I recently put a Moist-n-Aire unit into a new humidor build, and it's been a bit of love/hate with the humidifier. The Moist-n-Aire is so simple, effective, and easy to use that it's almost dummy proof, but I've had two big problems! Since I've now fixed them both, I wanted to share with anyone else who uses a Moist-n-Aire.
First, the unit has a big cork and bobber thing that shows the water level -- low tech but effective. The cork though is natural material, and no matter how much I cleaned it, it led to moldy gunk floating around in the water. I replaced the natural cork with a synthetic one from a wine bottle, and problem solved.
My second problem was bigger. The humidity controller is a Ranco unit designed for household systems, and it's terribly inaccurate for this purpose (especially with a brute like the Moist-n-Aire). It's advertised with a differential of either 5 or 15% RH, but I couldn't find any way to adjust it or switch between the two levels. It either ran way too much or not at all. My fix was to completely remove the Ranco unit and then connect the wires so it was set to run all the time. I bought a digital humidity controller (Inkbird IHC200; $42 on Amazon) and plugged the Moist-n-Aire into this. I can set the upper humidity limit, and a differential to within 1%. The new controller also has a second plug for a dehumidifer if you need that. The controller is hidden under the cabinet, but with a sensor on a 6 ft line to place inside (haven't mounted it yet).
Here are pics, before and after.