Thermostat has no C terminal


  #1  
Old 07-12-22, 10:02 AM
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Thermostat has no C terminal

My daughters house is a gas heat with electric A/C.
I want to upgrade my daughters thermostat to a wifi programmable one.
The old thermostat does not have a C terminal and only uses the following:
Blue wire to B term
Green wire to G term
Yellow wire to Y term
White wire to W term
Red wire to R term and jumper to RC term.

I went to honeywell's site and used some app on there to help pick a new thermostat. After telling it which wires I had and what terminals were in use, it said it couldn't help me and to contact a professional.

Any ideas on a programmable thermostat that would work? Wifi is a preferred option, but not a requirement.


 
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Old 07-12-22, 10:24 AM
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Welcome to the forums.

Assuming you have a Trane or Trane branded furnace.....

R --------> red -----------> R
W -------> white --------> W
Y --------> yellow -------> Y
G -------> green --------> G
B -------> blue ----------> B

Any thermostat in the Honeywell line will work for you.

Correction; B is not a C. Terminal. B is stating that this is a heatpump system.
 

Last edited by PJmax; 07-20-22 at 04:19 PM.
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Old 07-18-22, 08:47 AM
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Thanks

Thanks PJmax,

I don't know the brand of the furnace as all the labels are unreadable.

What about the jumper between R and RC?

Thanks
 
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Old 07-18-22, 08:51 AM
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Most thermostats come with a jumper..... just leave it.
 
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Old 07-19-22, 04:20 PM
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Hi, to be sure that you have a Common, test between R &C with a multimeter, you should get 24VAC
Geo🇺🇸
 
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Old 07-20-22, 02:35 PM
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On that thermostat B is a B. You can see on the backplate that the "not used" pin is C.

Best to get a picture of the wiring at the furnace end. The blue wire might not even be hooked up to anything.
 
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Old 07-20-22, 04:22 PM
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Good catch Astuff.

There is no C wire present there.
B suggests you have a Rheem or Ruud heat pump.

You MUST confirm exactly what equipment you have.
 
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Old 08-04-22, 11:30 AM
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I want to thank everyone for their input. So I was finally able to get back over to her house and look at the furnace.

Looking at the terminal block in the furnace, the wires are as follows:
R - R
Y - Y
G - G
W - W

B is not connected to any terminal in the furnace.

Can I connect the blue wire to the C terminal in the furnace and to a C terminal in a new thermostat?
 
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Old 08-04-22, 12:37 PM
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Yes... you can connect the blue wire like that.
 
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Old 08-05-22, 07:57 AM
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Thanks for all the assistance.
 
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Old 08-23-22, 12:49 PM
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Thanks to everyone. Finally got back over to her house. Got the new thermostat wired in and working great.
 
  #12  
Old 08-23-22, 04:12 PM
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Good job. .. . Thanks for letting us know all went well.
 
 

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