What was found
CLIMBOUT, HAD LESS THAN 2 PSID AT 10,000 MGL, LT AIR MIX VALVE WOULD NOT WORK, LT PACK WOULD NOT PRODUCE ANY AIR FOR PRESSURIZATION ON ENG 1 OR 2 BLEED. PRESSURIZED ACFT USING BOTH PACKS, EQUIPMENT COOLING AIR SHUTOFF VALVE DID NOT CLOSE BY 3 PSID. WRENCHED VALVE CLOSED AND PRESSURIZED ACFT TO 6.5 PSID USING GROUND AIR SOURCE. REPLACED COOLING AIR VALVE IAW MM 21-58-021-4. PRESSURIZED ACFT USING ENGINE BLEEDS 1 & 3 TO 7.5 PSID. ACFT MAINTAINED CURRENT CABIN ALTITUDE WITH 1 & 3 ENGINES AT IDLE AND SUPPLYING PNEUMATICS. BOTH PACK MIX VALVES WORKED NORMALLY DURING TEST. REPLACED LT FWD PACK SHUTOFF VALVE IAW MM 21-55-071-4, REQUIRES OPS AND LEAK CHECK.