Thermostat Cable

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Old 03-28-20, 11:06 AM
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Thermostat Cable

I'm trying to change my old thermostats to new wifi thermostats. Of course I have no existing C wire. I live in a very old house which has always made everything I've every attempted difficult. When I look at each of my 3 thermostats - the cables connected to them seem to go nowhere. When I look at the air handlers there is no similar cable connected. I looked at the boiler units and no evidence of similar cables running there. Typically where do the cables from the thermostat go? I assumed it should be the air handlers with the corresponding letters. I'm thinking that somewhere in the wall maybe the thermostat cable was spliced to a different cable but not sure that even makes sense by the look of things. Any thoughts/ideas? Thanks
 
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Old 03-28-20, 11:13 AM
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If the thermostat controls an A/C then the wiring goes to the air handler.
If the thermostat controls the heat then the wiring goes to the boiler.

Do you have zoned heat with zone valves ?
How many A/C systems do you have ?
 
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Old 03-28-20, 11:17 AM
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Thermostats control both AC and heat. I have 3 separate AC systems. I believe I do have zone valves. How would I confirm?
 
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Old 03-28-20, 11:25 AM
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If you have three complete A/C systems..... not A/C zoning..... then there would be a cable to each air handler.

Zone valves would be seen at the boiler.
Old houses would not have been wired for A/C and heat so someone at some time needed to run new cables for the A/C.
 
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Old 03-28-20, 11:43 AM
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So with no AC zoning would there still be zone valves at the boilers?
Apologize for being dense but are you saying that the cable at the thermostat is an old cable & that a separate new cable is connected at the air handler which must be spliced somewhere?
 
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Old 03-28-20, 11:56 AM
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If you have an old house..... it would have been wired for heat using multiple thermostats. Depending on the age..... more than likely the A/C wiring to the thermostat was added at a later late and the thermostats were upgraded from heat only to heat-A/C types.

You either have one circulator pump and zone valves or multiple pumps.

So you need to post how many cables at each thermostat.
What colors are on what terminals.
The wiring for the A/C should go to the air handler where another cable to the outside condenser is connected.

You have to investigate what you have..... I can only guess.
You need to know exactly what you have and how it's wired before considering wifi stats.

 
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Old 03-28-20, 12:19 PM
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Ok thanks. I will investigate further. I have two circulator pumps but only use one at a time. One acts as a spare.

When you ask about cables at the thermostat do you wires? there is only one cable to each thermostat.

Ex - One thermostat wiring - Red wire to R terminal then from there small Red wire to RH terminal
Orange wire to Y terminal
White wire to W terminal
Green Wire to G terminal
Spare Dark Blue wire wrapped around cable tucked into wall

Not sure this tells you anything


 
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Old 03-28-20, 12:38 PM
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Typically when a thermostat is upgraded from heat only to heat with A/C..... there would be a wire on R or Rc and a different wire on Rh.

As an example....... there would have originally been two wires. They would have been on R and W. When the stat was upgraded those two wires would now be on W and Rh. Then there would be wires on Y, G, and Rc. This would be considered a two transformer system. One in the A/C and the boiler one. Based on what you posted.... I don't see the heat and A/C being split. There are ways of doing it.

Keep digging.
 
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Old 03-28-20, 03:31 PM
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Here goes:

Ok - I was able to trace the cable to one of my thermostats to the air handler room. The cable from my thermostat is a white cable with 5 wires:
1. White Wire - W terminal on thermostat
2. Green Wire - G terminal on thermostat
3. Red Wire - R terminal on thermostat
4. Orange Wire - Y terminal on thermostat
5. Blue-Grayish Wire curled around cable not connected to thermostat

In Air Handler Room - I found White Thermostat Cable wires - spliced to brown cable wires as follows:
1. Green wire from thermostat cable TO Green wire of brown cable in air handler room - connected to G terminal on air handler
2. Red wire from thermostat cable TO Red wire of brown cable in air handler room - connected to R terminal on
air handler
3. White wire from thermostat cable TO White wire of brown cable in air-handler room - connected to a heavier gauge Blue Wire feeding box beneath switch box on air handler. NOTE: White wire does not connect to any terminal
4. Orange wire from thermostat cable TO Yellow wire of brown cable in air handler room - connected via pig tail to a separate black wire in a different brown cable (this brown cable only has two wires black and white) - the white wire from this same separate cable is connected to the B terminal on the air handler. Also connected to the same B terminal on this air handler is a thicker Gauge Blue wire going to that same box beneath the switch box on the air handler as the other heavy gauge Blue Wire pigtailed to the white wire. So essentially two thick Blue wires going to this box.
5. Unused Blue-Grayish wire from thermostat cable - connected to Blue wire of brown cable in air handler room - NOT connected to anything/terminal on other end.

