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View Full Version : Old Furnace, No G Terminal, Programmable Thermostat -> Circulate?


eightysix
Jul 3, 2016, 10:37 AM
I have successfully installed a honeywell wifi thermostat to my archaic AIRCO furnace (60's). I added the 24V 40vA transformer and c-wire. Over the winter the thermostat saved me between 2 hundred and 3 hundred dollars on the gas bill due to being off when I'm not around and off overnight because I don't forget to turn it down. It is amazing.

Now that it's summer, I sleep the furnace because if I don't, it doesn't run often enough to justify the pilot and I was wrecking a thermocouple every summer.

I'd like for the thermostat to circulate the fan, and have read as-many-as-i-can-find posts on G Terminal/Relay/Coils. Running the wire is no problem, and I've seen a couple of posts about getting a fan control center, but it seems 50% redundant considering I've already added the c-wire transformer. Had I thought about wanting to circulate the fan in the summer, I would have picked up a fan control instead of just adding the C-wire

The furnace has a honeywell L4046BXXXX fan limiter with the "push for on pull for auto" switch, the unit works flawlessly, the furnace works as well as it can, though I'm sure it isn't particularly efficient.

In labman's (awesome) posts, he recommends "digging around in the innards to find the fan motor coils/relay" and I think the fan relay is in the metal control box of the 4046B. The furnace doesn't have a G Terminal, or any terminals... or a control board, but I'd like to know where to connect a G-Wire to allow the wifi thermostat to control this very old two (now three) wire furnace.

If needed, I can get an additional relay to add to the system, but I'm assuming there must be one turning the fan limit switch on and off that I could usurp for just the fan... I just don't know to where I would connect the wire I pull from the g-terminal on the thermostat.

I can even delete this additional g-wire in the fall if needed as the only thing I need this furnace to do until October is circulate the fan... no heat, fan only, controlled by the thermostat.

Is it possible? Where do I attach a g-wire?

Thanks!