a compressor 34 an expansion valve 36 and a reversing valve 38 see fig3 according to a key aspect of the present invention an opening 40 uniquely providing a combination of both horizontal and vertical access to the interior of the chassis 12 and the components therein is formed through a side wall portion of the chassis 12 preferably the access opening 40 is disposed in a vertical corner portion of the chassis 12 between adjacent vertical edges 20 a 22 a of the chassis side walls 20 22 which are horizontally foreshortened relative to the other two side walls 24 and 26 access opening 40 in addition to its vertically extending side portion has an open top end 40 a see fig3 which is normally covered by a removable corner portion 16 a of the top side wall 16 see fig1 and 2 condenser coil 30 has a horizontal peripheral gap 41 which is aligned with and defines an inward extension of the vertical side portion of the chassis access opening 41 with the condensing unit 10 in its fig1 fully assembled state the open top end 40 a of the access opening or passage 40 is covered by the installed top side wall corner portion 16 a of the top side wall 16 and the outer side of the opening 40 is covered by a control box bracket structure 42 which is suitably and removably secured to the opposite side wall edges 20 and 22 a and is positioned horizontally inwardly of liquid and suction valve portions 44 46 of the overall refrigerant circuit as may be best seen in fig2 the control box bracket structure 42 has a vertical panel portion 48 with a horizontal shelf projecting horizontally outwardly therefrom mounted on the outer.