As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT NOTICED A LOW VAC WARNING OF THE ENGINE DRIVEN VACCUME PUMP. TURN THE SWITCH ON FOR THE STANDBY VAC SYS AND THE CIRCUIT BREAKER POPPED. FOUND THE CAUSE OF THE STANDBY VAC PUMP CIRCUIT BREAKER POPPING WAS A FROZEN VAC PUMP. INVESTIGATION REVEALED THAT THE SUPPLY HOSE, THAT IS MADE OF RUBBER WAS BREAKING DOWN INSIDE AND FILLING THE PUMP UP WITH CONTAMINANTS.