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Upstairs zone heat pump with air handler in attic. Installed April 2022. Thermostat is an Ecobee3 Lite. Noticed this afternoon that Alexa wasn't getting a signal from the Ecobee. I went over to it and noticed that there was nothing on the screen. I went to the intarwebs and saw that in there supposed to be 24-ish volts between R and C. Checked that, bupkes. Went and cycled the cutoffs on the outside and attic units; cycled the circuit breakers at the main panel and on the blower—no change. Called for service, but they haven't got back to me on when they can come out.

Is there anything else I can check or cycle in the meantime?

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I popped open the panel. I measured 240-ish VAC across the bottom terminals, and zero VDC across the top. Transformer stack was warm to the touch, which seems to indicate it's "working" but not outputting voltage. Sounds like Ruskes is in the lead. (I also checked the circuit breaker in the bottom of the box, and it showed 240-ish in and out, so that's clearly fine.)

Now to see if I can source a transformer before the HVAC service call is scheduled.

(FWIW none of the components on the control board appeared to be fried—not obvious tells of heat/burning.)

Apparently these things are a popular Google search—probably not a good thing. Entering "transformer 0130" in the search box pulled up the rest of the number. Found one on Amazon; had to add another item to get same-day shipping.

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  • Did your 24 Transformer die ? usually located in the air handler cabinet
    – Traveler
    Sep 13, 2023 at 23:47
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    @crip659 since the thermostat wires are’t getting any power would a dumb thermostat fare any better?
    – Huesmann
    Sep 14, 2023 at 0:21
  • Have you checked the fuse? It shouldn't pop without cause, but you never know. Often it's an automotive-type fuse right on the main control board inside the air handler.
    – KMJ
    Sep 14, 2023 at 0:21
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    @crip659 without power it's probably not a thermostat problem ...
    – KMJ
    Sep 14, 2023 at 0:22
  • @KMJ will try getting behind the AH panel in the morning.
    – Huesmann
    Sep 14, 2023 at 1:12

3 Answers 3

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Possible causes:

  1. the wires in Ecobee on R or C are loose- you can tug on them to check

  2. The 24 Volt transformer died- Located in air handler cabinet- you will need multimeter to test it. One side has 120 Volt, the other side has 24 Volt

  3. the drip pan overflow protection switch has triggered (and turned off the power) due to high water level, caused by clogged drain

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  • 1. The wires I checked are the ones going to the ecobee mounting plate, basically the ends of the cable from the attic. Nothing inside the ecobee.
    – Huesmann
    Sep 14, 2023 at 0:19
  • @Huesmann, do you know if you ever had 24 volt between R and C
    – Traveler
    Sep 14, 2023 at 0:23
  • @Huesmann If you do not have 24 volt between R and C then the transformer is not delivering it
    – Traveler
    Sep 14, 2023 at 0:29
  • I must have had 24V until today, or the ‘stat wouldn’t have been working.
    – Huesmann
    Sep 14, 2023 at 1:13
2

It did turn out to be the transformer. Swapped the old one out and new one in, and the 'stat fired up.

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Check the condensate drain line. It's probably clogged, and there is usually a float valve wired in to cut power to the system when the float valve is opened by too much condensate.

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  • Not the float valve. Condensate pan is bone dry.
    – Huesmann
    Sep 14, 2023 at 9:47
  • The pan should be bone dry. That's just a backup in case the AC leaks. The float valve is attached directly to the condensate drain line, or in a second line directly adjacent to the primary line.
    – longneck
    Sep 14, 2023 at 17:28
  • Would a float valve cut DC output from the transformer?
    – Huesmann
    Sep 15, 2023 at 1:05
  • Yes, that's usually how it's wired up.
    – longneck
    Sep 16, 2023 at 1:47

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