What was found
LH PACK HI TEMP MSG POPPED UP AND DISAPPEARED FROM CAS CLIMBING THROUGH FL180. CA CHECKED ECS PAGE AND NOTICED LEFT PACK WAS NO LONGER BEING SUPPLIED 10TH STAGE BLEED AIR. WE LEVELED OFF CABIN ALT CAUTION MESSAGE POPPED UP AND CA NOTICED CABIN ALT SLOWLY CLIMBING. STARTED THE QRH PROCEDURE. (FLIGHT 5956 - FILED CLOSED) REMOVED AND REPLACED LH ACM IN REFERENCE TO AMM 21-51-10. PERFORMED OPS CHECK OF LH AIR-CONDITIONING PACK, OPS CHECK AND LEAK GOOD. PRESSURIZED AIRCRAFT, PRESSURIZATION OPERATED NORMAL. PLEASE REFERENCE AML 1618974