Terminal Plate on outside of Air Handler does NOT have a C terminal.
The terminals I see are:
R - has Red wire on it
O - nothing on it
B/C - has white wire from separate two wire cable on it and Heavy Gauge Blue Wire
W1 - nothing on it
W2 - nothing on it
Y- nothing on it
G - has Green wire on it
T - nothing on it

So it would "seem" like if I had a C terminal on this plate on the air handler I could simply connect the end of the Blue wire to it and that would work but I don't see a C terminal. Could another lettered terminal represent the C terminal?

Not sure about the heavy gauge blue wires - supplying the small box under the blower switch box - I assume they control the blower??? When I shut the switch above that bix the air handler goes quiet

Sorry for the long winded post but I wanted to give you as much detail as I could.
 
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Old 03-28-20, 03:48 PM
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Ok.... let me help clarify. I'm guessing you have Trane A/C equipment. Trane uses B as the C connection. I changed your list to show B/C. That is the C connection.

The two wire cable goes to the outside condenser. It will connect to B/C (white wire) and then to the Y thermostat connection which mean orange to black of two wire cable.

I'm trying to figure out what the brown wire is for at the air handler.
The white five wire comes from the stat. ]
The two wire goes to the condenser.

3. White wire from thermostat cable TO White wire of brown cable in air-handler room - connected to a heavier gauge Blue Wire feeding box beneath switch box on air handler. NOTE: White wire does not connect to any terminal
We need to see what this box is. If we are lucky it's a relay that controls the heating zone.
 
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Old 03-28-20, 04:03 PM
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I've attached two photos:

1. One Shows the wiring to the terminal plate
2. The other shows the box underneath the switch box that is fed by the two heavier gauge Blue Wires

The other Brown 5 wire cable you ask about is essentially just a continuation of the White 5 wire cable from the thermostat
 
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Old 03-28-20, 04:10 PM
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That looks like a RIB relay and is installed in that electrical box. It looks to be activated by the thermostat via the B/C and W wires. We need to find out how that controls the boiler.

You've made some good progress. The next step would be to shut down power to that electrical box with the relay and find out what the relay is connected to. It may supply switched 120v to a circulator pump. Kind of a lame way of doing it but it is possible.
 
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Old 03-28-20, 04:34 PM
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I've attached some more photos that are brighter & clearer. Maybe it will help
One is of the splicing of the thermostat cable to that other brown cable I spoke of.

If the B terminal serves as a C terminal why could I not just hook up the unused wire to that?
 
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Old 03-28-20, 04:40 PM
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Yes.... you can connect the unused wire to B/C.

I see what they are doing. The two blue wires are the 24v control for that relay. The two red wires coming out of that junction box are from the relay and connect to a two wire brown cable. That is the heating line to the boiler.

So someone has already done the setup work for your new stat.
 
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Old 03-28-20, 04:59 PM
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So just to confirm:

1.I can take that unused Blue-Gray wire at the thermostat (in the white cable) and connect it to the C on my new Wifi Thermostat.
2. At the air-handler end I can attach the unused other end of the Blue Wire (from the spliced white to brown cable) to that B terminal - sharing that B terminal with the white wire to the condenser & one of the heavy gauge Blue wires for the 24v control.

That should work?

Is there any issue with the way they tape spliced the white thermostat cable to the brown cable? They only twisted & taped those low voltage wires. Now that I'm using that blue wire - which is ultimately connected to that 24v control via the shared B terminal is there any fire risk? Should I redo the splice using wire nuts & tape?
 
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Old 03-28-20, 05:05 PM
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No need for tape. Just use wire nuts.
 
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Old 03-28-20, 05:09 PM
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Do I even need to bother undoing the tape & using wire nuts or could I just leave the tape?

Any fire risk?
 
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Old 03-28-20, 05:13 PM
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No fire risk but it's reassuring to know the connections are solid.
 
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Old 03-28-20, 05:17 PM
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Thank you for all the help.

I'll give it a try and let you know
 
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Old 03-29-20, 02:16 PM
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So I did as we discussed & happy to say it worked!

Tried my other two thermostats - problem I have with those is the cables from the thermostats were also spliced to another cable which ends at the air handlers however they must have spliced them & buried the splice in the walls somewhere. When I test any spare wires they are not continuous between the thermostat & air handler (like the one I was able to upgrade). Looks like I may have to choice but to try and run an extra cable somehow
 
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Old 03-29-20, 03:34 PM
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Good luck. Keep me updated as to your progress.
 
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Old 03-31-20, 07:38 AM
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So the thermostat which I installed seemed to be working properly initially but now I've noticed a new issue - the fan seems to run continuously whether the unit is off or set to heat or cool. I did some googling and they mentioned a shorted thermostat wire as a possible cause. Not sure if I accidentally did something. Odd that it seemed to be working fine initially and now this. Any thoughts?
 
