freightliner Cargo - Primary and Secondary Air Pressure Gauges; Fuel Gauge; Intake-Air Restriction Indicator

The voltmeter will normally show approximately 13.7 to
14.1 volts when the engine is running. The voltage of a
fully charged battery is 12.7 to 12.8 volts when the en-
gine is stopped. A completely discharged battery will
produce only about 12.0 volts. The voltmeter will indi-
cate lower voltage as the vehicle is being started or
when electrical devices in the vehicle are being used.
If the voltmeter shows an undercharged or overcharged
condition for an extended period, have the charging
system and batteries checked at a repair facility.
On a vehicle equipped with a battery isolator system,
the voltmeter measures the average voltage of all the
batteries when the engine is running. When the engine
is stopped, the voltmeter shows only the gel cell battery
voltage and does not indicate the voltage of the engine-
starting batteries.
CAUTION
Gel cell batteries can be damaged if the battery
voltage is allowed to drop below 12.0 volts or if the
charging voltage is more than 14.1 volts. Start the
engine to recharge the gel cell before the battery
becomes fully discharged. If an external charger is
needed, disconnect the gel cell battery and use only
an external battery charger that has been approved
for gel cell batteries.
Primary and Secondary Air Pressure
Gauges
These air pressure gauges (see Fig. 3.20) register the
constant pressure in the primary and secondary air sys-
tems. Normal pressure, with the engine running, is 95
to 125 psi (655 to 862 kPa) in both systems. A low-air-
pressure warning light and buzzer, connected to both
the primary and secondary systems, activate when air
pressure in either system drops below a minimum pres-
sure of 62 to 68 psi (427 to 469 kPa). When the engine
is started, the warning light and buzzer remain on until
air pressure in both systems exceeds minimum pres-
sure. An air pressure gauge that registers pressure in
both the primary and secondary systems may be in-
stalled on some vehicles.
Fuel Gauge
The fuel gauge (see Fig. 3.21) indicates the amount of
fuel in the fuel tank(s).
Intake-Air Restriction Indicator
An intake-air restriction indicator measures the vacuum
on the engine side of the air cleaner at the air cleaner
outlet. If the yellow signal stays locked at or above the
values shown in Table 3.3, after the engine is shut
down, service the air cleaner, then reset the indicator by
pressing the reset button.
Driver Controls and Instruments
3.15