4406 Aprilaire float assembly. Features. For use with Aprilaire models 400 400a 400M and 600. two float assemblies required; one for function and one for safety backup. these float in the scale control insert float chamber to control the supply of water. when the water level is high enough the right hand float turns off the water supply. as water evaporates and the float reaches the bottom the electronic switch is activated and the water supply turns on.