Peterbilt Medium Duty Trucks Operator's Manual after 1-07

Preventive Maintenance
head. Also, check compressor discharge line for carbon,
and clean or replace the discharge line if necessary.
• Disassemble compressor and thoroughly clean and
inspect all parts. Repair or replace all worn or damaged
parts, or replace compressor with a factory exchange
unit.
CAUTION: When draining the engine cooling
system is required, to prevent damage from
freezing, the compressor must also be drained
at the cylinder head and block. Engine damage
could occur if the cooling system is not periodically
drained and maintained. See “Engine Cooling
System,” Page 143, and the Medium Duty
Maintenance Manual for further information.
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 Bendix
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
Air System
tank, and rear dry tank. The dry tanks have a single-check
valve in the tank inlet. The check valves prevent a complete
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
reason to replace a desiccant cartridge; oil-stained
desiccant can function adequately.
Every 900 operating hours or 25,000 miles/40,000 km or 3
months, check for moisture in the air brake system by opening
reservoirs, drain cocks, or valves and checking for the
presence of water. A tablespoon of water in a reservoir 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 highway
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 normal fashion or it
may be due to excessive leaks in the air system.
Medium Duty (R10/06) Y53-6008 – 165 –