the new compressors dont apply much load, e.g. the old harrison A6 compressors (iron monsters) can sap quite a lot of power from the engine, or the old york upright 2 piston compressors load up the engine like murder, The newer scroll type are very efficient and lightweight too.
Explaining the required torque to turn the crankshaft or wobble plate or scroll drive of the compressor is quite boring.