Central Tire Inflation System - Hummer H1 Service Manual

6-30 Wheels and Tires/Central Tire Inflation System (CTIS)

CENTRAL TIRE INFLATION SYSTEM

The optional Central Tire Inflation System (CTIS) is unique to
the HUMMER. The CTIS allows the driver to increase or de-
crease tire pressure based on terrain and climate conditions.
The system can also be used to direct air to a tire that has a
leak.
The CTIS controls are located on the instrument panel. An in-
flate/deflate switch determines if air is added to the tires or re-
leased from the tires. When the tires are being inflated, an
indicator light on the instrument panel illuminates. If the pres-
sure in any of the tires drops to 8 psi (55 kPa) or below, the low
pressure indicator light will illuminate and an alarm will
sound. If the tire pressure ever exceeds 55 psi (379 kPa), a re-
lief valve automatically relieves any excess pressure. The tire
selector valve position determines whether the pressure in the
front, rear or all four tires will be adjusted. The air pressure
gauge indicates the current pressure in the tires. Refer to the
short, white needle for front tire pressure and the longer, or-
ange needle for the pressure in the rear tires. Temperature rise
and fall affects air pressure in a tire. As the vehicle is operated
it is typical for the air pressure to rise 3-5 psi (21-34 kPa). As
the wheels and tires cool down, the air pressure will drop. This
is normal and such a drop in tire pressure does not indicate any
leaks in the system.
The CTIS consists of an electric air compressor that pumps air
through a series of valves, tubes, and hoses to the front and/or
rear tires. Compressed air travels through the manifold where
three electric valves connected in parallel direct the com-
pressed air to the front, rear or both tires. When deflation is se-
lected, air is routed from the tires through the three electric
valves and is exhausted through the deflate valves
(Figure 6-49).
Each wheel assembly has a manual quick-disconnect valve
which can be used to prevent air flow to and from the tire, such
as during long-term storage or while changing a tire. If the ve-
hicle will remain dormant for two weeks or more, it is a good
practice to disconnect the system at the wheels. These quick-
disconnect valves are also used to restrict air flow to the opera-
tional tires when the driver wants to direct air flow to a dam-
aged tire. For example, if a tire has a small puncture and has a
leak, the quick-disconnect valves on the operational tires can
be disconnected, enabling compressed air to be directed exclu-
sively to the leaking tire. This may maintain enough tire pres-
sure in the leaking tire to allow the driver to get the vehicle to
an appropriate location for safe tire repair or replacement
(Figure 6-50).
RADIAL TIRE
WHEEL
QUICK
DISCONNECT
FITTING
SPINDLE
PASSAGE
Figure 6-49: Central Tire Inflation System (CTIS)
TUBE SHIELD
Figure 6-50: Quick-Disconnect Valve
To disconnect the CTIS from the wheel assemblies, first turn
inflate/deflate switch to the OFF position. Release the four
quick-disconnect valve assemblies from all four spindles by
depressing the quick-disconnect valve tabs attached to the
valve spindle nuts (Figure 6-51). When the tabs are depressed,
the valve assemblies will spring away from the spindles about
1/2 inch (12.7 mm). To reconnect the quick-disconnect valve
assemblies, push the valve assemblies toward the spindles until
they click into place.
_______________
1-PIECE
RUNFLAT
BEADLOCK
HALFSHAFT
AIR SEAL
FROM
COMPRESSOR
SPINDLE
®