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Really need some help. I was working on the wiring of my home air conditioning and managed to mess up the low voltage wiring. I was installing a wifi thermostat and opened the panel to add a blue wire. Discovered a lot of corrosion on the terminals. I took a picture and proceeded to clean each terminal. Well long story short. My photo wasn't clear enough for me to get all the wires back where they belong.

I'm pretty sure I got the thermostat wires correct, what has me baffled is the low voltage wires to run the outside compressor. My thermostat has power, the fan has power, but I can't get the compressor outside to run.

I did some testing, and got the compressor fan to turn on, but it's not making cold air. So I undid the wires.

Question is. I have two low voltage wires that go to my outside compressor. What should the connect to on my terminal panel.

I've attachéd a photo. Notice the two wires on the side to my compressor. It's a trane that's at least 10 years old. It's a electric furnace and single stage ac, in south Florida.

Thank you.enter image description here

  • Can you post a model number or wiring diagram for your furnace? – ThreePhaseEel May 23 '18 at 11:41
  • Is this a heat pump or conventional furnace? – Tyson May 23 '18 at 12:05
  • Can we see the original picture? – mike65535 May 23 '18 at 12:44
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I am guessing B is common in your case. In that case Y and B. enter image description here

I have drawn a line though the terminsals you will not be using since you have straight cooling and are using the air handler like an electric furnace. R goes from the thermostat to the air handler but not the condensing unit as does W1 which is your heat strip. O is not used since you do not have a reversing valve. Y goes from the thermostat to the air handler then carries on to the condensing unit. Note the common 24 volt is labeled B or B/C (this is typical with Trane products). The B is likely labeled C on your wifi thermostat. So C from the thermostat goes to B on the air handler and then on to the condensing unit. It does not matter which wire from the condensing unit goes to B or Y. I hope this edit clears up any confusion.

  • How good is your guess? – fixer1234 May 23 '18 at 8:08
  • If it’s a heat pump it’s likely a bad guess. – Tyson May 23 '18 at 12:07
  • Heat pumps do not have 2 wires. Most of the older Trane/American Standard units called the common B. They went to calling it B/C for a while and now mostly use the common C designation. – user76730 May 23 '18 at 14:17
  • While O has become more standard for heat pump reversing valves there are a lot out there that use B. When B is/was used it was usually reverse logic of O. I’ve never seen a C terminal labeled B— I have seen the blue wire used for C plenty of times. Additionally the other terminals make this look like a heat pump, but the is no O in use. My opinion is B is the reversing valve and this is a heat pump, but OP hasn’t given the model number or wiring diagram yet, so it’s just a guess at this point. – Tyson May 23 '18 at 19:23
  • Google “heat pump B terminal” – Tyson May 23 '18 at 19:27

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