1–12 DURING TROUBLESHOOTING (cont)

TM 1-1520-238-T-4 1–8 1–12 DURING TROUBLESHOOTING (cont) 1–12 CAUTION Ensure the environmental control system (ECS) fans are operating while electrical power is applied to the helicopter to prevent equipment damage. b. ALWAYS maintain required cooling of units while operating equipment. NOTE For information on cooling requirements, refer to the ECS in TM 1-1520-238-T-8. c. If troubleshooting procedures indicate that a LRU is faulty, it is replaced a second time only under one of the following conditions: (1) When a pre–existing failure in the interconnecting wiring or system caused the newly replaced LRU to fail and the pre–existing failure has been corrected. (2) The replacement LRU is known to be defective and the interconnecting wiring is known to be good. d. The LRU is not to be replaced under any of the following conditions: (1) If the interconnecting wiring is not known to be OK. (2) If the newly replaced LRU is not known to be defective. (3) If under any circumstances the LRU has already been replaced a second time. 1–13. COMPLETING TROUBLESHOOTING 1–13 a. Prior to application of power ensure the following: (1) Attach items detached during troubleshooting. (2) Reinstall or replace items removed during troubleshooting. b. To ensure that trouble is corrected, repeat the MOC. c. Secure all doors, panels, and opened areas. 1–14. GENERAL PROCEDURES – SUMMARY 1–14 a. Use only correct methods and checks (para 1–5). b. Use the troubleshooting data like a road map (fig. 1–3). (1) You MUST start at the beginning and follow to the end. (2) Do not skip or miss a step. (3) In flow diagrams, ALWAYS start with the upper left block.