have a maintenance man/service you can check with? Maybe check a neighbor's thermostat.
    – JACK
    May 21, 2021 at 14:40
  • Can you post photos of the wiring at the furnace end please? May 22, 2021 at 0:27

1 Answer 1


It's fine that the orange and yellow are not connected; this assumes they are not connected to anything inside the furnace.

Running 7 wires for a thermostat is normal for future enhancement of either your HVAC system or the thermostat itself. The additional benefit of running too many wires is that if there is a faulty or broken wire like red then you can just repurpose a different color without running a brand new t-stat wire. If you only ran 5-wire and red turned out to be faulty then you need to run a whole new wire; hopefully 7-wire this time ;-)

Yes, there are generally accepted colors for stuff but there's nothing physically wrong with using "wrong" colors as long as they land in the correct terminals at both ends of the wire.

You'll notice there's some gray tape on the blue wire which is a standard wire color for cooling in an A/C unit. The yellow should have been used but whatever.

The only way to truly know which wires go where is to read the manuals: thermostat, furnace, and A/C unit. G needs to land on G at both ends of the wire regardless of wire color.

To me everything looks fine here. You need to add pictures of the wiring inside the furnace and in the A/C unit. If you're not able/willing to do this then you need to call a professional.

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