ATA 21

1124 Air Cycle Machine Failure Prevention Maintenance
The 1124/1124A environmental system air cycle machine (ACM) is maintained in an "on condition" basis by regular oil changes. normal service life of an ACM can exceed 2000 flight hours when all cooling system components are functioning properly to protect the machine from overspeeds or icing conditions.

If an ACM failure does occur, the operator should perform the "Post Cooling Turbine Failure Inspection" detailed in the 1124 AMM 21-50-00. These procedures include a thorough visual inspection of the ram air ducts and check of the fluid pressure regulator valve.

Along with the components checked in the procedure noted above, a dirty heat exchanger can contribute or cause a shortened ACM life. The AMM also includes an approved "Heat Exchanger Inspection and Cleaning Procedure" in chapter 21-50-00. If your heat exchanger has never been cleaned, this procedure should be considered during a ACM replacement, or as a preventative ,maintenance step at the operator's option.

There are some older Service Information Letter and Service Bulletins that have been issued that detail various system upgrades and maintenance tips. A review if these documents and their application may help prevent a future ACM failure in your aircraft.