# FAN Constantly runs with Nest 3rd Generation



## supers05 (May 23, 2015)

chilleblanco36 said:


> Hello all. I'm new to this forum. I just purchased a Nest thermostat. I like it, but I can't figure out why the dern fan constantly runs after the desired temp is reached. Called tech support and they verified it was wired correctly. Thought I had a faulty thermostat, but I got a new one and the same thing happens. This time I didn't even plug in the G wire and the problem still persists. I have a new Rheem 14 seer heat pump that was recently installed before the thermostat.
> 
> I have yellow for Y1, green for G, blue for O/B, red for rh, white for W1, and brown for common. Any recommendations? I really want to use this thermostat. Thanks in advance
> 
> ...


what's the wiring at the unit? 

How did you end up with common? It's not usual to have common in original installations, so I'm expecting that someone either ran a new wire or used an "add a wire" device. Check for another device in the wall and at the unit. 

What was the previous thermostat and did it have a "K" terminal? 

Cheers!


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## chilleblanco36 (Dec 1, 2016)

I had a common on my old unit as well if i remember correctly. I just didn't use the old thermostat. I was here with the guy during the wiring and installation. This happened when I tried the ecobee3 as well. Only on heat if I remember correctly 

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## supers05 (May 23, 2015)

chilleblanco36 said:


> I had a common on my old unit as well if i remember correctly. I just didn't use the old thermostat. I was here with the guy during the wiring and installation. This happened when I tried the ecobee3 as well. Only on heat if I remember correctly
> 
> Sent from my SAMSUNG-SM-G935A using Tapatalk


Which thermostat did you have before the ecobee3? 

Does the fan come on without the nest on it's baseplate? 

Cheers!


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## chilleblanco36 (Dec 1, 2016)

supers05 said:


> Which thermostat did you have before the ecobee3?
> 
> Does the fan come on without the nest on it's baseplate?
> 
> Cheers!


It was a regular digital display thermostat. Nothing fancy. 

No, that's how I get the fan to stop running, by removing the Nest from its base. I left it off all last night. Put it back on and no fan until the heat comes back on. Just weird as I see a lot of people have this issue

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## chilleblanco36 (Dec 1, 2016)

If I can't get this figured out, I guess I'll simply return it and go back to my old simple to stat

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## supers05 (May 23, 2015)

"nothing fancy" isn't giving me enough information to help. I need a model number. Or, at least pictures of the wiring at the nest and the furnace. Nice and clear. I'm thinking that you have a line multiplexer device somewhere that's causing issues. (commonly known as an "add a wire" or "save a wire") You have to remove it. 

Cheers!


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## chilleblanco36 (Dec 1, 2016)

I'll try to get this today when I get home. Thanks 

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## carmusic (Oct 11, 2011)

humm thats like a triac output device trying to run a dc signal, it will latch once it is on and never unlatch
old thermostat was maybe with relay output so it didn't happen


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## supers05 (May 23, 2015)

carmusic said:


> humm thats like a triac output device trying to run a dc signal, it will latch once it is on and never unlatch
> old thermostat was maybe with relay output so it didn't happen


It's possible. I'm thinking it's more along the lines of working properly, and the old stat had something like a k terminal for signaling. However, it's only a theory at the moment. 

Cheers!


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## chilleblanco36 (Dec 1, 2016)

The old thermostat was never wired into the new system. The day I had the unit(whole system replaced) I went and bought the ecobee while he was finishing up the installment. 

I'm just now getting home. I didn't get here in time to pull the cover and get a pic of the wiring. I have the owner of the company coming out tomorrow morning to look at it to see if there is a wiring mismatch. I'll take pics when he pull it apart. 

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## chilleblanco36 (Dec 1, 2016)

Sorry for the delay guys. My A/C guy fixed it. He said the wires were incorrect at the air handler. Tested and the fan is off as it should be. Thanks again for your help. I'm a happy camper now 

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## Jasman419 (Dec 23, 2020)

I, too have the same problem. The original programmable thermostat (Emerson) had W, G, Y, Rh wires connected to their appropriate posts. Rh and Rc were jumped together on the old thermostat. I mirrored that wiring configuration on the Nest Generation 3 installation. The fan runs constantly though scheduling is off and the fan indicates it's not running. Running it for 15 minutes resulted in the fan not shutting off. I un-jumped the Rh and Rc connections - no change. Putting the Emerson programmable digital (model 1F78, max voltage up to 30V) back on resulted in proper fan operation. Down at the furnace I have nice green lights with the Emerson thermostat...with the Nest it's lit up like a (red) Christmas tree.


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## roughneck (Nov 28, 2014)

That’s the Nest causing it’s normal issues. It’s a terrible problem filled device. Your issues are related to the lack of a common wire, even though Nest will tell you it’s not needed.


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## Jasman419 (Dec 23, 2020)

roughneck said:


> That’s the Nest causing it’s normal issues. It’s a terrible problem filled device. Your issues are related to the lack of a common wire, even though Nest will tell you it’s not needed.


I may try and move the green to common, but I see in the thread that didn't work. I may also pay for Nest to come out to install it for $100...make it their problem. Thanks for the reply.


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## roughneck (Nov 28, 2014)

The issue is, their problem is a problem that keeps on giving. 
I’ve made a lot of money in service calls removing them.


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## user_12345a (Nov 23, 2014)

Jasman419 said:


> I may try and move the green to common, but I see in the thread that didn't work. I may also pay for Nest to come out to install it for $100...make it their problem. Thanks for the reply.


Don't waste more money on the nest tech, put the money towards a crow bar and sledge hammer to fix it.
Then put something decent on.

Ecobee or honeywell.


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## keithmauerman (Jan 4, 2021)

chilleblanco36 said:


> Hello all. I'm new to this forum. I just purchased a Nest thermostat. I like it, but I can't figure out why the dern fan constantly runs after the desired temp is reached. Called tech support and they verified it was wired correctly. Thought I had a faulty thermostat, but I got a new one and the same thing happens. This time I didn't even plug in the G wire and the problem still persists. I have a new Rheem 14 seer heat pump that was recently installed before the thermostat.
> 
> I have yellow for Y1, green for G, blue for O/B, red for rh, white for W1, and brown for common. Any recommendations? I really want to use this thermostat. Thanks in advance
> 
> ...


i had this problem and turned out the air filter just needed replacing once i did that fan quit running all the time


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