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Started By
Message
PSA For anyone looking to install a smart thermostat or Nest
Posted on 6/22/21 at 2:08 pm
Posted on 6/22/21 at 2:08 pm
Just FYI to anyone wanting to install a smart thermostat...
DO NOT INSTALL ONE WITHOUT A COMMON WIRE.
I learned this the hard way with a Nest and paid the price. Luckily it was just the thermostat, board, and contactor that needed to be replaced $$$. I have read up on people having issues with it short cycling the compressor to the point where it runs backwards and that's an immediate failure. The sad thing is Nest even has the installation procedure for a installation without a common.
Without the common wire, the nest uses the power on the "Y"&"Rc/h" to charge the battery. Some if the HVAC controllers see ANY power flowing between those terminals as a request for cooling and turns on the system....at that point there is no power for the nest to charge since the compressor is on and the nest stops power stealing and the hvac control board sees no power draw and turns off the system...at that point there is power available for the nest to charge and the cycle repeats.
If you do not have 5 wires don't install the nest.
DON'T DO THIS
Make sure your install is like this.
DO NOT INSTALL ONE WITHOUT A COMMON WIRE.
I learned this the hard way with a Nest and paid the price. Luckily it was just the thermostat, board, and contactor that needed to be replaced $$$. I have read up on people having issues with it short cycling the compressor to the point where it runs backwards and that's an immediate failure. The sad thing is Nest even has the installation procedure for a installation without a common.
Without the common wire, the nest uses the power on the "Y"&"Rc/h" to charge the battery. Some if the HVAC controllers see ANY power flowing between those terminals as a request for cooling and turns on the system....at that point there is no power for the nest to charge since the compressor is on and the nest stops power stealing and the hvac control board sees no power draw and turns off the system...at that point there is power available for the nest to charge and the cycle repeats.
If you do not have 5 wires don't install the nest.
DON'T DO THIS
Make sure your install is like this.
13
Posted on 6/22/21 at 2:23 pm to Pintail
I did the same thing.
Blower motor died and $450 after replacing that, paid the HVAC tech to run a common wire and install my Nest thermostat to avoid any other issues. He noticed I already had a common wire tucked away in the wall
Said he didn't think wiring the thermostat without the common wire would have killed my blower motor, but was too much of a coincidence for me. Maybe he was trying to make me feel better.
Blower motor died and $450 after replacing that, paid the HVAC tech to run a common wire and install my Nest thermostat to avoid any other issues. He noticed I already had a common wire tucked away in the wall
Said he didn't think wiring the thermostat without the common wire would have killed my blower motor, but was too much of a coincidence for me. Maybe he was trying to make me feel better.
Posted on 6/22/21 at 3:38 pm to Pintail
Mine is installed like the one on top. Didn't have a common wire when I installed. I'm replacing my system soon, I guess have the guy run a common wire when I do that?
Posted on 6/22/21 at 3:49 pm to Pintail
You can also have your R wire in the Rc slot
Posted on 6/22/21 at 6:56 pm to Pintail
I installed a Sensi and figured out my common wire was ran to the thermostat but wasn’t wired in inside the unit. Fun times figuring that out and wiring it in on a weeknight sweating in the attic.
Posted on 6/22/21 at 7:56 pm to Pintail
Interesting... bookmarked for later.
Posted on 6/23/21 at 6:55 am to TigerDeBaiter
It’s usually in your wire pack, I’ve installed 4 of them and just go in the attic and strip the wires back and add it in
Posted on 6/23/21 at 7:10 am to Pintail
So if I don’t have newer wiring without common wire, pull new wire and rewire?
That’s good information I have heard this in the past and have know people do the work around had issues but your post is simple enough
Thanks
That’s good information I have heard this in the past and have know people do the work around had issues but your post is simple enough
Thanks
Posted on 6/23/21 at 7:57 am to MAUCKjersey1
quote:
You can also have your R wire in the Rc slot
You mean instead of running a common wire ?
Posted on 6/23/21 at 8:18 am to Cracker
quote:
So if I don’t have newer wiring without common wire, pull new wire and rewire?
As far as I understand, yes. Also as another poster mentioned, an extra wire may just be tucked behind the wall and not hooked to the board. Older thermostats did not need them, so many techs would just tape them off and put it behind the wall. You can check there first before running a new wire.
