Hooking up Nest to Trane Heat Pump

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Old 06-14-18, 04:37 PM
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Hooking up Nest to Trane Heat Pump

Was wondering if someone can tell me how to hook up my Trane Heat Pump to the nest thermostat. Here is a picture of the wires in the current thermostat, I am just not sure where they connect to the nest. Thanks in advance.

Steve

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Last edited by PJmax; 06-14-18 at 10:45 PM. Reason: cropped/reoriented pic
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Old 06-14-18, 06:18 PM
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Use the outer labels on your old thermostat and treat the X2 as an E

I see that there is an extra wire behind the others. It would be helpful if that one could be used as a C as Nest works better with one. Trane refers to it as B. Would need to see the wiring at the air handler.

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Old 06-14-18, 06:42 PM
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Thank you. It was the x2 wire that was throwing me off. What is that wire for, aux heat? The extra wire you are referencing, is that the one in the bottom of the picture not hooked up to anything? Why would that be?
 
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Old 06-14-18, 07:45 PM
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W1 should be set up as Aux heat - runs at same time as heat pump. X2/E is emergency heat at the thermostat. When you set the thermostat to emergency it doesn't turn on the heat pump, just this wire. If you only have electric (no gas furnace) the two wires are often connected. Need to see at air handler.

Extra wire- hard to say without knowing what it is attached to on the other end. Could have been a change to your system or when thermostat was replaced they didn't know what to do with it.
 
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Old 06-14-18, 08:58 PM
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Just one correction.... W1 is not active on the nest when in heat pump mode.
You need to use the W2/AUX terminal instead.

The heat pump is stage one or W1 heat.
 
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Old 06-14-18, 10:00 PM
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Thanks guys. Just so Iím clear on this....does this look correct:

current wire Nest wire
Y2 Y2
X2 *
W1 W2/Aux
R Rh
O Ob
Y Y1
G G

and if possible, the extra wire should go to the C.

how do I know if that extra wire can go to the C? Can the next function without the C wire?

also, when hooking up the nest to a heat pump, does everything function as it should?

thanks again
 
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Old 06-14-18, 10:05 PM
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W1 is not active on the nest when in heat pump mode.
Nest changed that with a software update. Now either W1 or W2/Aux can be used for the auxiliary heat wire, just not both.
 
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Old 06-14-18, 10:11 PM
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Those connections look good. You will have to tell Nest if you have single or dual fuel. The o/b is an O, and * is emergency heat. Nest doesn't need a C most of the time but when it does strange things happen. You need to find the other end of the wire to see if it can be used.

Nest is quirky and follows unique algorithms so you will likely find something acting not as what you would expect.
 
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Old 06-19-18, 02:49 PM
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Hey guys, so I just used a multi-meter to test that un-connected wire at the thermostat and there was no reading. So I am assuming, if that is meant for a C wire, that it would also be disconnected at the handler? I am going to check the handler tonight....I think the wires will be located on the roof with the unit itself. If that is the case, Do I just connect the wire at the handler to the C (B) terminal?

Thanks
 
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Old 06-20-18, 07:57 AM
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Also, can anyone tell me where in the unit the ends of these wires will be? There are a few panels that I can unscrew, and Id rather not guess.

Thanks
 
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Old 06-24-18, 08:50 AM
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Astuff or PJMax, are you able to answer my questions above regarding the C wire? Thanks
 
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Old 06-24-18, 09:33 AM
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Should not need to go to the roof but attic/garage air handler if you have one.
As far as panels look to see where the thermostat cable comes in and remove that panel first.
 
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Old 06-24-18, 11:10 AM
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The wiring access area on an air handler will usually be very near where the electric connects to it.
 
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Old 06-27-18, 09:20 AM
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Alright Gents....so i don't have an attic, and I don't see anything in the garage, So I am assuming the wires are in the unit on the roof. Here are some pictures. The model # is Trane 4WCZ60498A1000. Any idea where the ends of the wires would be located in this unit? There is no easy access panel. Thanks again for the help.
 
