Orifice controlled bypass system for a high pressure air compressor system

An apparatus for supplying compressed air to air operated elements of a locomotive includes an air compressor, an aftercooler coupled for receiving compressed air from the compressor, a cooling fan for blowing ambient air onto the aftercooler for reducing the temperature of the compressed air, whereby moisture in the compressed air forms condensation which is discharged from the compressor during normal operation of the aftercooler. A bypass system shunts the compressed air from the compressor around the aftercooler when the condensation freezes in the aftercooler passages and blocks normal air flow. The bypass system includes an orifice of a size selected to create a pressure drop which is greater than a pressure drop across the aftercooler when air flow through the aftercooler is not inhibited by blockage whereby air flow from the compressor normally passes through the aftercooler and bypasses the bypass system.