Soft start compressor clutch

An electromagnetic clutch (10) for an air conditioning compressor includes a generally cylindrical pulley (11) rotatably mounted on a comressor housing (16) and having an annular friction surface (21b), a driven member (12) mounted on a compressor shaft (13)and having an annular friction surface (21a) positioned radially adjacent the first friction surface to form an annular space (21c) therebetween. A quantity of flowable magnetic material (27) is provided in the annular space (21c) and a magnetic coil (34) is fixed on the housing adjacent thereto. A control (40,46,46') connected to the magnetic coil (34) supplies electrical power from a power supply (47) to energize the magnetic coil and create magnetic flux in the annular space (21c) polarizing the magnetic material and frictionally coupling the first and second friction surfaces (21a,21b) to cause the pulley (11) to rotate the driven member (12). The control (40,46,46') can pulse width modulate or ramp the supplied power for "soft" starting and/or stopping of the compressor.