Air systems: Solution
While most think of summer as the humid time
of year in northern climates and winter as bone
dry, there is actually a relatively high amount of
moisture in the air when it’s cold.
“Even in winter, there’s still humidity in the air
that gets pulled in through the air compressor and
then goes into the service tanks,” Nagel says. “Th e
air dryer’s job is to remove that moisture.”
Th e air dryer is located between the air
compressor and the rest of the air system. It uses
replaceable cartridges containing desiccant material,
which attracts and traps moisture before it
can reach the rest of the system. Periodically, the
system backfl ushes air through the air dryer to
clear moisture from the desiccant and vent it to
the outside.
Nagel explains that by design, mechanical air
compressors pass minute amounts of oil. So, in
addition to preventing moisture from passing
into the air system, the air dryer has to fi lter
oil aerosols as well. Th is eventually leads to
decreased performance.
“Th e desiccant itself doesn’t really wear out, but
over time it gets contaminated with oil aerosols,
and it becomes less eff ective,” Nagel says. “When
the dryer desiccant gets contaminated, it doesn’t
remove all the moisture in the system. Th at moisture
goes into the service tanks and eventually
into the brake system, sits around at low points in
the brake system and freezes in winter.”
Th e easiest way to prevent this from happening
is by including air dryer inspection and service
as part of a fl eet’s regular PM program.
“An important preventative measure is ensuring
proper care of the air system with year-round
maintenance of the air cartridge,” Hale says.
“Moisture and contaminants that make it into the
14 Fleet Maintenance | October 2018
air system past an improper or defective cartridge
during warmer months will not be removed by
replacing the air cartridge in October. It is important
to inspect and maintain the air dryer and
cartridge throughout the entire year.”
Most OEs and air system manufacturers
publish recommended replacement intervals
for desiccant cartridges. Bendix, for example,
recommends replacement every three years for
standard air usage applications such as line haul
and city delivery; every two years for medium
air usage applications such as double trailer
trains, light transit and light off -highway; and
every year for high air usage applications such
as multiple trailer trains, city transit and heavy
off -highway.
Nagel adds that location can also play a factor in
replacement intervals, and that operating in colder
climates can put additional stress on air systems.
Th e bottom line is that fl eets should visually
inspect the air tanks to see if the air dryer is operating
correctly. If excessive moisture is present, more
frequent cartridge replacement may be necessary.
Hale adds that if moisture has collected in the
» Checking battery cables for signs of loose
or corroded connections is important, but
the state of the battery itself should also
be tested to get an idea of the condition.
Photo courtesy of TravelCenters of America
air tanks, it must be drained. Once the water has
drained, the plugs should be left out long enough
for the tanks to dry out completely.
Fleets should also be cautious about the
replacement cartridges used. While aft ermarket
parts may off er lower pricing, the desiccant
inside may not be the same quality as an OE part,
and therefore require more frequent replacement
or even cause issues that could have otherwise
been avoided.
Other maintenance items on air dryer systems
include replacing the purge valve, which road salt
and other debris can clog, especially aft er a hard
or particularly long winter. Another part that is
relatively inexpensive and easy to change is the
air dryer heater. Th is part is imperative to keep
the air system working in freezing temperatures,
and there is no indicator as to whether or not the
heater is working, so replacing it periodically is
the only way to ensure proper function.
Electrical systems
Like the air system, a vehicle’s electrical system
can be dramatically impacted by winter weather.
Battery life can suff er in the cold, leading to
alternator trouble or even starting issues. Plus,
salts and chemicals used to melt ice on roadways
can cause corrosion in wiring harnesses, leading
to poor electrical connections. To prevent this
from happening, fl eets should take preventative
measures before winter weather sets in.
An important
preventative
measure is yearround
maintenance
of the air cartridge.
Continued Page 18