MD Central Vacuum Circuit Board, 120V, Fits AirMaster, Flo-Master, APX

MD Manufacturing built several single-motor power unit lines on the same 120-volt control platform, and this board is the low-voltage brain behind that platform, watching for a signal from a wall switch plate or a remote keypad press and switching the motor circuit on and off. It is labeled for the AirMaster, Flo-Master, and APX lines.

A no-start unit, one that runs nonstop, or one that has stopped answering the wall inlets is usually a control board problem rather than a motor problem, and replacing the board costs a fraction of a new power unit. Because the board carries both the low-voltage sensing circuit and the relay or triac that switches the motor, a single failed component on the board can produce any of those three symptoms depending on where the fault sits.

This 120V board is built for single-motor units drawing up to 18 amps; dual-motor and higher-current MD units use a different board entirely, so confirm the voltage and amperage stamped on your unit's data plate before ordering rather than going by model name alone. MD's single-motor lineup has carried this control platform across more than one model name over the years.

Beyond AirMaster, Flo-Master, and APX, check the board layout and connector count against your original part before installing, since later or higher-output revisions in the same family can use a different board even when the outer housing looks identical.

• Part: 235S18
• Fits: MD AirMaster, Flo-Master, APX (120V single-motor, 18 amp)
• Job: low-voltage control that starts and stops the motor from an inlet or a remote
• Not for: dual-motor or higher-current MD units on a different board