During the normal operation of an Aprilaire home humidifier, the unit opens a water valve, operated by a special electrical device, called a solenoid. When the unit needs water, it sends an electrical impulse to the solenoid, magnetizing a coil in the device. The magnet then pulls the valve back, magnetically, to allow the water to flow. If the solenoid fails, the water will not flow, providing too little moisture in the home. The solenoid is self-contained. It requires replacement to service and repair it.
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Unplug the humidifier unit, if possible. Turn off the breaker to the unit. Turn off the water supply to the unit.
Disconnect the water line from the solenoid valve by turning the inlet and outlet compression nuts counterclockwise with the adjustable wrench. Slide the compression nuts away from the solenoid valve. Remove the inline strainer in the inlet and the orifice in the outlet of the solenoid valve.
Take note of the positive and negative wiring on the solenoid valve. Disconnect the wire nuts on the wiring and remove the solenoid valve wires from the humidifier wires. Unscrew the mounting bolt from the solenoid valve with the Phillips head screwdriver and remove the valve.
Position the new solenoid valve in the humidifier. Attach the mounting bolt to secure the valve in place. Rewire the valve to the humidifier, and replace the wire nuts on the ends of the wires.
Insert the inline strainer into the inlet and the orifice into the outlet in the new solenoid valve. Reattach the inlet and outlet compression nuts.
Turn the water supply on. Check for any leaks and readjust the compression nuts, as necessary. Wipe any water from the unit with a towel.
Turn the breaker to the humidifier back on. Plug it in, if necessary.
Turn the control dial on the humidifier to the "Off" setting. Turn the dial clockwise, slowly, until you hear the solenoid valve click open. Check for water to flow into the unit. Turn the dial back, slowly, until you hear the solenoid valve click off. Check for the water flow to cease. The unit is now ready to configure for your home.