What was found
AT 21,000 FT, CABIN VSI SHOWED 2,000FT/MIN CLIMB WITH A LARGE RUSH OF AIR, SAME THING HAPPENED AT 15,000, PRESSURIZATION STABILIZED AT 9,000. MX FOUND THE SAFETY VALVE FILTER WAS PLUGGED WITH DUST AND LINT. SQUAT SWITCH THAT CONTROLS THE SAFETY DUMP VALVE WAS REPLACED DUE INTERMITTENT CONTACTS. PRESSURIZATION TESTS WERE CARRIED OUT AND NO FURTHER ISSUES WERE NOTED.