Author Topic: Help GeneralAir Humidifier 900CSW Wiring  (Read 336 times)

Offline tdibratt

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Help GeneralAir Humidifier 900CSW Wiring
« on: February 23, 2017, 10:29:44 AM »
HI there I purchased the Generalaire 900CSW with the General Aire MHX3 Humidistat.

Seller indicated to connect to W and C on Furnance control board so when a call for heat the selenoid would be energized with 24V AC

I have a Keeprite G9MVE0801716 dual stage furnace

Recently upgraded the thermostat to Nest and Nest can control humidifier

The question is, there is a HUM terminal on furnace but I believe it's 110V and comes on when a call for Heat.  That would require a step down transformer to 24AC which did not come with the humidifer.  Hence it is wired using the W and C on the control board using the 24VAC switch via the thermostat and using the onboard furnance voltage

If I connect up the "*" on Nest for Humidifier control, would I just wire it up with a wire connector in the furnace to the wire that goes from Humidifier to the W terminal (remove it from W) which goes to the Humidistat?  And turn up the Humidistat to top reading?

There is a DHUM terminal on the furnance control block but not sure it makes sense to connect the wire from the Nest "*" to DHUM and then the wire from Humidistate to DHUM vs just wiring them up directly off the control board.

Thx

Offline Porcupinepuffer

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Re: Help GeneralAir Humidifier 900CSW Wiring
« Reply #1 on: February 23, 2017, 12:16:39 PM »
The hum terminal should be 24vac. No need for a step down transformer on this furnace.

Offline tdibratt

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Re: Help GeneralAir Humidifier 900CSW Wiring
« Reply #2 on: February 23, 2017, 12:36:40 PM »
If it's live when call for Heat at 24VAC then I presume it would be a wire from HUM and COMMON out to the manual humistat.  But I want to control with my NEST so not sure I can use that, can I?  How would I wire it in with NEST?

Thx

Offline Admin

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Re: Help GeneralAir Humidifier 900CSW Wiring
« Reply #3 on: February 23, 2017, 02:19:53 PM »
The NEST supplies 24V on the * terminal.  Connect wires to the humidifier solenoid and bring those wires into the furnace blower cabinet.  Connect 1 wire to the * wire coming from the thermostat and connect the other wire to the C terminal on the furnace control board.  Then enter the NEST pro menu and setup the humidifier to run with heat.

Also if the furnace is set for a 2 stage thermostat and you wired W and W2 between the NEST and furnace, wiring to W will only give you low stage humidity.  Using the HUM terminal would work for both low and high stage.

You're best to eliminate the humidistat and use the NEST.

Offline tdibratt

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Re: Help GeneralAir Humidifier 900CSW Wiring
« Reply #4 on: February 23, 2017, 02:32:23 PM »
thx

Offline Sergroum

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Re: Help GeneralAir Humidifier 900CSW Wiring
« Reply #5 on: February 24, 2017, 12:00:05 AM »
Here's a question. Is NEST really that much better then a humidistat? Humidistat if placed on a return, senses the humidity of the averaged out air of the entire house. The nest only senses in the nearby vicinity.

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Re: Help GeneralAir Humidifier 900CSW Wiring
« Reply #6 on: February 24, 2017, 09:11:45 AM »
Well you're right a humidistat mounted on the return will probably give you more accurate readings.  I'm not 100% if the NEST has window frost control, but it knows the outdoor temperature and humidity and may adjust the indoor humidity to prevent moisture and ice forming on the windows.  I know the Ecobee3 has this feature.  It's similar to what you would get with any automatic humidistat with outdoor sensor.