What was found
LEVEL AT FL340 GOT A CABIN ALT WARNING. CABIN ALTITUDE WAS JUST ABOVE 10,00 FT. STARTED AN EMERGENCY DESCENT. WHILE IN DESCENT GOT CABIN ALT AUTO 1 INOPERATIVE MESSAGE. SWITCH TO AUTO 2 CONTROLLER AND CABIN ALTITUDE RETURNED TO NORMAL. BITE NR 1 CPC FOUND AC MOTOR FAULT. REPLACE NR 1 AUTO M2 AC MOTOR AND OPERATIONS CHECKS GOOD IAW MM21-31-05-4-0. NEW PART INSTALLED, AC MOTOR MFG PN 20222478-5 AND SN 9454. REMOVED PART AC MOTOR MFG PN 2022478-4 AND SN 109-2316. AWAITING ERS FOR PART COMPATIBILITY ISSUE ERS 20-01872. IAW ERS 20-01872 OK TO CONTINUE WITH PARTS INFO.