A PARTIAL LOSS OF CABIN PRESSURIZATION LED AN ACR FLC TO DIVERT.

Narrative

ACR FLT FROM SJC TO SNA. CLRED TO DEPART RWY 12; MOONY 1 DEP TO AVE; MAINTAIN FL230. DEP WX 5 SCATTERED; 32 OVCST 7R - DEST WX W2 OVCST 3F. OUT OF 10000 FT CLRED TO MAINTAIN 15000 FT; DUE TO HIGHER TFC FOLLOWING US (CONFIRMED WITH TCASII). SUBSEQUENTLY STEP CLBED IN 1000- 3000 FT INCREMENTS. ENCOUNTERED HVY PRECIPITATION IN CLB; HOWEVER; NO ICING. APCHING AVE WE WERE RERTED OVER FIM TO MAINTAIN FL290. OUT OF FL260 NOTED CABIN ALT WARNING LIGHT. LEVELOFF REQUESTED AND NOTED 11000 FT CABIN ALT. REQUESTED LOWER ALT AND WAS CLRED TO FL200. CABIN ALT DID NOT RESPOND TO CORRECTIVE PROCS AND CABIN ALT SLOWLY INCREASED. REQUESTED FURTHER DSCNT. AS DSCNT INITIATED TO 11000 FT OXYGEN MASKS DEPLOYED. FLT ATTENDANTS ASSISTED THOSE PAX HAVING DISCOMFORT TO DON MASKS. NO PANIC. ATTEMPTS TO CONTACT ARINC ON 130.8 SEVERAL TIMES THROUGHOUT PRECEDING EVENTS WERE NEGATIVE. NOTIFIED ATC OF REQUEST TO DIVERT TO LAX. APCH AND LNDG AT LAX UNEVENTFUL AND NO PAX COMPLICATIONS NOTED. DID NOT DECLARE AN EMER DUE TO GRADUAL LOSS OF PRESSURE DURING CTLED DSCNT.