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Old 04-17-2012, 02:50 PM   #1
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control furnace fan


Old Gas Furnace (Anthes LCB120)
Original 2-wire

I'd really like to control the fan upstairs with my new thermostat (2,3, 4+ wire capable); so I'd like to set it up as 3 wire (adding a 3rd "G" wire).

These furnace photos should be enough to explain what I have; photo 7 is the Fan Control. Right now there are 2 wires running from the thermostat (hooked up as 2 wire) to the blower (smaller white wires in photo 5). NOTE: the photos look broken with red X's on them but I clicked them and they show up???

The answer might be a FAN relay something or other but what should I ask for/buy and how would I hook it up with my current setup?

Could someone please help me out?
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Last edited by ssstan69; 04-17-2012 at 02:53 PM. Reason: the photos look broken with red X's on them but I clicked them and they show up???
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Old 04-17-2012, 04:07 PM   #2
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control furnace fan




Low voltage on bottom, r and c which is most likely what you have, and high voltage that is going through your fan limit to the blower across the top.

What the fan limit is doing is bringing on the flames and at a certain temperature allows the fan to come on. What you're going to need to do is take the fan limit off circuit and bring the wires through this new fan relay.

I'm not exacly certain how to go about keeping both, heat and just fan on on your configuration, as currently on call for heat the low voltage needs to go through the gas valve (as pictured in your pics) and then on call for fan it needs to go only through the fan relay.

Maybe someone with more experience with controls will chime in.

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Old 04-17-2012, 07:31 PM   #3
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control furnace fan


I am not seeing your photos????

My memory of an anthes makes it pretty straightforward though. Single speed blower with a 3 wire all 120V fan/limit control

A 24V/120V isolation relay will work fine.
"G" line from stat goes to one side of the 24V coil with the coil's other 24v connection going to neutral.
You can take 120 Volts from the junction box or "T" into the 120 supply for the fan/limit control to power the 120V side of the relay. The other side of the 120V relay connects to anywhere along blower supply line after it leaves the fan/limit control. What you need to be sure of is which line on the top of your fan/limit control is the blower line and which is the limit heading down to power the transformer.

Your G line pulls in the coil and connects the blower to 120V.

Now I see your photos, That's a 40YR+ furnace.

Last edited by how; 04-17-2012 at 08:00 PM.
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Old 04-19-2012, 10:16 AM   #4
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control furnace fan


thank you for your replies...
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