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I'm trying to install a thermostat that uses a common wire.

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However, I am using an...
I'm trying to install a thermostat that uses a common wire. However, I am using an unused wire which is blue as the common. I connected the blue wire at the furnace, but nothing happened. So, I took my tester and there seems to be no voltage coming from the common at the change board. Any thoughts?
Submitted: 1 year ago.Category: HVAC
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Answered in 5 minutes by:
12/20/2015
HVAC Technician: Phil, Mechanical Engineer replied 1 year ago
Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6,022
Experience: Retired HVAC/ Electrical & Boiler contractor. Industrial
Verified

Hello,

Check for 24 volts *between* R and C....tell me what you get.

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HVAC Technician: Phil, Mechanical Engineer replied 1 year ago

You should get 19 to 24 volts from R on the thermostat terminal strips either in the furnace or at the thermostat to *ground.

Sometimes C wire will not give a voltage read to ground, in that case the system was designed to have a grounded common (C) wire. So that you need to measure voltage

**between** R and C.

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Customer reply replied 1 year ago
Okay, I don't have a meter handy. I will return.
HVAC Technician: Phil, Mechanical Engineer replied 1 year ago

.

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