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I am attempting to change my thermostats and ran into some…

Customer Question
Hello, I am attempting to...
Hello, I am attempting to change my thermostats and ran into some puzzling items I’m not sure about. Gas furnace electric AC
There are two sets of wires running to thermostats 2 strand and a 5 strand
First There are two wires connect to W one goes to W on furnace and other to C on furnace. What purpose does this serve?
Next there is a red wire connected to Y that runs up to thermostat, wire nutted to blue in wall then blue end in furnace wire nutted to the AC unit(seems correct just round about way) right?
From my understanding to help clean this up YCRWG all get connect to corresponding locations on thermostat and furnace then the AC wires Can get connect directly to Y and C terminals on furnace control panel?
Submitted: 4 months ago.Category: HVAC
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Answered in 15 minutes by:
11/30/2017
HVAC Technician: airheatman, HVAC Technician replied 4 months ago
airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8,977
Experience: Furnace, A/C and heat pump specialist.
Verified

I will be happy to try to help figure this out.

First of all we should not have W and C connected as that would create a dead short.

Here is what we should have:

Thermostat Furnace Outdoor

R/RC----------------R

G--------------------G

C--------------------C-----------------C

W-------------------W

Y----------------------------------------Y

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HVAC Technician: airheatman, HVAC Technician replied 4 months ago

Not sure about that but you have 2 wires from transformer.One is considered "hot" and the other is considered "Common"

Hot goes to red at thermostat. Common goes to one side of every relay in furnace that is 24v controlled as well as outdoor unit.

The thermostat is just a temp controlled light switch.

Selecting fan closes the R/G circuit sending hot back to blower relay.Selecting cool closes R/Y and sends the hot to outdoor contactor. Selecting heat closes R/W sending hot to heat circuit.

So if we connect w and C. as soon as we turn power on and call for Heat BAM direct short R to C

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Customer reply replied 4 months ago
Hmm intersting, wonder how it is still working. I’ll wire it up correctly as you indicated and clean up some of the unnecessary wires. I believe it was from when there was a humidifier control at one time. Thank you.
HVAC Technician: airheatman, HVAC Technician replied 4 months ago

May be and the white at thermostat may go somewhere else like a humidistat and the white on other end be a different white supplying common to that humidistat

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