Question about Aprilaire 550 Humidifier

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Aprilaire550 water clicks on with furnance but wont click off with furnance replaced control transformer and soleniod and out door sensor

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Re: aprilaire550

Did you just install this unit, or has it been working for a while and just stopped?
1. If you just installed it, the solenoid wires (yellow) must be hooked up to switch in when you have a call for heat.
a) use a current sense relay OR
b) connect 120V & neutral to "HUM" terminal and neutral on heater control board.
2. If it has worked before, maybe the saddle valve is plugged. Turn the "T" handle all the way clockwise, then all the way out CCW. You can hear the water start flowing. Loosen compression fitting at solenoid valve to make sure water is getting there.
3) Also, you must supply 24V to the circuit to open the solenoid valve. Check your wiring. It depends on the model what way to wire it and I cannot go into that here.
4) Testing: Turn off humidistat control. Turn on heat, wait for blower to come on. Turn humidistat control to test posn. Solenoid valve should click. This will put water into top of Aprilaire tray, after few minutes it will dribble out bottom clear vynl tube to the

Posted on Jan 29, 2008

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Check to see if you are getting 24 volts from the transformer, if not, turn off power to the transformer and check the resistance of the secondary side, if no resistance the transformer is bad and need to be replaced. Also check to make sure all the wires are secure. If you are getting voltage at the transformer then bring power directly from transformer directly to solenoid valve and it should click open and let the water through, if it does then either the sailswitch/current sensing relay is bad or humidistat is bad.

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1 Answer

Water does not pass through solenoid

Thanks for your question,
first you need to determine if you have 24 volts from the transformer, if you have knowledge of electrical meters then this should be fairly easy, if not then you will need to do a little rewiring to find out if it is the solenoid, first you will need to do is shut the power off to your furnace, then get some t-stat wire, long enough to reach from the solenoid to the transformer, splice together the new wire to the wire from the solenoid, now take the other end of the wire, take the leads off the transformer (low voltage side) and hook the new leads to it, make sure the water is on, now turn the furnace back on, and if the solenoid is good the water will flow, if it doesnt, then you will need to replace the solenoid, if the solenoid does work then you know your problem lyes with the Humidistat, and you will have to replace that, but you need to determine if you have 24 volts from the transformer first, hope that helped, let us know and please rate this, thanks again ,

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1 Answer

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theholts220 - Sounds like they needed to install a bit larger transformer . You can also buy a A 50 Sensing relay that attaches to the wires for your motor and when you turn on the furnace it will allow the power to go to the humidistat. Very strange though they do not use a lot of power. Check and make sure the wires are not pinched or touching metal somewhere.

TLuzzo - The humidistat seems to be working when you turn it down. The wires for the solenoid should be hooked up to your furnace circuit board. The instruction manual will tell you where. If you dont have a spot on your circut board the A 50 sensing reley is they way to go. They are inexpensive

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That would the the 24volt soleniod valve that the water line attaches to. Steve

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