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Re: furnace blower wiring

From: info@builderswebsource.com
Category: HVAC
Remote Name: 63.198.181.43
Date: 12 Nov 2001
Time: 11:26 PM

Comments

It sounds like you may have an older "millivolt" type furnace system, which uses only two wires (Red and White). More modern furnaces and thermostats use a 24-VAC system with 5- or 7- conductor 18-gauge thermostat wire that follows this color code:

(5-wire) White, Red, Green, Blue, Yellow

(7-wire) White, Red, Green, Blue, Yellow, Brown, Orange

White (W marking) is the primary heat call relay.

Red (Rh marking) is the power from the heat system (24V)

Green (G marking) is the Fan relay (blower)

Black or Blue (C marking) is the common of the 24VAC transformer

Yellow (Y marking) is the primary cooling call relay (if you have an air conditioning system)

Brown (E marking) is the emergency heat relay

Orange (O marking) is the change-over relay to cool relay.

So, for a heater only system, you'll need at least the first 4 wires, which include W,R,G,C

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