Hello everyone! Got a problem where I'm trying to install my 3rd Generation Nest Thermostat for my Air Conditioner and Gas-Powered furnace, but I have an EARD Fresh Air Damper wire in the U1 position that I don't know what to do with (see attachment).

I've contacted Nest Support, but was told to either put it in the * section, or to just cap it off completely and don't worry about it. Considering we have a gas-powered furnace that likely needs fresh air to function, plus we live in North Texas (read: hot), I didn't think the latter option was viable, and the former option doesn't sound right since there's no functionality for a Fresh Air Damper in the Nest Thermostat.

Thanks in advance for any and all help--kind of stuck on this one.

 

Nest doesn't know how to control a fresh air damper. Look at the programming for how your current system is set up. Then might be able to come up with a work-around.

 

Welcome to the forums.

The typical setup is on a call for heat......the damper opens.... then the burner starts.
This is a fail safe method as the damper must be open for the burner to start.

If the damper is to allow an extra bit of fresh air in you could connect it to the heat line of the thermostat so the burner and the damper are activated at the same time.

 

 

As far as I know..... U1 is a programmable switch. On or off.

 

Ah, so the damper is only in an open/close state, and likely only open when the heating is triggered? That's good to know...

 

The Nest is a pretty thermostat but your existing thermostat ia a better thermostat.

I am not sure why you believe that a fresh air damper is required for heat mode but the Honeywell gives you the option of running fresh air 20% of run time.

With today's tighter homes fresh air ducts are more popular to help prevent the house from going into negative pressure when you run any exhaust fan.

An internet gateway can be added to the Honeywell Redlink thermostat.

 

I have a feeling the gas furnace is in an air starved location and the fresh air vent was added to open when the furnace is running for additional combustion air.

 

 

If the fresh air is controlled by the thermostat ( I have never seen this done), I recommend rewiring to the W circuit ( I have done this).

I am not a fan of Nest thermostats. I have installed quite a few of them but I don't like the star terminal setup or the programming of them.

 

Hey, I'm pretty much in the same situation but down here in Houston. I've got a fresh air damper (normally closed) wired to the U1 on my TH8321 Honeywell thermostat and it's set to run 20% so it's opening up every now and then with the AC system (cooling since we're in summer). How did you end up setting this up? I was thinking of leaving the vent open all the time, which I don't know if it's a good idea to do that in such a humid environment. Is there anyway I could wire this so the vent opens whenever cooling or heating is running?

 

Victor a combustion air damper and a fresh air damper serve different functions.
A combustion air damper should be open any time the heat runs and it feels the fire oxygen. This is not for the conditioned space

A fresh air damper is to help prevent the house from going into negative pressure when you run exhaust fans. This is for the conditioned space.

If a fresh air damper is always open you are more likely to grow mold in the duct work.

A Honeywell thermostat can be configured to only open the damper a percentage of the run time.

If it is a Honeywell Redlink thermostat you can add a wireless outdoor sensor that can lock out fresh air when the humidity is high.

A Nest cannot control a fresh air damper in this manner.

 

Bunji your current setup is better.

Have you tried entering setup to view your damper options?
Do you have a TH8321U or a TH8321R or a TH8321WF ?

The TH8321R is the Redlink model that accepts the OA humidity sensor.

 

Hey Houston204,

The model is TH8321WF1001. I checked the damper options. It's set up for Fresh air damper with percent on time of 20%, and there are no outdoor conditions (I don't have any outdoor sensors). I don't have a humidifier, and dehumidifier is just the A/C. The ventilation options are just Mode (off/auto/on), temporary boost, and lockout. I went up and looked and the U1 wire is connected to a AprilAire damper, and the attached vent goes from supply side to outside. If I'm understanding correctly, and based on what I've observed by checking equipment status while AC is on, its just a damper that opens randomly 20% of the time when the blower is operating so that it draws in some fresh outside air. I do need to try and see if the blower turns on when I turn on ventilation, haven't tested it yet.

The main reason I wanted to change the t-stat is I have some other Nest equipment in the house and I can keep it all on one app. I've also found that the master bedroom gets way colder than everywhere else and I wanted to add a temp sensor in the room to connect to a Nest Thermostat so that at night it tracks the bedroom temp instead of the hallway.

I also noticed I don't have a wire in the g terminal on the thermostat even though I have the option to run the fan only. This is a new build, so is that just the sub-contractors being too cheap/lazy to pull higher conductor count wire, or is it a straight up mistake on their end for not pulling the correct wire count to sufficiently wire the thermostat to controller, HZ311 (not sure if there's any standards or requirements in HVAC world regarding fan operation).

 

If you found a remote sensor for a Nest thermostat can you post a link?

I know that Honeywell offers them but to my knowledge Nest does not offer a remote temperature sensor for their thermostat.

 

Nest recently started offering the remote sensors. Doesn't work with the older 1st or 2nd gen thermostats, though.
https://nest.com/thermostats/nest-te...nsor/overview/

 

Houston, sorry for the delay in getting back to you--new house move-in drama kept me away, and now I have time to tackle this again.

It's a fresh air damper for my AC/Gas Heater unit in the attic for our new home. The reason I have a Nest is because I'm in the ecosystem for the alarm, camera, and doorbell offerings and our builder put our thermostat in the master bedroom...which wasn't very smart IMO. We need to keep the master bedroom door shut (kids, puppy), so we need something that can handle multiple remote sensors (hence, the Nest 3G).

I went up and looked at the HVAC unit in the attic, and I couldn't see where the U1 cable came from. I did see the manual switch on the side where the fresh air damper is, so I don't know if that just controls the opening size when it does turn on, or it overrides whatever automatic settings are there.

So is it possible to take the Fresh Air damper wire and get a separate box to control it? Or since the U1 is just an on/off for the fresh air damper, would using the * connector on the Nest suffice, since it just needs to know if the HVAC is running or not?

Inquiring mind wants to know.

 

I see this thread was going around in circles. What needs to be decided is if you need makeup air for the gas furnace or you just want fresh air allowed in at certain times. In my opinion... I can't see why you'd need any type of fresh air vent in an attic. The duct work should be 100% sealed from the attic air. You need to decide what you want the vent to do and then the wiring can be established.

 

 

I am in the same boat (Houston as well). I have two extra wires that I don't know what to do with. I traced the wires and I am pretty sure one of the wires goes to this outside my house....



So did you ever find a solution?

 

I have a very similar issue. A black wire connected to U1. I'm not to versed in hvac systems but it seems to be connected to a damper (normally closed).

Did you ever get a solution???

 

The nest will not control it. You need to decide what you want the vent to do.
Do you want it open when the heat is running ?
Do you want it open for 1 hour every day ?

You're disconnecting it from a controller that was specifically designed to run it.
Now something needs to be designed to do what you want.

 

You can install nest by installing a ventilation control separately and changing some wiring in HVAC system then you don't need to connect U1 in nest. Whatever you had programmed in your honeywell thermostat, you can program in your new controller. Some compatible controllers are honeywell W8150A100A, Jackson system IP-FAVPAN etc. You need a 24VAC transformer as well.

 

Thanks for the additional information but the member wanted to control it with the nest... not a separate controller. Since that was a year ago.... I'm sure he has worked out a solution.