Welcome to the DoItYourself Forums!

To post questions, help other DIYers and reduce advertising (like the one on your left), join our DIY community. It's free!

Installing Ecobee4 but lack a C wire


Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-08-18, 06:26 PM   #1  
Installing Ecobee4 but lack a C wire

Hi Guys, I thought I'd continue an existing thread rather than starting a new one. (Please let me know if that's not the best approach).

I have an existing 2 wire unit that I am trying to install an Ecobee4 to control. I have done some reading/research through this forum and the Ecobee support section and I am still confused as to the exact approach I should take.

My existing control board for my heater is below:
B9ey41cCRlr1TmY3ZDA1aUJFOFlkcy1aeUEycUZNc21FYWNn
Name:  e1.jpg
Views: 325
Size:  92.2 KB

ey41cCRlr1MUh3UkFSM1FOWUZEZjBEaDI5N2ZMdmR4WG1r
Name:  e2.jpg
Views: 334
Size:  51.4 KB

And my existing heather thermostat is:
ey41cCRlr1OUZGaDFWaXM3X3U1blFpcDB2Q3dBU2dRLU9r
Name:  e3.jpg
Views: 325
Size:  49.5 KB

From what I can gather, I needs to purchase a "FAST-STAT common maker and sender" to create the 3 wires (R,W & C) I need to make the Ecobee4 work, using my existing 2 wires on the control board (marked 'T/Stat'). I have been doing some reading from this link - https://support.ecobee.com/hc/en-us/...-installations

Just wondering if this is the best approach or not?

The other issue is actually being able to buy the FAST-STAT equipment as Amazon appears to have none in stock or an indication of when it will be back in stock.

Appreciate any help you guys can give me on this!

Thanks,
Dane

Mod note: member from Australia


Last edited by PJmax; 01-08-18 at 06:48 PM. Reason: added pics from links
 
Sponsored Links
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-08-18, 06:57 PM   #2  
Welcome to the forums.

I'll be moving this to its own thread. Your system is nothing like the one in this thread.

You have a data type communicating system. That thermostat tells your heating (cooling ??) what to do based on digital commands. I don't recognize the control board used there and cannot tell you how to bypass it. The Fenwal unit is just for the furnace ignition. The control board tells that when to fire and when to activate the blower. I'd need to see the service manual for that furnace or a wiring diagram but based on what i see in the pictures..... no Ecobee for you.


~ Pete ~

 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-08-18, 07:06 PM   #3  
Thanks for that Pete, I'm not 100% on the exact model, but it should be covered in this - https://www.energyaustralia.com.au/r...n%20Manual.pdf

I'll take some more photos this afternoon and post them up.

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-08-18, 07:16 PM   #4  
I looked over the manual. No real wiring diagrams in there but it looks like that control board is integral to the operation of that unit. I don't think you can run the system without it.

Is this just heat or heating and cooling ?


~ Pete ~

 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-08-18, 07:22 PM   #5  
The is a central heating unit only. No cooling.

If I connect the 2 wires together that were wired into the existing thermostat, the heather turns one until the wires are pulled apart.

I assumed (stupidly obviously) that a smart controller would be able to manage this, but it looks like I am wrong...

Probably should have researched better before buying!

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-08-18, 07:25 PM   #6  
You could power the ignition board from the ecobee but the blower is controlled by that SCC board. No easy easy way to have the ecobee control the blower. There is also a sensor inside the duct that reports back to the SCC board. The ecobee can't use it.


~ Pete ~

 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-08-18, 07:59 PM   #7  
Well that sucks, I assume any of these methods would result in the Ecobee having power and being able to switch the ignition board. But the blower would never turn on?
https://www.fast-stat.net/pdf/Common...ctions-Set.pdf

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-08-18, 08:22 PM   #8  
Do you know any people down there in the HVAC trade ?
They may be able to help you.

I've never worked with that unit you have.