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Old 03-31-20, 08:52 AM
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One additional bit if information. Don't know if it provides any useful information to helping diagnose what the issue with the fan is.
I shut the switch controlling the fan because I didn't need it to run continuously

When I shut this switch - above that 24V control - it shuts the blower/fan & the thermostat goes dark. I guess this makes sense because the 24V control is supplied by the two heavier gauge blue wires one of which shares the B terminal with the C wire on the new thermostat. So I guess the power supplied to the 24V controller is also providing the power to my new Wifi Thermostat?

Does this imply some kind of shorted thermostat wire or that I can't use the B terminal as my C terminal?
Now I'm not sure if the fan was working properly as I originally stated. Maybe I just I assumed it was.
 
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Old 03-31-20, 10:14 AM
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The G terminal is blower control.
Try disconnecting the G wire at the air handler and see if blower stops.
 
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Old 03-31-20, 10:35 AM
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Should I disconnect the G wire while the unit is running? or do I shut the fuse to the air-handler first & then do it?
 
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Old 03-31-20, 10:41 AM
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Probably shut off the power to eliminate a short.
 
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Old 03-31-20, 10:43 AM
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Ok. I'll do that. What will that tell me?
 
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Old 03-31-20, 01:01 PM
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So I disconnected the Green Wire at the air handler and the fan still runs
 
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Old 03-31-20, 01:03 PM
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Ok..... then the problem is inside the air handler. The G terminal supplies 24v to a relay inside of the air handler. Post the model number for your air handler.
 
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Old 03-31-20, 01:15 PM
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So I've attached a photo of my air handler model number.
Looks like: TWH036B140A1

On a side note - if I reconnected my old thermostat and didn't hook up the c wire to it and the fan works correctly would that tell us anything?
 
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Old 03-31-20, 02:54 PM
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So I reconnected my old thermostat the way it was. Removed my C wire from the B terminal as well. The fan still runs continuously regardless of whether the system is on or off, heat or cool. I'm pretty sure it wasn't that way before. Any ideas?
 
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Old 03-31-20, 03:07 PM
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Looking at the decal for the air handler. The grid (BAY) is for electric heat.
Is there a check or a mark in the first column for any of those electric heat options ?

There is just a basic switch to shut down the air handler...... not a large breaker.... correct ?
 
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Old 03-31-20, 03:52 PM
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There is no check mark next to any of the BAY options.

Yes the basic switch (which you may have seen in some of my earlier photos above the 24v control supplied by those two heavier gauge blue wires) shuts down the air handler i.e fan goes off - independent of the large breaker.

Separately I managed to find a splice to one of my other thermostats but I'm holding off on changing it until we sort this out. I don't want to make the same connections and cause any issues
 
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Old 04-01-20, 04:25 PM
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Hi Pjmax

Kind of in limbo right now. Any follow up thoughts regarding the fan issue?

Thanks
 
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Old 04-01-20, 04:54 PM
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There should be something..... little board.... relay attached to the G wire inside the air handler. See if you can get a picture of the inside. I'm not able to find the manual for that air handler. I'm assuming it uses a fan relay or time delay board that may be bad. Doubtful you caused any problems..... they just go bad.
 
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Old 04-02-20, 06:14 PM
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Hi PJmax

I managed to take some photos inside the air handler - You can see a green wire arising from the inside of that G terminal and follow it to the fan unit.
The last two photos are outside of the Air handler showing that switch.

I don't know if this shows you what you need to help me figure this out. Thanks
 
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Old 04-02-20, 06:32 PM
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Here's what we are looking for. There should be a relay inside that box.

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Old 04-02-20, 07:50 PM
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Ok so here is the inside.
When I gently touched the green wire it disconnected from the circuit board. Fortunately I was able to find the two holes on the circuit board and reattach it. It works the same way as it did before i.e the fan always runs unless I shut the switch or the breaker. Do you think the connection at the circuit board could be the issue? I wouldn't think it would run continuously in that case but almost would expect it to not run reliably.
 
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Old 04-03-20, 09:35 AM
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I believe I found the replacement part for this Heat Pump Relay - Do you think that is likely my issue?
Would you recommend replacing it?

Do you think there is anyway my wiring the new thermostat could have caused this issue? reason I ask is I'd like to try to rewire another one of my thermostats the same way - Do you think connecting the hew thermostat wire to that B terminal might have caused a short or something?
 
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Old 04-03-20, 10:01 AM
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Relays don't normally stay engaged by themselves unless the contacts are burned or arced together. That looks like a timer or delay relay board. Pretty intricate relay for blower control. There must be a problem in the electronic delay part of the relay and keeping it engaged.
 
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