NEST wiring question


  #1  
Old 09-29-12, 05:54 PM
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NEST wiring question

Hi all, have a new Heat Pump being installed next week and already have my NEST purchased. Old Trane system has a W wire and an X2 wire (not jumpered) which I believe is just manual EM heat if the compressor fails. NEST support told me I'm compatible if I don't need the X2 wire. Can I hook the X2 to W2/AUX? I'll have Rh, W1, Y1, G, C and O/B but nothing in W2/AUX or Rc (which I know is jumpered to Rh for heat pumps). Both old and new systems are all electric with heat strip backup. NEST says they don't handle EM heat, but I'm confused by this statement on their site...

"All heat pumps need a supplemental heat source when the temperature gets cold outside (usually below 35║F). This is called second-stage or auxiliary heat and is usually controlled by the wire labeled AUX/W2 on Nest."

I don't have anything that is to be connected to W2/AUX (see bottom proposed NEST wiring)

Just W to W1.

I know I don't need T

May call them back to verify, just wanted your opinion. Thanks.

*Edit*
Since I believe W is the heat strips and does go to W1, the NEST people
said to put X2 in W2/AUX and if it didn't work, just take it out.

SORRY, did not read about pics first.

ImageShack« - Online Photo and Video Hosting

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New heat pump will be Heil ODU H4H330GKE with FXM4X3000AT fan coil

8 wires coming from my wall currently but I will not use the " T " wire so 7 to be used or 6 if I don't use the X2
 

Last edited by embryjim; 09-29-12 at 07:03 PM.
  #2  
Old 09-29-12, 07:47 PM
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YOUR wiring will be

OLD = NEW
R = RH
Y = Y1
O = OB
B = C
G = G
W AND X2 = AUX
T = NOT USED

At least that is my belief as to how it should be wired... it is very hard to say with nest. Nest actually want you to only install W to AUX and not install X2 at all. They have had a number of problems controlling heat pumps. I honestly think that NEST should have had more field testing before it was sent to market. IT IS REALLY NOT A VERY GOOD THERMOSTAT IN MY OPINION.

The problem is that you may lose a stage of heat. You are basically combining to banks of strip heaters. But it all depends on how your contractor wired your air handler.
 
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Old 09-29-12, 08:01 PM
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Well, they say you can't have two wires in one spot, and that W should go to W1 and I shouldn't need X2, or I can try X2 in W2/AUX. So I guess I'll try and if it doesn't work, return it and get a Honeywell. Thanks.
 
  #4  
Old 09-29-12, 08:23 PM
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On the nest, w1 is not used on heat pump systems. Aux is used on HP systems for your strip heaters. NEST says a lot of things, most things NEST SUPPORT is not even sure of. They dont even know what system functions a specified terminal does on old thermostats.
 
 

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