Thermostat no longer receiving power after replacement | Home Assistant | Page 1

fossil shoal Sep 20, 2024, 3:25 AM

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So I tried installing the Honeywell Home RTH9585WF. Followed the directions, including shutting off the A/C breaker before working on it. As soon as it was all in place, I turned the breakers back on, and it didn't work. Machine didn't even power on. The cables were a bit bent, so I stripped them back and put them in cleanly. Still not turning on. I thought my model was defective, so I replaced it with the old thermostat, and now the old thermostat isn't receiving power either.

What are some steps to try?

The C and R wires are both present, and the Y W and G wires are the other ones there

craggy obsidian Sep 20, 2024, 3:26 AM

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Check if there is a fuse on the furnace main panel, it might be blown.

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If you shorted something that would probably blow and you wouldn't get power anymore

fossil shoal Sep 20, 2024, 3:28 AM

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Huh, one of the furnance panel? My first look I didn't see something like that, though I did turn the only "on and off" switch I saw on and off while troubleshooting. The main one I manually flipped off during work

craggy obsidian Sep 20, 2024, 3:29 AM

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Like wherever the other end of the R/C/G/Y wires go, it should go to a circuitboard somewhere

fossil shoal Sep 20, 2024, 3:30 AM

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Yeah I traced the other end of the wires to the unit itself, they were connected, but I didn't see a breaker anywhere

craggy obsidian Sep 20, 2024, 3:30 AM

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not a breaker, but a fuse is small

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it'll be a little blade fuse or a cylinder

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I'm just guessing

fossil shoal Sep 20, 2024, 3:30 AM

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Huh, lemme go check again

craggy obsidian Sep 20, 2024, 3:30 AM

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38f3bbb0-556f-4dfe-b659-16be2a1be378.bf19cee7aeaa6ee287042ec5259fdbd3-3626040026.jpeg

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like one of these

fossil shoal Sep 20, 2024, 3:31 AM

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How will I tell if that is blown?

craggy obsidian Sep 20, 2024, 3:31 AM

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with a multimeter if you've got one, or you can maybe just look at it closely and see if the wire is broken inside

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first go see if you can find it and then worry about that afterward

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or possibly something like this

41rpaPJtKxL.__AC_SY300_QL70_ML2_-1620724369.jpg

fossil shoal Sep 20, 2024, 3:36 AM

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I can't really see anything along those lines

craggy obsidian Sep 20, 2024, 3:37 AM

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there with the 3

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pull it straight out from the board

fossil shoal Sep 20, 2024, 3:37 AM

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Pull it off??

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Here's a better look at it

craggy obsidian Sep 20, 2024, 3:40 AM

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it should come right out, it's just 2 blade legs in a socket

fossil shoal Sep 20, 2024, 3:41 AM

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I guess if this doesn't work I'm calling the HVAC guy anyway...

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Lemme flip the breaker off again

craggy obsidian Sep 20, 2024, 3:42 AM

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For more reference: https://www.h2ouse.org/furnace-fuse/

fossil shoal Sep 20, 2024, 3:43 AM

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craggy obsidian Sep 20, 2024, 3:44 AM

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I can't really tell, there should be a very fine wire between the legs visible through the window
If it's broken, it's dead, if it's continuous, it is ok

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Do you have any multimeter to test with?

fossil shoal Sep 20, 2024, 3:45 AM

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They don't seem to be attached... Lemme grab my multimeter

craggy obsidian Sep 20, 2024, 3:45 AM

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yeah just check the Ohms between the legs

fossil shoal Sep 20, 2024, 3:48 AM

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Wow... Yeah the fuse is toast

craggy obsidian Sep 20, 2024, 3:49 AM

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Ok, well at least you know now. Just got to get a replacement from the hardware store.

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or get several 😁

fossil shoal Sep 20, 2024, 3:49 AM

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Why would it blow from replacing a thermostat?

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Yeah not a bad idea

craggy obsidian Sep 20, 2024, 3:49 AM

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it would blow if one of the hot wires got shorted to ground

fossil shoal Sep 20, 2024, 3:50 AM

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I had the breaker off, or at least the one labeled "A/C"

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Maybe I need to shut the entire house's power off next time

craggy obsidian Sep 20, 2024, 3:51 AM

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could be bad thermostat, could be miswired, could be that the lines were still hot and they accidentally touched when you were moving things around (I did this once 😭 )

fossil shoal Sep 20, 2024, 3:51 AM

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Honestly its likely the later... But I'm returning this one anyway

craggy obsidian Sep 20, 2024, 3:52 AM

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Anyway good luck. I'm assuming once you plug in the new fuse it will be back up and running

fossil shoal Sep 20, 2024, 3:53 AM

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I assume so. Nothing else makes sense

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Thankfully its the cold season

craggy obsidian Sep 20, 2024, 3:53 AM

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you can also check for voltage on the terminals with the multimeter

fossil shoal Sep 20, 2024, 3:56 AM

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Well, I'll take the blown one to my local hardware store and see if they have it. Then check others if they don't have it

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So using the ohms/resistance meter checks if they're connected, while the voltage sees if any power is flowing?

craggy obsidian Sep 20, 2024, 3:58 AM

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sort-of

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I'm assuming you have 24V thermostat, so measuring the voltage between R and C should be 24VAC if there's power to the thermostat

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in your case you'll measure 0 since there's no power

fossil shoal Sep 20, 2024, 4:15 AM

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Anything I should know of before getting a new 3 amp fuse? I'm guessing there's lots since apparently its for cars too

craggy obsidian Sep 20, 2024, 4:15 AM

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they come in a few sizes that are fairly similar looking, so just make sure it's exactly the same size

fossil shoal Sep 20, 2024, 4:15 AM

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I'll bring the dead one with me

craggy obsidian Sep 20, 2024, 4:16 AM

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fossil shoal Sep 20, 2024, 4:16 AM

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Are there any other considerations besides dimensions and amp rating?

craggy obsidian Sep 20, 2024, 4:16 AM

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no that's pretty much it

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fuse is a fuse

fossil shoal Sep 20, 2024, 4:16 AM

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I'll learn electronics better someday

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I can wire a network but I guess I can't fix a simple short

fossil shoal Sep 20, 2024, 5:00 AM

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Damn I just realized, does a simple thermostat have enough juice to kill someone?

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I know the furnace itself probably has that

fossil shoal Sep 20, 2024, 7:08 PM

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craggy obsidian fuse is a fuse

All the preparation and documentation and electrical engineering research in the world can't fix a mislabeled breaker...

#Thermostat no longer receiving power after replacement