Trane to Honeywell tstat with unusual wiring.

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Old 01-06-15, 08:04 PM
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Trane to Honeywell tstat with unusual wiring.

Hi folks,
So I unsuccessfully pored through the forums for this wiring help even though it seems like there are a zillion post on Trane/Honeywell.

I'm upgrading my TCONT802 to the RTH9580WF because most of the screen stopped responding and now I can use a fancy wifi model. It is a 3H/2C two stage heat pump.

Current wiring is this:

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Y2 - brown
X2 - blue
W1/W2 - white
RC/R - red
W1/O - orange
Y - yellow
G - green

So, the issue seems to be my common wire. At the furnace, I have:

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G - green
B - blue
R - red
O - orange but jumpered to R
W1/W2/W3 - white
BK - brown
Y - yellow

Based on other comments I've read, Trane uses B for common but I don't think that works with X2. I'm thinking it's orange (plus, I tried blue and the unit doesn't power up. It powers up with orange though). I'm somewhat confident in the following on the new unit:

C - orange
R/RC - red
W-O/B - white
Y - y
G - g
W2-Aux/E - blue
Y2 - brown

Does this seem right?
 

Last edited by PJmax; 01-06-15 at 09:35 PM. Reason: repaired pic
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Old 01-06-15, 08:26 PM
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Welcome to the forum! To better assist, can you post the model number of your air handler and heat pump so wiring can be verified?

I'm somewhat confident in the following on the new unit:

C - orange
R/RC - red
W-O/B - white
Y - y
G - g
W2-Aux/E - blue
Y2 - brown

Does this seem right?

The wiring you propose for the new stat is partially incorrect.

The orange wire needs to go the O terminal on the new stat
The white wire need to go to the W2/Aux-E terminal on new stat

You are correct that Trane uses B as the common terminal. In the photo, it appears you have a blue wire going to X2. The blue wire going to the B terminal at the air handler should be going out to the heat pump condenser. To get a C (common wire) for the new thermostat you will need a wire from the B terminal in the air handler to the C terminal on the RTH9580WF. The X2 wire at the air handler will go to W2/Aux-E terminal on new stat.

Do you have an unused wire at the air handler and thermostat?
 

Last edited by firedawgsatx; 01-06-15 at 09:08 PM.
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Old 01-06-15, 09:03 PM
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Thanks! So the models are Trane air handler 4TEE3F37B1000A and Trane heat pump 4TWX6. Yes, I'm perplexed on the blue wire (and the orange). I can confirm that connecting the blue wire to C will not power the new tstat. There is no orange wire coming from air handler terminal (just the jumper to R) so I'm not really sure where the orange wire originates. And there is no unused wire at either the air handler terminal (that I can see) or tstat.

I hooked up the wiring as I outlined earlier and it (initially) looks like things are working but now the RTH9580WF loses power and I've already had to cycle the circuit breaker twice to bring it back on line. My confidence is waning. Would the tstat power up with anything other than the common? Can I disconnect all but the R/RC and try out the C terminal with other wires?
 
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Old 01-06-15, 09:21 PM
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Now that you have provided the model numbers I can review the wiring and see how to configure the wiring.

The orange wire goes to the reversing valve at the heat pump. Do you have an orange wire coming from the heat pump to the air handler?

The blue wire at the air handler on B terminal should be going outside to the condenser. Normally, to power the C terminal on the new stat you would need another wire from the B terminal at air handler to the C terminal on the new stat. But, since you don't have an extra wire at the stat or the air handler you have two options: run another wire to the thermostat or use the G wire as the C wire.

I'll review the wiring and get back with the solution.
 
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Old 01-06-15, 09:59 PM
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We are going to need several more photos of the thermostat wiring bundles in the air handler.

The wiring in your air handler does not make complete sense to me. At the air handler you should normally have two wires on the Y terminal, the R terminal, W1 and the BK terminals. The orange wire can go directly from the O terminal on the thermostat to the O wire at the condenser but is most often connected at the O terminal.