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Old 06-27-18, 12:10 PM
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Ah.. Package unit so no air handler. 1st pic bottom right is where the wires are.
 
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Old 06-27-18, 01:15 PM
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Thanks Astuff. I looked in there a few days ago and saw wires, but I didn't see an end to them. I will go up there again and take some pictures and post. Appreciate the help
 
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Old 06-27-18, 02:18 PM
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Astuff, is there any other way to get continuous power to the nest (possibly using G wire??) or is the C wire the only way to do it with my set up?

Thanks
 
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Old 06-27-18, 03:38 PM
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There are several other ways but using the spare wire to connect the Nest's C to the Trane's B is best. Usually find it is a blue wire.

What is your concern?
 
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Old 06-27-18, 07:59 PM
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Astuff--Alright, found the panel. Here are a few pics. Upon closer inspection at the thermostat, the extra wire is blue. So this is what I a seeing at the unit itself (the 2 pics). Is it as easy as connecting the small blue wire to the large blue wire that has the wire nut on it? The large blue wire is connected to the B port on the panel (sorry, that picture is blurry) If it is that simple, is there a reason they didn't connect the C wire in the first place?
 
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Old 06-27-18, 08:24 PM
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PJMax, feel free to jump in on this as well. Thanks in advance
 
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Old 06-27-18, 09:37 PM
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Yes, it should be simple. Be careful putting the cover back on that you don't pinch a wire.

Hard to say what happened with not connecting that wire. Maybe they had an issue with the original thermostat? Hopefully not but maybe blue wire is bad.
 
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Old 06-28-18, 06:40 AM
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Thanks Astuff. I appreciate the help. Last question, once I connect the B wire at the unit, I can use the B wire on my old thermostat (pictured above) without an issue, correct? Right now that thermostat is battery operated. If the blue wire is good, the old thermostat should function without batteries, correct?
 
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Old 06-28-18, 10:52 AM
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It depends on model but most of the battery operated thermostats will use the B/C/common instead.
 
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Old 06-29-18, 07:39 PM
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Astuff, new dilemma, the c wire at the thermostat is too short to reach the nest. How can I extend that wire?
 
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Old 06-30-18, 11:13 AM
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Would connecting 18 gauge wire using a wire but or butt connector be acceptable?
 
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Old 06-30-18, 01:50 PM
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A short solid 18 gauge piece of wire and a wire-nut is fine.
 
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Old 07-17-18, 09:18 AM
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Ok, after 3 weeks with the nest I have noticed some weird behavior and am thinking about returning it.

I got it hooked up and it was working as it should (both stage 1 and stage 2 cooling were working as they should). Then about 1.5 weeks after getting it, the thermostat said it was cooling, but warm air was coming out of the vents ( I don't think it was the heat, i think it was just outside air). After a re-set, the issue resolved itself. We even had an HVAC guy come out and clean the coils just to be sure it wasn't the unit. Now, this morning, the same thing happened.

Astuff, have you ever heard of this happening?
 
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Old 07-17-18, 10:36 AM
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I've seen some reports of this. Some solved with maintenance which you already had done. Others had Nest replace their device but I don't recall if it solved things long term.

Returning it would be the safest thing to do.
 
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Old 07-17-18, 10:47 AM
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Thanks Astuff.

And I should be ok connecting the C wire to my previous thermostat so it can be powered now without batteries?

Would this nest issue be causing any harm to my system?
 
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Old 07-17-18, 12:19 PM
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I will miss the ability to control temp from my phone. Astuff, i was thinking about possible replacing it with a basic honey well wifi thermostat (RTH6500WF). Would my system be compatible with this, and if so, how would the wiring work?
 
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Old 07-17-18, 12:42 PM
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Sorry to blast you with responses, but the Emerson Sensi looks interesting as well....Can you tell me how I would connect the my wires to this unit as well? Thanks again
 
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