Abstract: A portable air compressor unit includes a sound attenuating enclosure formed to have a first compartment through which cooling air flows before passing through side-by-side mounted heat exchangers for engine coolant and compressor injection liquid. Engine and compressor inlet air filters are disposed in the first compartment. An engine driven fan draws cooling air from the first compartment into a second compartment containing the engine and compressor. An engine inlet air silencer and exhaust gas muffler are also disposed in the second compartment. Heated cooling air is discharged from the second compartment into three side-by-side ducts at the end of the enclosure opposite the first compartment. Exhaust openings in the end and side walls of the enclosure provide for final exit of the cooling air from the enclosure above the level at which cooling air enters the first compartment.