Replacing Humidistat


Old 11-20-04, 03:46 PM
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Replacing Humidistat

I'm somewhat new to this so don't assume I know anything!

My cold side duct mounted Aprilaire 560 will not turn on. Checking circuits I believe I have traced the problem to the Humidistat. It is a Honeywell sail type model H49B. I removed it from the duct and gently cleaned it - still no luck. Looking at this thing I'm guessing it has been replaced by something much less mechanical, probably electronic.

Is there a humidistat available that would be a direct retrofit replacement?

Any suggestions?

Old 11-20-04, 04:00 PM
Ed Imeduc's Avatar
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Location: Mountain Williams Missouri
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If I have this right here .That sail switch is what would let it turn on when the blowe came on. Now to replace that you want a A50 current sensing relay. This will just go down over the blower wires. So when the blower turns on the humidifier will come on. This is not a humidity control you should have one on the duct there also. It works like this . The blower comes on the A50 tells the humidifier to turn on but it has to see if the humidity control said to turn or not.

Old 11-21-04, 11:17 AM
hvac4u's Avatar
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i am with ed

a model 50 relay will be installed in the blower compartment, with the heat speed wire running through the loop in the relay

when the motor is running in that speed, it will close a switch between the 2 wires coming out of the relay, letting the humidifier know the fan is on

you will still need a humidistat or the humidifier will run whenever the heat is on

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