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Old GF Humidifier water always on

1016 Views 5 Replies 3 Participants Last post by  beenthere
I have a 20 y.o. Carrier FA4ANF air handler. Somewhere along the line the previous owners installed a GF 1040 bypass humidihier with a Honeywell H49A Humidistat The supply air mounted humidistat controls a 110V solenoid, which controls the water flow.

The problem is, 110V power is constantly supplied to the humidistat, so water flows even when the air handler fan isn't running. To avoid wasting all that water, I would like the solenoid to shut off the water when the air handler is dormant. The humidifier doesn't have a float valve.

Right now, the lead to the humidistat is wired to the Carrier's fan relay, to the SPT terminal on the board. I put my meter on it and it's always 110V.

What would be the cheapest/simplest way to control the humidifier? I guess I could purchase a sail switch for $50. If I went to all that trouble, I might as well pop for $100 and get a whole new unit.

Could I install a relay somewhere?


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Sounds like its not wired to code, if its getting its 110 volts from one side of a 240 volt relay.
What would be the correct way to wire it?

Here is the service manual:

I have the furnace control board shown on page 3. The furnace wiring diagram is on page 5.

You can take 110v from somewhere else, wired through a current sensing relay rated for your VA.
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Baby steps, please. :laughing:

Should I take the 110V from the air handler itself, or run a separate outlet and plug it into the wall? Due to the location, this would be a p.i.a.

Should the current relay pick up one of the wires to the fan motor?

VA = Volts/amps?

Current sensing relay. I see lots of them for sale. What should I look for? They range in price from $15 to $50. Is this what I'm lookinf gor?
110 from another source. Yes that is the type of current sensing relay you want.
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