~ Pete ~

 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-08-18, 08:25 PM   #9  
unfortunately not. I might try and find a great forum like this that is Australian based. Hopefully someone here might have done something similar already!

Thanks for your help so far, much appreciated!

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-08-18, 08:38 PM   #10  
If you can find more technical info on that unit..... especially servicing.... let me know.


~ Pete ~

 
doughess's Avatar
Member

Join Date: Apr 2014
Posts: 372
NY

01-09-18, 06:39 AM   #11  
On the circuit board to the right of the green Earth dot is a white box marked 24 volt transformer. Those wires go transformer partially visible in the upper right corner of picture. One of the two black wires in that box is C.

Use a volt meter and measure from one black wire to the thermostat wires. One of the 2 will read 24 volts. That is C wire.

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-09-18, 09:43 AM   #12  
Doug got me thinking. When I look closer at your stat I see it's connected to Rh and W. That means that it is not a communicating thermostat. The part that needs to be checked into is that there are two brown wires on the thermostat but not at the control board. Do you know why ?

Looks like gray at the board.


~ Pete ~

 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-09-18, 04:17 PM   #13  
Hi doughess - you are correct, there is a 24VAC transformer just out of the picture. I assume I just find the 24V, use this as the common and then the normal R and W wires that the old thermostat used? Then this should suffice the Ecobee?

PJMax - I ran new wiring to the circuit board as I have moved the thermostat location and could not pull back the old brown wiring. I went to connect it all up (new grey wiring) and realised during this process I needed to get some help. Sorry for the confusion!

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-09-18, 04:27 PM   #14  
Are you going to pull a third wire to the stat for C ? It would simplify things.

In the picture below...... you don't know whether A or B is W or R. You will need to determine that. If you run a third wire to the stat..... it can be done there. You need to use a voltmeter set to AC voltage to read 24vac. You need to check from A to C or B to C. One will show 24vac. Mark that terminal with an R. The other terminal is W.

Name:  e1.jpg
Views: 301
Size:  41.5 KB


~ Pete ~


Last edited by PJmax; 01-09-18 at 05:03 PM.
 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-09-18, 04:55 PM   #15  
Yes, I can pull the second set of grey wires from the "24V Refrig Output" as they run to the new location for the thermostat. I initially thought this was labelled "24V output" before cleaned away the dust, hence I thought I could pull the common from there.

I have a further question sorry! But these 2 black wires are the wires that come out from the low voltage side of the transformer
https://drive.google.com/open?id=1fM...uX7Z1N-0XseSR4
(I am not 100% on where the black ground/earth wire comes from)

Are you certain that the wire you marked C is still the common to use?

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-09-18, 05:05 PM   #16  
How dare you question me.

Yes..... I incorrectly marked my picture. The correct terminal has been marked.
Good catch.


~ Pete ~

 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-09-18, 05:43 PM   #17  
Now I think you have given me more credit than I deserve, now I am even more confused! I was expecting the'C' to be either X or Y marked below. But are you saying it is Z?
https://drive.google.com/open?id=1JD...eqVj7xEm9UdVQn

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-09-18, 05:48 PM   #18  
I added a pink circle to the diagram. Aren't these the two secondary wires from the transformer ?
That long black one you have circled looks like a primary lead to high voltage.

Name:  Capture.JPG
Views: 284
Size:  21.2 KB


~ Pete ~

 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-09-18, 05:51 PM   #19  
The 2 black wires I circled are exiting the low voltage side of the transformer. The pink wire you circled I cannot remember where that comes from.

From memory, there were only 2 black wires leaving the transformer, both of them are what I circled in red.

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-09-18, 06:10 PM   #20  
You need to double check. It would make sense the two I circled where the secondary. The black wire you circled connects to the blue/neutral buss area of the board. That should not be a low voltage connection point.


~ Pete ~

 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-10-18, 02:58 AM   #21  
I am sorry PJmax, you were correct with your black wire assumption, the 2 black wires next to each other are in fact the low voltage from the transformer.

