Rear Glass Heating Grid Description And Operation; Outside Mirror Heating Grid Description And Operation; Defogger Switch Description And Operation; Instrument Cluster Description And Operation - Jeep Cherokee 2000 Service Manual

8N - 2 ELECTRICALLY HEATED SYSTEMS
GENERAL INFORMATION (Continued)
the defogger switch is turned on again during the
same ignition cycle, the defogger system will auto-
matically turn off after about five minutes.
The defogger system will automatically shut off if
the ignition switch is turned to the Off position, or it
can be turned off manually by depressing the instru-
ment panel switch. Following are general descrip-
tions of the major components in the defogger
system. Refer to the owner's manual in the vehicle
glove box for more information on the features, use
and operation of the defogger system.
DESCRIPTION AND OPERATION
REAR GLASS HEATING GRID
The heated rear window glass has two electrically
conductive vertical bus bars and a series of horizon-
tal grid lines made of a silver-ceramic material,
which is baked on and bonded to the inside surface of
the glass. The grid lines and bus bars comprise a
parallel electrical circuit.
When the rear window defogger switch is placed in
the On position, electrical current is directed to the
rear window grid lines through the bus bars. The
grid lines heat the rear window to clear the surface
of fog or snow. Protection for the heated grid circuit
is provided by a fuse in the Power Distribution Cen-
ter (PDC).
The grid lines and bus bars are highly resistant to
abrasion. However, it is possible for an open circuit
to occur in an individual grid line, resulting in no
current flow through the line.
The grid lines can be damaged or scraped off with
sharp instruments. Care should be taken when clean-
ing the glass or removing foreign materials, decals,
or stickers from the glass. Normal glass cleaning sol-
vents or hot water used with rags or toweling is rec-
ommended.
A repair kit is available to repair the grid lines and
bus bars, or to reinstall the heated glass pigtail
wires.
OUTSIDE MIRROR HEATING GRID
Vehicles equipped with the optional heated mirror
package have an electric heating grid located behind
the mirror glass of each outside rear view mirror.
The heated mirrors are controlled by the rear win-
dow defogger switch. Electrical current is directed to
the heating grid inside the mirror only when the rear
window defogger switch is in the On position.
If the outside mirror heating grids and the rear
window heating grid are all inoperative, diagnosis of
the rear window defogger system should be per-
formed as described in this group. If the outside mir-
ror heating grids are inoperative, but the rear
window heating grid is operating as designed, refer
to Power Mirror in the Diagnosis and Testing section
of Group 8T - Power Mirror Systems for diagnosis of
the mirror heating grids.
The heating grid behind each outside mirror glass
cannot be repaired and, if faulty or damaged, the
entire power mirror unit must be replaced. Refer to
Power Mirror in the Removal and Installation section
of Group 8T - Power Mirror Systems for the service
procedures.
DEFOGGER SWITCH
The rear window defogger switch is installed in the
instrument panel accessory switch bezel, which is
located near the bottom of the instrument panel cen-
ter bezel area, below the heater and air conditioner
controls. The momentary-type switch provides a
hard-wired ground signal to the instrument cluster
each time it is depressed. The instrument cluster
rear window defogger timer and logic circuitry
responds by energizing or de-energizing the rear win-
dow defogger relay.
Energizing the rear window defogger relay pro-
vides electrical current to the rear window defogger
grid and, if the vehicle is so equipped, the outside
rear view mirror heating grids. An amber indicator
lamp in the defogger switch, which lights to indicate
when the defogger system is turned On, is also pow-
ered by the defogger relay output.
The defogger switch illumination lamp and indica-
tor lamp bulbs are serviceable. The defogger switch
cannot be repaired and, if faulty or damaged, it must
be replaced.
INSTRUMENT CLUSTER
The instrument cluster is an electromechanical
unit that contains integrated circuitry and internal
programming to perform a variety of functions. The
instrument cluster circuitry monitors hard-wired
switch inputs, as well as message inputs received
from other vehicle electronic control modules on the
Chrysler Collision Detection (CCD) data bus network.
The instrument cluster uses these many inputs
along with its internal programming and integral
timer and logic circuitry to perform the functions of
the rear window defogger timer on this model. The
instrument cluster circuitry also has a self-diagnostic
capability. Refer to Instrument Cluster in Group 8E -
Instrument Panel Systems for more information on
this feature.
However, there are no diagnostics available for the
rear window defogger timer and logic circuitry.
Therefore, the diagnosis for this system consists of
confirming the presence of a rear window defogger
switch input signal at the instrument cluster connec-
tor, and the resulting rear window defogger relay
XJ