guide vanes in response to an input signal from a central processing unit cpu 23 under most operating conditions where the system is being used in moderate climates the guide vanes will exercise sufficient control over the compressor so that the machine will not surge when operating at a low capacity however this is not the case when the system is forced to operate in climates where ambient wet bulb temperatures remain relatively constant as noted above the present compressor is equipped with a recirculating diffuser which serves to maintain the flow through the diffuser relatively constant despite changes in load demands the fluid flow leaving the impeller is directed into a pipe diffuser section generally referenced 26 this type of pipe diffuser is described in greater detail in u s pat no 5 445 496 owned by the current assignee which was filed in the name of joost brasz and the disclosure in the brasz patent is incorporated herein by reference as illustrated in fig4 the pipe diffuser is formed of a single annular casting 27 which is supported upon the shroud 28 of the compressor the casting as shown in fig3 overlies the exit region of the impeller and extends radially to the rim of a collector chamber 29 a plurality of circumferentially spaced diffuser channels 30 30 are formed in the casing so that the centerlines 31 31 of the diffuser channels are tangent with a common circle 32 which in this case describes the inner rim of the casing each channel has three axially aligned cojoined sections 34 36 the first section 34 is cylindrical.