I've searched a lot and can't quite find what how to solve this one. I installed an ecobee smart thermostat, which didn't work with 5 wire connection so I switched to their PEK module with only 4 wires. With this wiring the heat is working fine, but the cooling doesn't (the compressor doesn't kick in, and the fan is blowing ambient air). Anyhow, I tried to map my wiring and this is what I have. Looks wired to me that the Rc is jumped with the common. Any ideas how to fix it? enter image description here

  • Hello, and welcome to Home Improvement. What make/model air handler and furnace do you have? Why is the condensate pump hooked to the thermostat? And, you should probably take our tour so you'll know how best to participate here. – Daniel Griscom Oct 17 at 21:07
  • Thank you for the reply. The model is Trane XB. The condensate pump connection is for a safety switch, so in case of a flood it shuts down the AC completely through the 24v red wire (low voltage). – Gil Cohn Oct 17 at 21:29
  • Is there a C wire between the AHU and the condensate pump? – ThreePhaseEel Oct 18 at 1:24
  • No, there is one between the outside unit and the AHU. For some reason, the C from the thermostat is connected to the R that goes from the thermostat to the pump. I think i need to break this connection and connect the two C's on the thermostat and AHU. Makes sense? – Gil Cohn Oct 18 at 11:34

I have not seen a condensate pump hooked up to the RC wire this looks wrong , the pump should have a level or float sensor and should function with the air handler not running or the thermostat not calling for cooling. The reason I say this is after a cooling cycle in some cases their will be a large amount of water dripping from the evaporator coil so the condensate pump is not normally even connected to the thermostat. I would verify that the yellow is going high when the call for cooling is on.

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