lower levels of maintenance because of the high
cost of special equipment required for making
adjustments necessary to proper operation.
In most instances, a maladjusted or mal-
functioning component must simply be removed
and replaced. There are, however, certain
components that require periodic servicing,
cleaning, and inspection so the component will
function properly and efficiently and may be
considered reliable for flight. Specific require-
ments for servicing, cleaning and inspection are
listed in the daily, postflight, and special/
conditional, Maintenance Requirements Card
(MRC) decks as well as the MIM for each aircraft.
Electrical Failures
Since all pressurization and ACSs have
electrically controlled components, maintenance
of these systems must include the related electrical
circuits. Although an AE is generally called upon
to locate and correct electrical troubles, the AME
should be able to check circuits for loose
connections, and even perform continuity checks
when necessary. A knowledge of electrical
symbols and the ability to read circuit diagrams
is therefore necessary. Figure 3-22 illustrates the
electrical symbols commonly found in schematic
diagrams.
Loose connections are located by checking all
connectors in the circuit. A connector that can
be turned by hand is loose and should be tightened
handtight.
A continuity check is simply a matter of
determining whether or not the circuit to the valve,
or other electrically controlled unit, is complete.
The check for continuity may be made with a test
lamp, which can be drawn from supply.
To perform a continuity check, the connector
at the electrically controlled unit is first dis-
connected. Then, with all necessary switches and
circuit breakers closed, the test lamp is connected
into the circuit at the electrical connector. The
lamp thus indicates whether or not the circuit is
complete.
Continuity checks may also be made with the
use of a multimeter. A multimeter is an
instrument used for measuring resistance, voltage,
or amperage.
Troubleshooting
Troubleshooting is the process of locating a
malfunctioning component or other unit in a
Figure 3-22.—Electrical symbols.
3-35
