Question about Aprilaire 700 Humidifier

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Aprilaire 500A Do I need 24v transformer

If furnace has the 24v terminals, do I still need the transformer. Also which is better to mount on cold air side or supply?

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If the funace has the 24 V you should use that but test it first with a call for heat to make sure it is 24 and not 120 coming out of that terminal!!!!!
Mount on cold air side with the bipass going to the supply.

Posted on Jan 19, 2009

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If i hook my Aprilaire 400 Manual (not auto/digital) humidifier up straight to a 24v wall outlet instead of to the furnace, will it still work correctly? Or does it need to be powered by the furnace to...


Your humidifier is a bypass type. The only voltage needed is 24vac to open the water valve. Air only flows through the humidifier when the furnace blower is running, and the wet pad will add very little humidity if the furnace is not running and heating the air before flowing through the wet pad in the humidifier.
It is best the water valve is only energized when the furnace is running. Some furnaces have a connector on their control boards labeled HUM for this purpose. Test it's voltage when the furnace is running because some will output 110vac instead of 24vac you need.

Jan 31, 2013 | Aprilaire 400 Humidifier

1 Answer

Is Aprilaire 500M suppose to turn on when furnace motor turns on?


The humidifier should turn on and off with the blower motor of the Furnace. This can be done by wiring the the humidifier to the HUM terminal on the furnace control board and then stepping down the power with a transformer. If the humidifier has it's own tarnsformer then a current sensing relay can be used by attaching it to the blower motors common wire.

Jan 13, 2013 | Aprilaire Humidifiers

1 Answer

Have a aprilair 550 for some time. Installed a new Lennox G61MP furnace and the technitions failed to reconnect the wiring that powers the humidifier. Need wiring schematic. Does humidifier transformer get...


Hello, yes the transformer will get a 120 volts from the Furnaces control board, there should be a terminal labeled HUM on the control board. You need to bring 2 wires one from HUM and one from a nuetral tap on the board to the line side of the transformer, this way every time the blower motor on the Furnace turns on the humidifier will aswell.

Aug 23, 2011 | Aprilaire 550 Humidifier

1 Answer

I have no idea how to wire my Humidifier to the furnace! I am attempting to wire an Aprilaire Humidifier to an older furnace. The supplied wiring instructions are of no use to me because I have no terminal...


Hello, if the transformer you got with the humidifier is one that plugs into a receptacle than all you need is either a current sensing relay or sail switch. First connect one wire to transformer then connect to humidiistat then to either sail switch or current sensing relay and back to other terminal on transformer. if you use a sail switch then it will mount in the return air duct if you use a current sensing relay it will cradle the blower motors common wire. I will post a pic of both robhvac47_19.jpg current sensing relay

robhvac47_20.jpgSail switch

Feb 20, 2011 | Aprilaire 550 Humidifier

1 Answer

Connecting an Aprilaire 700M to my HVAC system. I do not have the wiring diagram for the fan control board for the HVAC system. Aprilaire diagram says to wire the 120VAC to 24 VDC transformer to the HVAC...


If you don't have a volt meter, purchase one. I've seen them as low as $20.00 at Sears and even lower at Home Depot and other discount stores. The HUM terminals are most likely low voltage (24v). The "N" is the neutral. Assuming you have confirmed this is low voltage (24v, you will use HUM and "N" terminals. This control sequence is typically to allow for operation of your humidifier only when there is a call for your fan to run. The brown wires coming from your Humidifier are your low voltage circuit. One should be directly wired to "N". The other should be ran to your humidistat. The other side of the switch of your humidistat should be wired to the HUM terminal.
I hope you will find this helpful. Good Luck!!!!

Feb 06, 2010 | Aprilaire 700 Humidifier

1 Answer

Why two 24 Vac on aprilaire 700's control unit?


Okay, I looked up the installation manual online to see exactly what you are working with.
Yes the R anc C need to be hooked to the transformer supplied with the unit. The primary 120v side needs to be hooked into the power coming into the furnace. this can easily be done were the L and N get hooked into your furnace or circuit board on the furnace. This will provide the contiuous power to the unit. Preferably you will hook this after the door switch of the furnace so that you will kill the power toit if you take the blower door off.
The ODT terminals are for the outdoor sensor if you want to hook that up it will vary the humidiy in your home according to the outdoor temperature then.
Now the W/G and Cf terminals. If you have 24v coming from the HUM terminals of your furnace you DO NOT need a second transformer. You must check your furnace manual or check the voltage to them with the furnace blower energized. The HUM terminals will only have power to them when the blower should be running.
If the HUM terminals are 120v then you need to get another transformer and hook up the primary side to the HUM terminals so it is powered only when the the blower is running. Hook the secondary side to the W/G and Cf terminals.
So bottom line is that you need to figure out what voltage your furnace is giving to the HUM terminals and then go from there. Some times the EAC terminals or the ACC terminals will be 24v on the furnace board. Either of them could be used also, as they are only energized when the blower is running also.

Heatman101

Jan 25, 2010 | Aprilaire 700 Humidifier

1 Answer

No water flowing to water panel but have water to the solenoid. I have a Aprilaire model 550. wondering if the solenoid is bad and how do I check it.


To test solenoid, apply 24V directly to the terminals as see if water flows through it. Alternativly, turn everything on, ensure that there is 24 volts accross the solenoid wires, if you show 24Volts and no water, solenoid is bad. To test you will need to set your meter to AC Volts.
If you have a separate black transformer supplying the 24 volts, hook that directly to the solenoid. You may also be getting the 24Volts from your furnace circuit board, if that is the case you will see two terminals usually marked HUMIDIFIER on the furnace circuit board (you will need to open your furnace usually 4 screws or so.) There is 24 volts there WHEN THE HEAT IS ON , run two new wires from those terminals to the solinoid and see if it passes water cuz that is when those terminals have voltage. Best way is with a meter though and if you have 24 volts at the solenoid AND no water, it is bad. If NO VOLTS, then could be the the humidistat or a disconnected wire somewhere in the path.

Dec 26, 2009 | Aprilaire Humidifiers

1 Answer

Water runs when furnace is off, but stops when furnace is on.


the 760 humidifier does not need a transformer wired externally. the 760 has its' own 24v transformer inside the fan compartment. this transformer will provide the power to enrgize the water solenoid as needed. it sounds like to me the additional trasnformer is hot all the time. when the furnace comes on, the unit gets power and the internal transformer is cancelling the power from the external transformer. this would explain why it quits running when the heat is on. since the external transformer is hot all time, when the heat shuts off, the solenoid is getting energized by the external transformer. to make this run correctly, you need to get rid of the external transformer. leave the humidifier high voltage wires hooked up so they are only hot when the furnace runs. if you have a humidistat that has a r and c terminal, you will need to wire these directly to the r and c on the furnace control board and move the switch inside the humidistat to "power". make sure it is not on "bypass". then wire your 2 brown wires from the humidifier to each of the "h" terminals on the humidistat. if you have a humidistat that only has 2 terminals, wire one brown wire to each of the terminals. this should allow it to run properly.

Jan 28, 2009 | Aprilaire 700 Humidifier

1 Answer

Wiring problem


Sounds like you may have put 120v through a 24v solenoid and humidistat.
Is the HUM terminal on the furnace 120v or 24v?
If it is a 120v terminal you will need a 120x24v transformer and a new solenoid and maybe a new humidistat.

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3 Answers

Aprilaire 600 only operates in test mode...


Call Aprilaire and tell them, this is happining everywhere

Dec 05, 2007 | Aprilaire 600 Humidifier

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