What was found
(CAN) AS THE AIRCRAFT CLIMBED THROUGH 14,000 FT, CABIN WOULD START CLIMBING AT THE RATE OF 1000 FT PER MIN AT 20,500 FEET, IT WOULD START WORKING PROPERLY. ON INSPECTING THE VENTURI, IT WAS NOTED THAT BOTH LINES THAT GO FROM THE VENTURI TO THE TEST PORTS IN THE AISLE WAS FOUND BOTH BURNED OFF OVER AS PERIOD OF TIME. NEW HOSES WERE INSTALLED AND TESTED AND FOUND TO BE THE PROBLEM.