Compressor pre-spin control method

A compressor (11) is connected via a clutch (13) to a crankshaft of an internal combustion engine provided with a turbocharger (12). A compressor pre-spin operation is used to reduce the transferred energy and wear when the clutch is engaged. The pre-spin is achieved by controlling the air mass flow over the compressor, wherein the air mass flow over the compressor is controlled by controlling a bypass throttle angle of a bypass throttle (18) provided in a bypass conduit (17) bypassing the compressor.