GPD Multiplexer for HVAC and Pump Applications The MagneTek GPD Multiplexer System allows one VFD drive to perform the function of several VFDs in multi-motor HVAC and pumping systems. Operation The GPD Multiplexer utilizes one GPD 506 VFD, with horsepower rated for the largest motor, and sequentially controls all the motors to achieve infinitely variable response to system demand. MagneTek has developed the unique and reliable method of transferring motors back and forth betwe...