I did some checking of voltages with a multi meter:
A to B = 27V
A to C = 27V
A to D = 0V
B to C = 0V
B to D = 27V
C to D = 27V
Referencing the image in the below (plus the link if the attachment doesn't work):
https://drive.google.com/open?id=12t...2VsYOBn1SWkwYJ

I also have an image of the wiring diagram from the underside of the heater cover if it's useful:
https://drive.google.com/open?id=1Ne...p5D8B2YwJZLf6r

Attached Images
     
 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-10-18, 11:22 AM   #22  
So A is the R terminal and B is the W connection.
Just to verify...... R to C =24v and W to C = 0v.

Name:  e1.jpg
Views: 65
Size:  39.5 KB


~ Pete ~


Last edited by PJmax; 01-15-18 at 08:29 PM. Reason: corrected diagram
 
doughess's Avatar
Member

Join Date: Apr 2014
Posts: 372
NY

01-10-18, 12:33 PM   #23  
Pjmax
“Doug got me thinking. When I look closer at your stat I see it's connected to Rh and W. That means that it is not a communicating thermostat. “

On low voltage thermostats terminals Rh and W when connected together start the burner, or whatever. They have no significance or implication to whether thermostat “communicates” via wifi, bluetooth or IR.

 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-10-18, 02:06 PM   #24  
thanks for all of your help guys!

Will try and connect it all up tonight.

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-10-18, 02:09 PM   #25  
@doug...

I didn't see that the wires were on R and W at the stat until I enlarged that part of the picture. That basic stat connection was not shown in the manual.


~ Pete ~

 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-11-18, 02:11 AM   #26  
So I wired it up as suggested and the unit will not power on.

I have 27v between r and C and 0v between W and c.

But no powering up!

Any thoughts?

 
doughess's Avatar
Member

Join Date: Apr 2014
Posts: 372
NY

01-11-18, 07:31 AM   #27  
Go back to where those wires come from and measure there. Another way is to take thermostat there and temporarily connect it.

Older thermostats had one letter terminals: R W G O Y, etc.

R is one side of 24 volts. C is other side of 24 VAC transformer but was not on most older ones. Separate Rh and Rc terminals are used to avoid issues.

Newer thermostats use Rh for heating and Rc for air conditioner. Heating and AC units may use separate 24 VAC transformers that if interconnected could cause problems.

Old Honeywell clock thermostats actually had two 24 VAC transformers, one just for clock.


Last edited by doughess; 01-11-18 at 07:46 AM.
 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-11-18, 11:22 AM   #28  
Hi Doug,

Exactly the same voltage meausured at the control board and the thermostat still does not work when connected at the control board.

I tried running new thicker guage wire for this and still no love.

I also connected R & W up to make the heater run and the ecobee still didn't turn on.

Thoughts?


Last edited by Dane_Aus; 01-11-18 at 11:48 AM.
 
doughess's Avatar
Member

Join Date: Apr 2014
Posts: 372
NY

01-11-18, 04:32 PM   #29  
verify that there is 24 VAC between the C and R terminals. If 24 VAC then problem is in Nest.
I would never buy a Nest so can help with hands on experience.


Last edited by doughess; 01-11-18 at 06:05 PM.
 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-11-18, 07:47 PM   #30  
Doug.... this is an Ecobee 4.

Not sure if it's a new one but..... if there is 24vac on the Rc and C terminals..... the stat should work. You should be using C, Rc and W1 on the ecobee 4.

I will be moving this thread to the "thermostat" forum tomorrow.
I didn't even realize it's the boiler area.


~ Pete ~

 
Dane_Aus's Avatar
Member

Join Date: Jan 2018
Posts: 18

01-11-18, 09:05 PM   #31  
Hi Pete, brand new from Amazon.

I have tried it wired:
- Rc, C & W1
- Rc, C & W2
- Rh, C & W1
- Rh, C & W2

None work.

