Solenoid on Aprilaire whole house humidifier

Some helpful videos in the link as well as text articles and a link to a previously answered question on Fixya.

https://www.google.com/search?q=Aprilaire+760+making+strange+sound

It may be too high a water pressure for the solenoid.

Aprilaire Humidifier, too powerful a solenoid? Vent ducts noise.

https://www.houzz.com > discussions > aprilaire-humidifie...
The noise might be caused by having the water pressure up too high for the solenoid. Try backing off the water supply until the sound goes away. Hopefully, ...
..

Hello, are you getting 24 volts to the solenoid vlave? If you are and the solenoid does not open it must be replaced, the 24 volts opens the solenoid and also energizes a small relay to turn on the fan. If you are not getting 24 volts to the solenoid valve then start at the transformer and work you way toward the solenoid and see where the voltage stops.

The first thing you want to check is that the saddle valve is open and that water is getting to the solenoid. If you are getting water to the solenoid but it's not going through then most likely you are not getting power to the solenoid. When there is a call for heat you should be getting 24 volts to the solenoid and it will open allowing water into the humidifier, if you are not getting 24 volts then check the transformer make sure it is giving you 24 volts.

Hello,Make sure the heating blower/fan is running when you turn the dial as the humidifier might not have power if there is no heating blower operation.

Hope this solves your problem, look for the humidistat, it should be located on cold air return duct near furnace, make sure it is not set in the on position, if it is, then this is why it is staying on, please set humidistat any where from 20 to 35%, never over 40%. If the humidistat is set properly and is still running, you may have a electrical problem, humidifier circuit should only receive power(24 volts) when the indoor blower motor of furnace receives power, also if you have galvanized plumbing in your home, you may have a piece of rust or lime deposit in the humidifier solenoid valve preventing it from closing, turn water off to humidifier and disconnect water supply line entering solenoid valve inspect & clean protector screen. Good luck.

A simple check you can perform on your aprilaire 760 is the following:
1) locate the two brown wires coming out of the 760 (these wires will be wired to tell the 760 to turn on when the hvac bower is on and the humidistat is calling for moisture).
2) temprarily disconnect the two brown wires from the external wiring and then short the wires together. All you're doing here is bypassing the your thermostat and bower-on indicator.

With the 70 unit plugged in to the wall outlet and the two brown wires connected together, both the fan and the solenoid valve (water inlet valve) should both be activated.

check to see if you have 24 volts between to 2 yellow wires coming out of the water solenoid. if you have 24v, then it is still getting energized to run. if it does not have 24v and the water is still running, the solenoid is stuck open. most likely from water deposits. sometimes you can take the solenoid apart and clean it, but probably better off just getting a new solenoid.

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.

Sounds to me like the solenoid valve is your problem and it is likely stuck due to sediment. I beleive Aprilaire has superceeded all of their old valves to the part number 4040 (used on all models of aprilaire humidifiers) - anyone who services these units regularly likely has one in stock usually $60 - 100.

You need to determine whether the problem is in the solenoid or in the furnace electronics. You could put a voltmeter on the solenoid connection to see if the furnace is still holding the solenoid open after the blower stops. This will tell you whether it is the solenoid or not.