Here is a link to the installation manual for your heat pump. It has several wiring diagrams for reference.

http://www.bayareaservice.com/wp-con...stallation.pdf

The wiring you have for your original thermostat would work for the new stat except that the blue wire going to X2 on old stat would go to W2/Aux-E on the new stat.

As stated before, you will need to run a new wire to the stat to connect a C wire or use the G wire as a C wire. To do that, at the stat you move the G wire to the C terminal. At the air handler you move the G wire to the B terminal and install a jumper wire between Y and G terminals at the thermostat. Using the second option. you lose manual control of the blower.

It will take some time to figure out, but there are plenty of people on the forum who are more than capable to help sort it out.
 

Last edited by firedawgsatx; 01-06-15 at 10:14 PM.
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Old 01-07-15, 08:59 AM
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Very much appreciate the responses. I will see if I can get some more pics up of the terminal at the air handler. There are certainly plenty of wiring bundles!

I plan on moving forward with the G wire option as I don't mind giving up manual control of the blower. Here's what I don't quite understand: does the Trane not use a common wire at the tstat, hence all of these problems? It feels like I'm having to convert from an ancient system to a new one, but the "old" unit isn't very old. So much for the easy conversion. Again, thank you for the speedy replies!
 
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Old 01-07-15, 09:33 AM
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To prevent the comfort control and heating/cooling system from shutting down due to lack of battery power, it is not recommended that the comfort control be solely powered with the three AAA batteries during normal system operation
When the system was installed.... a new thermostat cable should have been pulled. Apparently it wasn't in the budget.
 
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Old 01-07-15, 09:33 AM
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Yes, Trane definitely uses a common wire at the thermostat. On a Trane thermostat it designates the common terminal as B. That translate to a C terminal on most other thermostats. The problem you are having is that the installer did not run a thermostat cable with the proper number of conductors for a 3H/2C system.

Did all system functions work properly as it is wired at the air handler?
 
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Old 01-07-15, 10:11 AM
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On the old stat w1 =Aux, and X2 = E.
If the new stat only has a single Aux/E terminal for both of these wires you can connect blue to B at the air handler and connect blue to C at the new stat.
 
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Old 01-07-15, 05:41 PM
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That would explain a lot. I pulled the comfort control and the system won't run.

Also,

On the old stat w1 =Aux, and X2 = E.
If the new stat only has a single Aux/E terminal for both of these wires you can connect blue to B at the air handler and connect blue to C at the new stat.
yes, this is indeed the case. But when I connected blue to C at the new stat (blue already connected to B at the handler), the stat would not power up.

As was previously mentioned, I need to investigate using the green wire option or pull another cable (unlikely). Stay tuned...
 

Last edited by phatkrome; 01-07-15 at 06:16 PM.
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Old 01-07-15, 05:49 PM
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Did you turn off power to the air handler before removing the thermostat wires? If not, you may have blown the low voltage fuse. Trane usually uses a 5 amp automotive blade style fuse. If a control board is not installed many times the fuse will be wired in as shown in the second attached photo.
 
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Old 01-07-15, 07:24 PM
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Did you turn off power to the air handler before removing the thermostat wires? If not, you may have blown the low voltage fuse. Trane usually uses a 5 amp automotive blade style fuse. If a control board is not installed many times the fuse will be wired in as shown in the second attached photo.
I tried to be consistent about shutting off the power but can't say that was true 100% of the time. Having said that, I went to the air handler but I could not locate this fuse anywhere. I did not start removing parts so if it was behind something, I missed it. If it is blown, what would not work?
 
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Old 01-07-15, 07:37 PM
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If you find the transformer in the air handler follow the red wire coming from the low voltage side and going to the R terminal on the terminal board. If there is no fuse, the transformer could have been fried. If you don't see a fuse as shown in my last post, look for an in-line fuse holder as shown in the attached photo. I will check my files to see if I can find a schematic for your air handler.
 
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Old 01-07-15, 07:59 PM
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I was able to find a wiring schematic for your air handler. The schematic shows there is a fuse spliced into the red wire between the transformer and R terminal as shown in the attached diagram.
I outlined the wire in red and show the fuse outlined in orange.
 
