A failure analysis approach to solving refrigerant connector failures in rail coach air conditioning units

Abstract

Investigation of failures in connectors of compressor suction and discharge lines in roof mounted package air conditioners designed for use in passenger coaches of Indian Railways was the objective of the study. The connectors consisted of copper pipe and corrugated red brass flexible tubing reinforced with bronze wire braiding. Resonance between the discharge line and the first harmonic of the compressor excitation frequency was the cause of failure in this line. In the suction line resonance was ruled out as a reason of failure. Tests conducted on the compressor connector subassembly to simulate shocks encountered during coach movement could replicate field failures. A change in the compressor mounting from soft to rigid resulted in elimination of the failures in these simulated tests. So shock was concluded as a reason for suction line failures and a change in mounting of the compressor has been recommended as a solution to prevent failures. The connectors have been changed to plain copper tubes with a geometry tested for absence of resonance with compressor excitation frequencies.