If the voltmeter shows an undercharged or over-
charged condition for an extended period, have the
charging system and batteries checked at an autho-
rized Freightliner service 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 en-
gine is off, the voltmeter shows only the isolated bat-
tery voltage and does not indicate the voltage of the
engine-starting batteries.
Optional Instruments
Optional instruments, typically located on the auxil-
iary dash panel or right-hand control panel, are not
found on every vehicle. They are listed here in alpha-
betical order, to make the information easier to find.
Air Restriction Gauge
The air intake restriction gauge measures the
vacuum on the engine side of the air cleaner. On
standard installations, it is mounted on the air intake
duct in the engine compartment.
As an option for easier viewing, the air intake restric-
tion indicator (see
Fig. 3.16
) can be mounted on the
dash, usually on the right-hand control panel.
NOTE: Rain or snow can wet the filter and
cause a higher than normal reading temporarily.
Air intake restriction vacuum is measured in inches
of water (inH
2
O). For vehicles equipped with a
graduated indicator or a restriction gauge on the
dash, check the gauge with the engine off. If the yel-
low signal stays locked in the red zone once the en-
gine is shut down, or is at or above the values
shown in
Table 3.4
, the air cleaner element needs to
be replaced.
Vehicles may be equipped with a go/no-go restriction
indicator without graduations (see
Fig. 3.17
) instead
of a graduated indicator.
Air Intake Maximum Restriction Values
Engine Make
*
Pre-EPA07
Engines (inH
2
O)
EPA07/EPA10
Engines (inH
2
O)
Caterpillar
25
—
Cummins
25
25
Detroit Diesel
20
22
Mercedes-Benz
22
22
*
Turbocharged engines must be checked at full load and governed en-
gine speed.
Table 3.4, Air Intake Maximum Restriction Values
10/10/2001
f610568
Fig. 3.16, Air Intake Restriction Indicator
04/08/2005
f090431
Fig. 3.17, Manual-Reset Air Restriction Indicator, Go/
No-Go
Instruments
3.12
