Aprilaire 550 doesn't seem to be getting power

Hello, if there is not voltage at the HUM and Neutral terminals when the blower energizes than the portion of the board is bad that controls the humidifier, but you can get around that by just adding a transformer and a current sensing relay.

Hello, apply power directly from transformer to solenoid valve, it it does not turn on the solenoid valve must be replaced. If there is no voltage to the solenoid then follow the wires back and see where there is no voltage.

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.

Hello, check to see if you are getting 24 volts to the solenoid valve, if you are and it does not click on to let the water into the humidifier then the solenoid must be replaced. However if you are not getting 24 volts to the solenoid valve check if yuou are getting 24 volts at the transformer, if not then turn power off to transformer and check the continuity of the secondary side of the transfomer, you should have resistance if not replace the transformer. if that checks out good check the wire connection between transformer and solenoid and make sure it is tight. If wire connection looks good then either humidistat is bad or current sensing relay/sail switch.

Hello, make sure you are getting 24 volts at the transformer, if not turn off power to transformer and check resistance on the secondary side of transformer, you should have resistance if not replace transformer. If you have 24 volts at transformer than check the wiring and make sure it is tight. the last thing to check is to make sure you are getting 24 volts in and out of the humidistat. if you are not replace humidistat.

The first thing to check is if you are getting 24 volts at the transformer, if you are not then turn off power the transformer and check continuity. u should have continuity if not replace the transformer. If you are getting 24 volts at the transformer then apply 24 volts directly from transfomer to solenoid valve you should hear the solenoid cleck open and let the water in, if not then the solenoid is bad and must be replaced. If the solenoid does work by applying voltage directly to it then check the
wiring and make sure it;s all tight. Also check the humidistat and current sensing relay/sail switch to make sure it's functioning properly.

If you are not getting voltage to the solenoid valve then start at the transformer and check if you are getting 24 volts. If not then turn off power to the transformer and set your meter to continuity and check the transformer, if you dont have continuity the transformer is bad and must be replaced. If the transformer is good then check the wring to make sure the connections are tight and the humidistat, if that check out good then the current sensing relay/ sail switch is bad.

Hello, it depends on what type of setup you have with your humidifier. If you have a current sensing relay or sail switch than that wire connects there, howevere, if you have the humidifier that is powered by a furnace control board than that wire will connect to the transformer that the control board is providing with 120 volts with.

This sounds like, the 550 transformer is not connected to the blower motor power connection (in parallel)

I just solved a problem with mine today.  One of my low voltage power wires to the humidity control had a bad connection.  I reconnected it and I could again hear the solenoid valve clicking as I adjusted the dial control.
I found the problem with a voltmeter:  there was voltage at the power terminals on the humidity control terminal board, but there was no voltage at the solenoid valve terminals.  It was hard to push my big wires into the terminal board, but I finally secured the connection!