YOUR VEHICLE’S AIR SYSTEM PART 8: MAINTENANCE AND SERVICE
– 170 – Y53-6007 (R10/06)
Air Dryer
WARNING! Use of incorrect air dryer could
cause air system failure, leading to loss of
vehicle control and serious personal injury or
death. If your vehicle is equipped with a Ben
-
dix AD-IS air dryer, it is important that future
replacements be identical or similar in design.
Any deviation from the Bendix AD-IS type air dryer would
require changes to the vehicle air system. Some vehicles
use a dual air system consisting of a wet tank, forward dry
tank, and rear dry tank. The dry tanks have a single-check
valve in the tank inlet. The check valves prevent a com
-
plete loss of air in the event of an air system failure (tank
or hose failure). This ensures a controlled stop (with
reduced braking capability). Other vehicles use a Bendix
AD-IS air dryer which eliminates the need for a wet tank
and check valves in the dry tanks.
NOTE: A small amount of oil in the system may be
normal and should not, by itself, be considered rea-
son to replace a desiccant cartridge; oil-stained
desiccant can function adequately.
Every 900 operating hours or 30,000 miles/48,000 km or 3
months, check for moisture in the air brake system by
opening reservoirs, drain valves, or valves and checking
for the presence of water. A tablespoon of water in a res
-
ervoir would point to the need for a desiccant cartridge
change. However, the following should be considered first:
• Air usage is exceptionally high/abnormal for a high-
way vehicle. This may be due to accessory air
demands or some other unusual air requirement that
doesn’t allow the compressor to load/unload in a nor
-
mal fashion or it may be due to excessive leaks in the
air system.
• When more than a 30-degree F (17-degree C) range
of temperature occurs in one day, small amounts of
water can accumulate in the air brake system due to
condensation. Under these conditions, the presence
of small amounts of moisture is normal and should not
be considered as an indication that the dryer is not
performing properly.
• An outside air source may have been used to charge
the air system, in which case this air did not pass
through the drying bed.
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