The only other thought I had was to connect the other low voltage wire out of the transformer to Rc, +24V from transformer to C, R to Rh and W to W1 and see if this powers up the unit.

Sorry about the thread location, I just followed a similar ecobee question as I thought it wouldn't need it's own thread. Apologies if that wasn't the correct way to go about it.

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-11-18, 09:21 PM   #32  
You could try both transformer leads right at the control board to C and Rc to see if the stat powers up.


~ Pete ~

 
doughess's Avatar
Member

Join Date: Apr 2014
Posts: 372
NY

01-12-18, 06:14 AM   #33  
Some thermostats use Rh for heating and Rc for air conditioner. Heating and AC units may use separate 24 VAC transformers that if interconnected could cause problems. Thermostat should work with wire to either.

Dane_Aus should be aware of the different functions of Rc and Rh. On systems with a single "R" wire for both heating and cooling Rc and Rh are jumper-ed or there may be a setup option to operate either way.

 
zoesdad's Avatar
Member

Join Date: Jan 2008
Posts: 2,511
PA

01-12-18, 10:42 AM   #34  
This is probably a nave question but how are you physically connecting the new C wire from the ecobee to the control board? I may have missed it in the pictures, but I did look.

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-12-18, 10:53 AM   #35  
Basically C is ground so the wire can connect to a ground screw on the control chassis.

As mentioned previously.... this is an Ecobee 4 stat and does not want the R's combined. Their wiring diagram illustrate using the Rc terminal for single R wire connection.

Actually what we need to know is if the 24vac is measured on Rc and C with the stat actually connected. If yes..... the stat is at fault.


~ Pete ~

 
doughess's Avatar
Member

Join Date: Apr 2014
Posts: 372
NY

01-12-18, 07:53 PM   #36  
************************************

 
doughess's Avatar
Member

Join Date: Apr 2014
Posts: 372
NY

01-12-18, 07:56 PM   #37  
Pjmax
Basically C is ground so the wire can connect to a ground screw on the control chassis.

Wrong. C should never be connected to earth ground on metal frames or whatever. C should not be considered as ground. C stands for "common". Within the 24 VAC control circuits C is the common side of power for various items.

A basic concept for ungrounded C is to isolate 24 VAC circuits from 120 VAC power in case there was accidental contact with AC hot. This way if 120 VAC hot makes contact with either side of electrically isolated 24 VAC nothing should be harmed. But then there is always Murphy's Law which in case might literally spark a house fire.


Last edited by doughess; 01-12-18 at 09:03 PM.
 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-12-18, 08:34 PM   #38  
Are you following this thread. Let me call your attention to this picture where one of the secondary transformer leads is connected directly to ground.

Name:  e1.jpg
Views: 121
Size:  39.2 KB


~ Pete ~

 
zoesdad's Avatar
Member

Join Date: Jan 2008
Posts: 2,511
PA

01-13-18, 09:26 AM   #39  
If you blow up this diagram -

https://drive.google.com/file/d/1Ney...2YwJZLf6r/view

on the left side it definitely shows one lead of the secondary on the transformer going to earth ground, and the green-yellow wire (marked blue C in post #38) also going to earth ground. That matches the posted pictures.

But I find it curious that Dane never asked, or it never came up, precisely at which point the new C wire should be connected and how to do it. Do you need a new connector, etc.? Those are questions I would have had but I dont mess with this stuff much and Dane may be way ahead of me there.

Will the ecobee actually power up with just Rc and C connected? I wonder if it will refuse to power up if W1 isnt also connected. You would think Rc and C would be enough but it seems to me the manual section for Troubleshooting Power-ON problems is vague.

 
PJmax's Avatar
Group Moderator

Join Date: Oct 2012
Posts: 42,486
NJ

01-13-18, 09:31 AM   #40  
At the risk of being repetitive,,,, if there is 24vac on Rc and C at the stat... it should come on. It doesn't need any other wire connected.


~ Pete ~

 
Search this Thread