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Old 07-31-2020, 07:40 AM   #1
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A/C Thermostat Wiring


Hey! Trying to indentify the "C" commom wire for a new smart thermostat. My am currently using a Honeywell thermostat that only requires 3 wires (Red, Yellow & Green). The Blue and White are wrapped around the bundle since I only use this thermostat for my AC. Would the other end of the "C" wire be only my outside unit, or up in the attic where the AirHandler is? Or??? Would really hate to spend the $$$$ for a simple wire hook up! Thanks in advance.
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Old 07-31-2020, 08:04 AM   #2
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A/C Thermostat Wiring


Hey! Trying to identify the "C" common wire for a new smart thermostat. I am currently using a Honeywell thermostat that only requires 3 wires (Red, Yellow & Green). The Blue and White are wrapped around the bundle since I only use this thermostat for my AC. Would the other end of the "C" wire be only my outside unit, or up in the attic where the air handler is? Or??? Would really hate to spend the $$$$ for a simple wire hook up! Thanks in advance.
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Old 07-31-2020, 08:05 AM   #3
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A/C Thermostat Wiring


Up in the attic air handler you should have a board where the thermostat wire connects. You could possibly have a c terminal to hook up to there, just by attaching one of the unused wires to c on the board and then the same color wire to c on the thermostat
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Old 07-31-2020, 08:20 AM   #4
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Re: A/C Thermostat Wiring


The other end, as said, will be in the air handler.
Hopefully your not planning on a nest thermostat.
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Old 07-31-2020, 08:32 AM   #5
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Re: A/C Thermostat Wiring


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Originally Posted by roughneck View Post
The other end, as said, will be in the air handler.
Hopefully your not planning on a nest thermostat.

Youíve been in the trade a while? Usually all the older hvac guys hate nests for some reason lol but as long as you have a c wire itíll be fine. The only issues Iíve seen with nest is when thereís no c wire and it tries to ďsteal powerĒ from R, and it makes aquastat relays chatter.
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Old 07-31-2020, 08:40 AM   #6
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Re: A/C Thermostat Wiring


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Youíve been in the trade a while? Usually all the older hvac guys hate nests for some reason lol but as long as you have a c wire itíll be fine. The only issues Iíve seen with nest is when thereís no c wire and it tries to ďsteal powerĒ from R, and it makes aquastat relays chatter.
The nest has issues beyond the C wire problems.
Iím 36 years old and embrace technology within the trade, but I wouldnít have a nest if you paid me to use it. My customers have paid me a lot of money in service calls because of those things.
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Old 07-31-2020, 08:56 AM   #7
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Re: A/C Thermostat Wiring


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The nest has issues beyond the C wire problems.
Iím 36 years old and embrace technology within the trade, but I wouldnít have a nest if you paid me to use it. My customers have paid me a lot of money in service calls because of those things.

Thatís why I ask, all the old guys at the shop hate it because they donít understand it or just hate tech lol. Nest offers a bunch of training for contractors through their site. I personally love nest, I only have seen issues where customer donít have a c wire. What other issues have u come across?
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Old 07-31-2020, 09:08 AM   #8
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Re: A/C Thermostat Wiring


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Thatís why I ask, all the old guys at the shop hate it because they donít understand it or just hate tech lol. Nest offers a bunch of training for contractors through their site. I personally love nest, I only have seen issues where customer donít have a c wire. What other issues have u come across?
Subbase problems.
Horrible product support.
Electrical short issues that has taken out boards and other electronics in the HVAC equipment.
Extremely high price for a subpar product compared to Honeywell and Ecobee.
Poor comparability with zoning systems.
Runaway situations where the customers equipment gets stuck running constantly in heating or cooling.
Linking problems with the customers WiFi.
Poor firmware resulting in elevated energy bills for the customer.
One actually caught fire on the wall.
And so on......
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Old 07-31-2020, 09:14 AM   #9
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Re: A/C Thermostat Wiring


One caught on fire!? Jesus! Lol Actually i have heard of sub base issues too. I think ecobee makes a geo fence model thatís battery operated. That could be a good alternative for this guy if he has no C wire.
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Old 07-31-2020, 10:28 AM   #10
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Re: A/C Thermostat Wiring


I really appreciate all the helpful responses. Indeed it was disconnected at the Air Handler Unit. All is good now. Truly appreciate the help and the savings! No it is not a nest. Is a Honeywell Smat Color Thermostat RTH9585WF.
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Old 07-31-2020, 02:39 PM   #11
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Re: A/C Thermostat Wiring


Welcome to the forums. Hopefully you got this in the AC section as well.
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Old 07-31-2020, 06:43 PM   #12
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Re: A/C Thermostat Wiring


In the attic at the air handler
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