Your board should have a location to hook up a common wire. For now, I just hooked up a standard battery operated Honeywell thermostat while I do a little more digging on smart thermostats. (my old Nest was fried anyway)
This link shows you how to check and steps to take. Just FYI, I am not professional in this field, just a DIYer that is trying to keep others from having my same issue.
Thermostat C wire Explained
Posted on 6/23/21 at 9:12 am to Pintail
quote:
Older thermostats did not need them, so many techs would just tape them off and put it behind the wall. You can check there first before running a new wire.
I installed one at my parents house that was built in the 90s and it even had one that just wasn’t installed. There’s a bunch of YouTube videos about it
Posted on 6/23/21 at 9:50 am to Pintail
I did not have one for a long time. Only issue was, Nest needed to be charged once.
Posted on 6/23/21 at 10:26 am to Pintail
I’m surprised they make some smart thermostats that have their own power source. My Honeywell thermostats will not power on unless the common wire is connected.
If you look at older electronic thermostats, most of them have their own power source, usually a few AA batteries. Even older mercury thermostats have no power source since they are mechanical. But if your smart thermostat does not have its own reliable power source, connecting the C wire gives the thermostat the 24V it needs to operate.
Good post. Everyone with a smart thermostat should be utilizing the 24V from the board.
If you look at older electronic thermostats, most of them have their own power source, usually a few AA batteries. Even older mercury thermostats have no power source since they are mechanical. But if your smart thermostat does not have its own reliable power source, connecting the C wire gives the thermostat the 24V it needs to operate.
Good post. Everyone with a smart thermostat should be utilizing the 24V from the board.
Posted on 6/24/21 at 4:36 pm to Pintail
There are 2 types of Nest thermostats. 1 is smart and costs like $200. The other is a basic thermostat that has a nice clean glass/mirror finish. That one is $99
I really like the $99 one and have had zero issues. Easily replaced my old 1999 thermostat with the $99 Nest
I really like the $99 one and have had zero issues. Easily replaced my old 1999 thermostat with the $99 Nest
Posted on 6/24/21 at 10:18 pm to Man4others
Get a Honeywell and thank me later.
Nest is garbage.
Nest is garbage.
Posted on 6/25/21 at 1:08 am to Baers Foot
Whoa. I've gone through a blower motor and two contactors. With a four wire set up.
Two weeks ago my pcb went out. I childhoods get a new one quickly. So I bypassed it with a contactor. I'll make sure to add that 5th wire asap.(I think it's already in the wall.
Yep, just checked on the app.
I need to fix this.
Two weeks ago my pcb went out. I childhoods get a new one quickly. So I bypassed it with a contactor. I'll make sure to add that 5th wire asap.(I think it's already in the wall.
Yep, just checked on the app.
I need to fix this.
This post was edited on 6/25/21 at 1:12 am
Posted on 6/25/21 at 2:33 pm to Pintail
I had a nest at my old house and installed it without the common wire and after about a month my unit started acting weird. Short cycling and the outside unit would come on and not the blower or the blower would kick on and off. Hooked up the common wire and it worked fine for the next 5-6 years. Just finished building a new house and I gave my old nest to my brother. His unit doesn't have a common and now the thermostat will not even let us set it up with out hooking up the common. So I'm wondering if Nest did some kind of update that makes you hook up the common now.
I just pick up 3 Honeywell T9's this morning to put in the new house. Can't wait to get them installed this weekend. I'm tried of getting up and going adjust the thermostats or coming home and we forgot to raise the bedroom stat from our sleeping temp.
I just pick up 3 Honeywell T9's this morning to put in the new house. Can't wait to get them installed this weekend. I'm tried of getting up and going adjust the thermostats or coming home and we forgot to raise the bedroom stat from our sleeping temp.
Posted on 6/25/21 at 3:06 pm to Pintail
I've installed multiple ecobees in different homes. All with a common wire, but I swear not a single one was simple like the examples they give you in the instructions. Always one wire that is doing some goofy shite back there. I have bad luck there but I've always guessed right on where the wires go.
This post was edited on 6/25/21 at 3:07 pm
Posted on 6/25/21 at 8:48 pm to Pintail
Had two units in my last house. My downstairs worked perfect with the nest. My upstairs - didn’t work out. I even rewired it. No dice. Eventually stuck a plain ol $20 Honeywell on it and it worked fine. I recall thinking the common wire being an issue and that’s why I rewired it.
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