What was found
DUE TO EXTENSIVE HISTORY OF "NO" OR "LOW" DUCT PRESS AND PREVIOUS PARTS CHANGES TECH SERVICE REQUEST THE FOLLOWING BE ACCOMPLISHED. GROUNDED - YES. REMOVED AND REPLACED SURGE CONTROL VALVE IAW B737-800 AMM 49-52-41. PERFORMED SURGE CONTROL VALVE INSTALLATION TEST. OPS CHECK GOOD, NO DEFECTS OR LEAKS NOTED. ACCOMPLISHED STEP 1 AND STEP 2. PERFORMED APU BITE, REF B737-800 FIM 49-61-00-700-801. NO CURRENT FAULTS FOUND. REMOVED AND INSTALLED NEW APU HARNESS, REF B737-800 AMM 49-11-01-000-802 AND 49-11-01-400-802. ACCOMPLISHED APU OPS TESTS PER SAME. ALL TESTS PASSED.