The Aprilaire 4740 is the correct replacement for the Aprilaire Model 700A Humidifier
& Aprilaire Model 700M Humidifier.
The Aprilaire 4740 Humidifier Fan Relay is a replacement relay that powers up the circulator fan in the latest Aprilaire 700 model, 700A and 700M humidifiers since 2008. Newer versions of the 700 model series use an external transformer to power the control circuit, along with the Aprilaire Fan Relay. The tools you will need for installing your fan relay are a Phillips screwdriver and a pair of needle-nose pliers.