Wiring Nest with U1 wire

Reply

  #1  
Old 12-11-18, 03:57 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
Wiring Nest with U1 wire

I just bought two Nest learning thermostats for my new house, and am having problems installing the downstairs one. The thermostat replacement upstairs was fairly easy as I only had to match the wires. The downstairs unit has wires in the U1 terminal, and don't see a place for them in the nest thermostat. I went up in the attic, and traced the wire to where it goes. Pictures attached below



Thermostat Wiring

HVAC Control Board

U1 wire leading to this device
 
  #2  
Old 12-11-18, 04:33 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
That is a fresh air vent and the nest will not control it.
 
  #3  
Old 12-11-18, 05:28 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
What options do I have for this to work in some way?
 
  #4  
Old 12-11-18, 05:49 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
In order to come up with a work around..... you'd need to know how your old stat is controlling it.
In other words.... when does it open and for how long.
 
  #5  
Old 12-11-18, 07:08 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
Old thermostat died, so I can't see the settings. Hooked up my spare that came with the house. The vent open everytime the HVAC turns on
 
  #6  
Old 12-11-18, 08:02 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
Ok. In heat or A/C or both ? I don't know what climate you're in and how much fresh air you require.
It could be wired to open with the blower running or open when the heat is on.
 
  #7  
Old 12-11-18, 09:15 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
I live in Houston, so I we get a lot of humidity here. I went in the attic, and turned on Heat, and A/C individually which triggered the vent to open both times. It even turned on with just the fan on. What do the numbers on the actual fresh air damper mean?
 
  #8  
Old 12-11-18, 09:36 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
That's a Honeywell M847D-VENT "tru-zone" normally closed fresh air actuator.
The numbers refer to how far the damper opens. 3 = half way open.

M874D manual (pdf)
 
  #9  
Old 12-11-18, 09:39 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
It automatically went to 0 everytime, which is fully open if I'm right.
 
  #10  
Old 12-11-18, 09:43 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
Yes....... that is correct.
 
  #11  
Old 12-11-18, 10:04 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
So how do I go about wiring this?
 
  #12  
Old 12-11-18, 11:53 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
Post the part number off the control board.
 
  #13  
Old 12-12-18, 10:18 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
I couldn't locate the model number, but took many pics of tye actual board itself.

control board
 
  #14  
Old 12-12-18, 11:00 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
The board number is HK42FZ053 (CEPL131071-20)

If you connect the brown (vent) wire to the G terminal..... the vent will open when the blower is in FAN ON mode or A/C. If you put the brown wire on the W terminal..... the vent will open when the heat was on.

To have it open with heating and cooling...... you'd need a 120vAC relay or a 120vAC - 24vAC transformer. There is a terminal on the board called EAC. (electronic air cleaner). This terminal gets 120v whenever the blower runs.

Probably easiest to use a 24vAC transformer. Many places sell them.
24vac transformer.

The black connects to EAC 1 terminal. The white lead to neutral.
The two wires from the vent connect to the screw terminals.
 
  #15  
Old 12-13-18, 12:53 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
Would this transformer work? Transformer
 
  #16  
Old 12-13-18, 01:01 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
24vAC at 20va is fine. Your vent requires approx 8va.
 
  #17  
Old 12-13-18, 03:32 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
Which type of wire should I use to lengthen the wires on the transformer? Want to make sure I get the right type of wire/guage, so I don't cause issues.
 
  #18  
Old 12-13-18, 10:07 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
Normally 18-2 thermostat cable is used for wiring like that.
 
  #19  
Old 12-14-18, 10:49 AM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
Is there a way to install a timer? For example it opens twice a day for 20-30mins?
 
  #20  
Old 12-14-18, 11:17 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
Sure. You can use an Intermatic ST01 timer. It's electronic and runs for several years on its own internal battery. It could switch the vent directly. You can get 24vAC from the furnace or air handler.

Available in many home improvement stores and the like.
Intermatic ST01

Looking around on Ebay...... there are tons of timers. Here's one...
Timer
 
  #21  
Old 12-14-18, 12:12 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
  #22  
Old 12-14-18, 12:29 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
That timer needs and switches 120v. So if you were to use that..... you'd need a small 24vAC transformer that the timer would turn on.
 
  #23  
Old 12-14-18, 12:33 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
I got the transformer I posted about earlier would that work or are two transformers needed now?
 
  #24  
Old 12-14-18, 12:41 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
Sure.... that will work. Install the transformer on the side of a deep 4" square (1900) box and put the timer in a 1900 decora plate.

Name:  4 setup.jpg
Views: 2275
Size:  31.1 KB
 
  #25  
Old 12-14-18, 12:46 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
https://www.intermatic.com/en/timer-...ll-timers/st01 is this the same one you posted? Only you reason I ask because the model has a K after it.
 
  #26  
Old 12-14-18, 12:49 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
If that's the correct model above, can you give me the layout of the final wiring needed to complete this project? Hopefully I'll get everything in one final run to HomeDepot
 
  #27  
Old 12-14-18, 12:58 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
The K after stands for the three way timer. You only need single pole.

I posted the box and the plate. The transformer attaches to the box and the vent connects to the 24vAC terminals. The only additional thing needed is power to the box. You could use a power cord in the side of the box thru a connector.
 
  #28  
Old 12-14-18, 01:03 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
Guess the timer will still work since it allows for single and 3-way applications. Possible I can give you a call?
 
  #29  
Old 12-14-18, 04:38 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
Ended up picking up the timer you recommended, now need the wiring help lol
 
  #30  
Old 12-14-18, 04:50 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
Bring hot and neutral into the box.
Connect the neutral/white to the transformer white.
Connect the hot wire to one lead of the timer.
Connect the other lead of the timer to the black of the transformer.
Connect the damper to the 24vAC terminals on the face of the transformer.
 
  #31  
Old 12-14-18, 04:53 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
Where do I grab the neutral from?
 
  #32  
Old 12-14-18, 05:08 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
I don't know where power is around your furnace. If it's easier...... mount the transformer to the furnace or furnace safety switch and switch the 24vac leads instead of the 120v.
 
  #33  
Old 12-14-18, 05:21 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
Hot = EAC 1
Neutral = ?

Neutral ---- > Transformer White
Hot ----> Timer Lead
Transformer Black ----> Second Timer Lead
Damper Leads ----> Transformer 24vAC


Does that look correct?
 
  #34  
Old 12-14-18, 07:02 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
Oh....ok. You're going to have the furnace and the timer control the damper.
Looks correct. There are extra neutral connections on the main board. You can use any of them.
 
  #35  
Old 12-14-18, 07:46 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
Which way were you thinking of doing it? Do the ground from the timer, and thermostat just get grounded to the junction boz?
 
  #36  
Old 12-14-18, 08:02 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
Ground from the timer and transformer you mean...... get connected to the box.
 
  #37  
Old 12-14-18, 08:26 PM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
I cant find the extra neutral connections
 
  #38  
Old 12-14-18, 09:04 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
Check in the corner......
Name:  je5Ybpg.jpg
Views: 2245
Size:  41.3 KB
 
  #39  
Old 12-15-18, 12:02 AM
H
Member
Thread Starter
Join Date: Dec 2018
Posts: 21
Received 0 Votes on 0 Posts
Are all of those terminals in that section neutral?
 
  #40  
Old 12-15-18, 09:20 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 61,440
Received 1,411 Votes on 1,305 Posts
Yes..... they should be a lined box printed on the board.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: