What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: RECEIVED CABIN ALTITUDE ALERT AND MASKS WERE DEPLOYED; AIRCRAFT AIR INTERRUPTED BACK TO AND LANDED SAFELY AT MEX. PERFORMED DIGITAL CABIN PRESSURE CONTROLLER (DCPC) BITE PROCEDURE AT NO. 1 AND NO.2 DCPC PER FIM 21-31-00-810-801, NO FAULT FOUND AT THE MOMENT, THEREFORE PERFORMED PACK AND ZONE TEMPERATURE CONTROLLER BITE TEST TO THE LEFT AND THE RIGHT CONTROLLERS PER AMM 21-61-00-700-806-002. NO FAULT FOUND BOTH SYSTEMS OK FOR SERVICE.