I am scorching air with my boiler, so I guess this will fit in here. My natural gas furnace has a water to air heat exchanger in it. I will continue to use it the furnace as a backup to the boiler. I have a Hydro Air Fan control to start the pump via a relay, and I need to turn on the fan on the furnace to circulate the air heated by the boiler. The Hydro Air Han control is powered by a 24 volt transformer and sends the power to the relay for the fan.

My delima, I am not sure, but, can't I hook up the wires to the furnace common, hot (red) and blower (green) wires on the furnace, basically having a second thermostat that only turn on the blower?????? The common and hot (red) are power feeds to the thermostat from the transformer.

Am I correct on this or just asking for trouble????

Let me clearify: Since the NG furnace has the 24 volts to the thermostat, and has the wire for the blower returning, couldn't I basically hook up as a 2nd thermostat, but only to turn on the blower, no call for heat?

I am N O T your wiring and control resource - because I suck at it -- but I will key

NO

it depends

and yes - IF you interlock that call with at least a 110 degree temperature on the HX it will be blowing across. - or else your circulating a very cold draft

I have a snap disk on the exchanger that will close at 140 degrees, which will complete the ciricut that will turn on the blower. When the heat is satisified, it will turn the pump off and the blower will run till it reaches 120, which the snap disk will open and break the ciricut, then shut off the blower. Just want to be sure about running the wires to start the blower.

I hooked up to furnace, and it works. It is what the schematic shows, but the first time, I was looking for some confirmation. When the thermostat closes, it calls the secondary pump, which is on a relay, when the snap disk closes at 140 degrees, it starts the blower. Just in time for the last half of winter, hopefully.

So, everything is working, but when the fan comes on, the compressor on the a/c comes on too???? I pulled the fuse, but no idea why this comes on. The only thing I added was the C for common to transformer, R for hot from transformer and G for the fan. Any ideas? How have others that have water to air heat exchangers have their fans wired??? So far 19 degrees and NOGAS furnace, only corn running.

nogas are you sure your not touching the Y terminal on the furnace control board with that green wire?......R to Y starts the compressor.

also G and Y wires could be touching in the thermostat and you never noticed because on a call for cooling the thermostat puts 24 volts to both G and Y terminals.

not good to run that compressor in this weather.

why don't you just use the furnace transformer to start the fan?
just R to the snap disk then to G on the furnace control board.
that would start the fan

Tinman wrote:


Hi Tinman, yes very careful on hooking up. That is another option that I am now starting to understand, now that I have had some minor experience playing with the electrical side of this. I pulled the fuse on the compressor, so it wont run. The Hydro Fan controler has the common, red and green and it is attached the same to the furnace. I will pull the pannel and double check. I was wondering if somehow it is reversed on the furnace control board, though I doubt it.

I could test by putting a jumper between the red and green in the NG furnace ans see if it is trying to start the compressor too. Process of elimination. LOL

At least it is nice and warm in here this morning.

Warm is good.

Amen brother, Amen