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Old 01-08-15, 07:40 AM
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There should be 2 wires on air handler B. This indicates that you have some wire nuts between the 2 points.

Verify that the bundle of wires that includes your green fan wire on G also contains the blue wire that we will now use for 24 volt common (B). (And replace that fuse)
 
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Old 01-09-15, 01:18 PM
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I'm going to try and tackle the fuse situation this weekend, so that should be interesting. In the mean time, a quick follow up on this:

As stated before, you will need to run a new wire to the stat to connect a C wire or use the G wire as a C wire. To do that, at the stat you move the G wire to the C terminal. At the air handler you move the G wire to the B terminal and install a jumper wire between Y and G terminals at the thermostat. Using the second option. you lose manual control of the blower.
If I use the G wire, I'm left with the following at the stat:
C - green
W-O/B - orange
R/RC - red
??? - white
Y - y
G - ???
W2-Aux/E - blue
Y2 - brown

Do I now have an extra wire at the stat, and don't use the G terminal?

Also, based on the following (which you thankfully provided!!) the wiring should be as follows:

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So, at the stat, all 7 wires are there, but the blue wire is connected to X2, rather than the B terminal. This is the only difference I can see between the diagram and actual. Did the installer do something incorrectly? Earlier comments indicate a new cable should've been pulled but it looks like all wiring is accounted for. Also, all wires are also installed correctly at the air handler as seen in my earlier pic. Thanks!!
 
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Old 01-09-15, 01:49 PM
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You needed 8 wires at the thermostat to properly operate your 3H/2C system. You have only 7.
You do not have a wire to connect to the C terminal. That is why you must take the wire normally used for G and re-purpose it for the C wire for your new thermostat.

Since you will be using the G wire for the C wire you will not have a wire on the G terminal when done.
The white wire and the X2 (blue) wire will both go to the W2-Aux/E terminal.

When complete, the wires should land:

C - green
W-O/B - orange
R/RC - red
W2-Aux/E - white
Y - yellow
G - nothing
W2-Aux/E - blue
Y2 - brown

Here is a link to the installation manual for your air handler:

http://www.dortonairconcepts.com/pdfdatabase/ptee.pdf

There is a wiring diagram on page 21 that shows wiring for a single speed heat pump. Of course, yours is a two-stage so the wiring will be modified as shown in the heat pump manual.

The white wire on the W2-Aux/E goes from the thermostat to the air handler to activate the auxiliary heat strip(s) when the heat pump can't keep up with maintaining set temperature.

The X2 wire is to energize emergency heat when the heat pump outside breaks down, In emergency heat mode the heat pump is locked out and only the electric heat strips are energized to provide heat until the heat pump is repaired. The X2 wire from the heat pump to the air handler energizes the heat strip(s) to temper the air when the heat pump is in defrost mode.
 

Last edited by firedawgsatx; 01-09-15 at 03:00 PM. Reason: Added link
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Old 01-09-15, 09:47 PM
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Why land white and blue on Aux/E?
I would connect white to Aux/E and connect blue to C at the stat.
The blue that is not currently connected to B at the air handler must be moved to B from the wire nut connecting it to the white wire at the air handler.
 
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Old 01-16-15, 12:33 PM
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Hey all,

I just wanted to follow up with a final outcome to this situation. Over the weekend, I ended up going through the rat's nest of wires at the air handler to see what was going on. It turns out that I had one blue wire tied up into the the white which I suspected may be the case after this comment got me wondering what exactly was going on with blue/white schematics:
Why land white and blue on Aux/E?
I would connect white to Aux/E and connect blue to C at the stat.
The blue that is not currently connected to B at the air handler must be moved to B from the wire nut connecting it to the white wire at the air handler.
So, once disconnected, the blue now acted properly as the the common. It never made sense why the stat was wired in a way that didn't follow the Trane diagram. Everything seems to be running well (might I even say better?). All functionality is present including manual control of the blower.

Also, I finally tracked down the fuse - it was ceramic which is why I missed it earlier (and not blown).

Again, thanks for everyone's help on the forum!!
 
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Old 01-16-15, 08:08 PM
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This is great news

You have a fantastic weekend
 
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