I just installed an ecobee 4 and I have a C-wire so it seemed straightforward. The ecobee shows that it detected all the expected wires. However when it tries to call the AC it instantly restarts every time. The heat and the blower work, and the AC worked with the old Honeywell analog thermostat.

I read somewhere that newer equipment can be sensitive to shorts even when older equipment works fine. Could this be the case? How would I diagnose? I just moved into a condo and don't know how to access the control board yet.

Old wiring

Ecobee shows all the wires detected correctly

  • I see the"C" label on the old 'stat, but I am concerned it may not have the modern smart 'stat meaning of the term. Why did the old 'stat need a C wire/constant power? Onboard computer? Backlight? – Harper - Reinstate Monica Jun 3 '18 at 13:06
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    Can you post photos of the wiring at the furnace/air handler end? – ThreePhaseEel Jun 3 '18 at 13:11
  • @Harper yes the ecobee has no battery so requires either a C wire or something they include called a power-extender kit. No idea what the old stat would have needed, it was an analog Honeywell with sliders, nothing digital. – emkman Jun 3 '18 at 17:21
  • @ThreePhaseEel just moved in to this condo, only thing I can find indoors is the stat and the circuit breaker. About to hunt for the air handler in the shared garage/backyard. – emkman Jun 3 '18 at 17:23
  • Someone on reddit commented: "Apparently the current draw is too much for the 24VAC transformer in the air handler. Consider replacing it with a new transformer that has a higher VA rating." Any thoughts on this? – emkman Jun 3 '18 at 17:23

I talked to my landlord to inquire about access to the actual equipment and it turns out its on the roof and not happening. However, he said he had the same problem with his unit and his Nest and to solve it he just removed the C wire. A big difference between the Ecobee and the Nest is that Nest has a battery and therefore does not require a C wire. I got one, wired it up with the same config as posted, minus C wire, and it was able to call the AC right away. Some commenters mentioned that my C wire might not actually do what it is labeled as, but it did power on the Ecobee. So either I had a bad Ecobee or it isn't able to handle certain funky situations that the Nest can. Maybe the lack of C wire affects the current draw, but hard to say since I never accessed the equipment.

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