Simply disconnectng the power to the engagement clutch will stop the pump from feeding air to the head, BUT, the ECU also sends an electrical signal to the Switch-Over-Valve that supplies vacuum to the the AIR valve between the pump and the head AIR ports. [ this feed signal is in parallel with the clutch power feed and are the same ].

Unplugging clutch for non AIR system operation also requires SOV dis-connect and/or SOV/AIR valve vac line plug/BBing......