What was found
PHX - AIR TURNBACK - FLT 536 - ABOUT 10 MIN AFTER DEPARTURE FROM PHX EN ROUTE TO CLE THE BLUE HYD SYS PRESS AND QUANTITY DROPPED TO ZERO AND ASSOCIATED WARNING INDICATIONS WERE DISPLAYED. THE AIRCRAFT RETURNED TO PHX MAKING AN UNEVENTFUL LANDING. MAINTENANCE INSPECTED THE AIRCRAFT AND FOUND THE BLUE HYD SYS ELEC MOTOR DRIVEN HYD PUMP LEAKING FLUID AT THE PARTING SURFACE BETWEEN THE MOTOR AND PUMP. THE MOTOR/PUMP ASSY WAS REPLACED, THE SYSTEM SERVICED AND ALL FUNCTIONAL AND LEAK CHECKS WERE GOOD.