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Discussion Starter · #1 ·
Hi all, I am replacing a Honeywell thermostat with the ecobee4 smart thermostat, but after installing the new unit inserting the main breaker back on, the thermostat screen is not turning on.

Background:
When I took off the Honeywell unit I noticed that the blue wire was tucked behind the others and the unit was receiving power from two double a batteries. I connected the blue wire to the C port of the new unit.

Troubleshooting So Far:
-All five wires appear to be in snuggly as I gave a gentle tug and they do not move.

-I hear a click when I push the faceplate on, so it seems that the pins are connecting.

-I researched the ecobee support site for this model, and it does say to connect the red to RC and not RH.

-I waded through the dust and spider webs in my basement and took off the AC unit's cover plates. From what I can see there are wires going into the C and R ports down there as well. I am attaching pictures in case I'm not seeing correctly as I am a total noob of course.


-When I am attempting to power up of course the main breaker is on, the switch on the AC unit is in the on position, and the only switches that I could see on the inside of the unit were in the on position as well.

-I read that the drainage switch could be a potential issue if it had tripped at some point. I saw the tubing on the side but I didn't really understand what the drip tray would be I guess maybe it's on the inside of that? Anyway I could not see some kind of switch on that thing but I did attach a picture case I'm just missing it. Also the AC unit was working last season although I did not actually try to run it yet this season but it should be working fine.

-As a test I reconnected the honeywell unit, took out the double a batteries, and used the C wire instead. Interestingly I could hear the fan turn on when I turned the switch on the thermostat, but I was not getting a display either on the old unit (we were getting a display when using the batteries). So I'm thinking maybe that means the problem is with the C wire? I know we have a voltage tester somewhere in the basement keyword there being somewhere. Assuming I can find it I I'm not sure if I would test the C wire on the AC unit itself or on the wall mount where the thermostat is or both. I have read you need at least 24v...we did get a brand new electrical panel installed and certified a year ago so I would be surprised if we have an internal problem although the AC unit was installed by flippers a couple years prior to that and the flippers cut some corners so I would not be surprised to learn if there is something related to that. Anyway I'm hoping it's not so much that and rather that is just me the noob not understanding what I'm doing and there being some simple solution. Does anyone have ideas of further troubleshooting I can try? Thank you so much in advance for any assistance you can provide.
 

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Discussion Starter · #3 ·
I would say that the blue wire from the thermostat cable needs to go the C terminal in the HVAC unit. I upgraded thermostats some years back in an older home, and I believe that's what they needed.
Thanks for your reply Nick. I was wondering why the wire in the C port on the AC unit was not blue (looks kinda light gray).

There appears to be a blue wire to the left of the pic I'm attaching to this reply (hard to tell from the pic, as I took this earlier and am not looking at the actual unit at the moment, but I think it's just not connected to anything--actually it looks like the green ad yellow wires are also not connected, which is confusing because I thought the unit was working before).

So if that seemingly unconnected blue wire on the left side of the pic is indeed the other end of the same wire from the thermostat, are you saying I would replace the light gray wire that is currently in the C port on the AC Unit with the unconnected blue wire? And in that case, what do I do with the light gray one that I would be pulling out of the port? (maybe put one of those little plastic caps on it, or is it necessary for something else?).

Thanks so much.
 

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So the system I converted my thermostats was heat only, but here's what I think you've got.

The cable with only the blue wire wrapped around it would be your thermostat. That blue wire should connect to C, along with whatever is connected now. The other brown cable, I believe, would go to your compressor outside. As for that gray cable, dont know what it's for, but if it all worked, I'd leave it alone and keep it connected.
 

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I concur with a re-statement. The wire previously attached to 'C' on board stays. It is likely going outside to compressor.

The curled up blue wire gets uncurled, as Nick stated, striped and also gets to attach to the 'C' terminal on board. Looks like your blue to 'C' at thermostat is attached.

This 'C' terminal now will provide 24V all the time instead of just when on call, on other color coded wires.

You are good to go. Lastly, pay attention to your settings, gas vs electric etc and whether 2 terminals are jumped by default or need to be jumped. Many today use a computer board type jumper on the back.
 
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