Ed, there are 3 ways the Air compressor will gets sourse of air from. Number 1 from a air filter on
air compressor housing itself. Number 2 from pipe connected into air filter and engine turbo charger.
Number 3 air compressor gets air supply from intake manifold on engine via of 1 inch hose. while
on subject I have seen all three systems on motorhomes, There seems to be no standard when builder
puts house over the motor. Again answer to your question, It may not be the same for others as yours.
The engine S/N number plays a big part in where you going with this. Different S/N will change how
add-ons location will be different from engine to engine. Mounting of the fuel filter is a good example
to play with. Cat C-9 engine the air governor is remote from air compressor to upright support on
right side of engine in back . Engine Data Connector another good example, some models along inside
of right frame rail to above rear back of engine. last the big air filter it self, different locations mean
different mounting of add-ons. I answered your three fold as way Cat SIS lays out info for many different
locations of add-on . again there is not one standard set in stone. Dave Atherton Retired Cat Mechanic