# Caddy Add-On Wood Furnace Install....wiring burner relay



## WildwoodHill (Nov 14, 2009)

I recently installed a Caddy Wood Burning Add-on furnace connected up with my Lennox LP gas furnace. I'm hoping someone on the forum that has installed such a setup can help. I have everything working except I am having trouble getting the burner relay/gas valve to operate properly on my gas furnace. The wiring diagram and the folks at SGI in Quebec that manufactured the furnace say to wire from the wood burning Caddy transformer (red and black wires) to the connections on the gas valve/burner relay of my gas furnace. This has not worked. It will not cause the furnace gas valve to release and ignite. Do I need to tie in the wires from the Caddy into the existing gas valve/burner relay wires on the gas furnace. These wiring directions are not very clear in the manual and leave out the details. If anyone has experience with this aspect and can provide advice I much appreciate it!

So far the caddy add-on has used very little wood and heats our house just fine...will have to see how it goes come January. It feels great to be able to provide my own wood to heat our home without much need for gas.

Thanks!


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## laynes69 (Nov 14, 2009)

I have a 1950 (Caddy) but mine is a parallel installation due to the unit having a blower with it. According to the directions, the Add-on should have both the thermostats wired together with the Interlock relay. The purpose of the relay is if the plenum temperature exceeds 150 degrees, the gas furnace won't fire. Have you tried to fire the gas furnace when the woodfurnace was cooled? Our old woodfurnace was installed in series, and I ran 2 wires from the limit/control to the r and g on the board of the gas furnace. No interlock needed, and it worked fine. But that interlock is used as a safety device on the furnace. So the 2 wires from the interlock should go on whatever energizes the burner relay which in return will fire the central furnace when the plenum of the woodfurnace drops below a set temp and heat is required. I know caddyuser on here has his in series like you do. I'm sure he will chime in and put you in the right direction.


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## WildwoodHill (Nov 15, 2009)

Thanks very much Laynes69 for those tips. I had earlier tried going to r and g thinking that was the logical connection, but that did not work either. I've included a photo of the gas valve on my lennox lp gas burning furnace that is connecting in series with the Caddy Add-on. You can see the taped orange and yellow wire that were the original connections on the gas valve and I've connected the red and black wires from the Caddy interlock relay (2nd photo) to the gas valve T connections. However, this new connection acts like the gas furnace will fire, but it never does. On the other hand with only the original orange and yellow connections back on, the gas furnace will fire once the room temperature drops below both wood and gas thermostats....but it then won't shut off...it continuously burns and heats until I shut off the power. somehow the interlock relay must connect with whatever signals the gas valve to release.

My only other thought is that the red and black wires from the Caddy interlock relay should be connected together with the orange and yellow gas valve wires that were connected in the first place. I just don't want to fry the control board in my lennox furnace, if there is any danger in that. Everything else is working great, except for relay to the gas furnace to kick on and shut off when thermostat temp drops and calls for heat.

If you, CaddyUser, or others that have faced such a connection can offer further insights it is greatly appreciated!


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## Gooserider (Nov 15, 2009)

I am just guessing here, but what I'm wondering is if you are tyeing into the gas furnace in the right place?  If you were just running the gas furnace w/o the Caddy, where would the thermostat connect?  I would expect that the Caddy control would connect in the same place...  Presumably one should let the furnace itself control the gas valve, and just worry about sending a control signal to the furnace...

From what  laynes69 is saying about his setup and the interlock relay, it would sound to me like your gas thermostat should go to the interlock relay, and then the wires from the interlock relay connect to where the thermostat wires would on the gas furnace...  That way if the gas thermostat calls for heat, it will signal to the interlock relay, which might or might not pass the signal on to the gas furnace depending on the plenum temperature...

I'm not an expert on how the furnace should be connected, so I might be way off base...  The other thing to look at is to make sure that all the voltages are correct, and that you have hots going to hot, and so on...

Gooserider


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## laynes69 (Nov 15, 2009)

Thats right. The part that is in the left picture is a Fan center control. I'm not sure that part will work because the manual calls for an interlock relay. The part # is 8a05a-4 and is the part used in the manual.


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## WildwoodHill (Nov 15, 2009)

What you guys are saying makes complete sense. I'm going to see about rethinking this and connecting to thermostat controls on the furnace and let the furnace control the gas. Whatever energizes the gas release and controls that is where I need to hook into. I'll post back and let you know how this turns out. Thanks again for your thoughts on this!


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## laynes69 (Nov 15, 2009)

When you connect to the board you must make sure its low voltage. A quick way to fry the board. My old setup used r and g for fan only on the central furnaces board. If the gas needed to run, then a relay in the board would shut off the blower, energize the board and the heat would cycle until met then as long as the woodfurnace was calling for heat it would continue to run. The only problem I seen was if the central furnace didn't fire correctly, then it could potentially shut down and at that point, you loose the blower for the woodfurnace. If I had an add-on that whats I would do. The important part of that would be that the thermostat controls the damper on the caddy, and the limit is controlling the damper in case it get too hot so it can close. How did you tie into the blower on the gas furnace from the caddy?


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