What was found
ON DESCENT PRESSURIZATION CONTROL "AUTO FAIL LIGHT" ILLUMINATED COMPLIED WITH QRH PROCEDURE, SELECTED ALT MODE. "AUTO FAIL LIGHT" EXTINGUISHED. GROUNDED - YES. CPC1 HAS ACTIVE OUTFLOW VALVE LRU FAIL FAULT. OUTFLOW VALVE OPERATES NORMALLY WITH SWITCH IN ALTERNATE AND MANUAL. SWAPPED CPC 1 AND CPC 2, FAULT FOLLOWS CPC. REINSTALLED CPC 2, REMOVED AND REPLACED CPC 1 REF B737-800 AMM 21-31-00-700-802. OP CHECK FAILS, CPC 1 STILL LOGS 009 OUTFLOW LRU FAULT INTERMITTENTLY. REMOVED AND REPLACED OUTFLOW VALVE REF AMM 21-31-03/401. PERFORMED PRESSURIZATION SYSTEM TEST REF AMM 31-31-00-700-802 AND PRESSURIZATION SYSTEM MANUAL MODE TEST REF AMM 21-31-00-710-801. NO FAULTS FOUND, OP CHECKS GOOD.