Jeep 200 Cherokee Service Manual page 545

8N - 8 ELECTRICALLY HEATED SYSTEMS
GENERAL INFORMATION
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . 8
DESCRIPTION AND OPERATION
HEATED SEAT SWITCH. . . . . . . . . . . . . . . . . . . . . 8
SEAT HEAT INTERFACE MODULE. . . . . . . . . . . . . 9
HEATED SEAT RELAY . . . . . . . . . . . . . . . . . . . . . . 9
HEATED SEAT ELEMENT and SENSOR . . . . . . . . 9
DIAGNOSIS AND TESTING
HEATED SEAT SYSTEM . . . . . . . . . . . . . . . . . . . . 9
GENERAL INFORMATION
INTRODUCTION
Individually controlled electrically heated front
seats are available factory-installed optional equip-
ment on this model. The seat heaters will only oper-
ate when the ignition switch is in the ON position,
and the surface temperature at the front seat heating
element sensors is below the designed temperature
set points of the system. The heated seat system will
not operate in ambient temperatures greater than
about 32° C (90° F).
There are separate momentary, tactile, two-direc-
tional rocker switches located in the center console
with center NEUTRAL, HI and LO positions for each
front seat. Depressing the rocker switch to its
momentary HI or LO position signals the Seat Heat
Interface Module (SHIM) to power the selected
heated seat and maintain the requested temperature
setting (HI or LO). Each switch has a HI and LO
Light-Emitting Diode (LED) which, via the SHIM,
illuminates to give a visual indication that the sys-
tem is in the HI or LO mode. The LO heat set point
is about 32° C (90° F), and the HI heat set point is
about 38° C (100° F). The system shall be deactivated
whenever the same set position is depressed a second
time and shall change states directly when switching
from HI to LO or vice versa. The system shall be
deactivated whenever the ignition switch is placed in
the off position. When the ignition switch is placed
back in the run position, the heated seat system
shall remain deactivated until a momentary switch is
depressed. When a seat heater is turned on, a sensor
located near the seat cushion electric heater element
provides the SHIM with input indicating the surface
temperature of the seat cushion. If the surface tem-
perature input is below the temperature set point of
the SHIM for the selected temperature setting, an
HEATED SEAT SYSTEM
TABLE OF CONTENTS
page
HEATED SEAT SWITCH . . . . . . . . . . . . . . . . . . . . 10
HEATED SEAT ELEMENT and SENSOR. . . . . . . . 11
HEATED SEAT RELAY . . . . . . . . . . . . . . . . . . . . . 11
SEAT HEAT INTERFACE MODULE. . . . . . . . . . . . 12
REMOVAL AND INSTALLATION
HEATED SEAT SWITCH . . . . . . . . . . . . . . . . . . . . 12
SEAT HEAT INTERFACE MODULE. . . . . . . . . . . . 12
HEATED SEAT RELAY . . . . . . . . . . . . . . . . . . . . . 12
N-FET Transistor within the SHIM energizes the
heating elements in the seat cushion and back. When
the sensor input indicates the correct temperature
set point has been achieved, the SHIM de-energizes
the N-FET. The SHIM will continue to cycle the
N-FET as needed to maintain the temperature set
point.
The SHIM will automatically turn off the heating
elements if it detects a short or an open in the heat-
ing element or a sensor out of range. These condi-
tions will also cause the SHIM to notify the occupant
of the failure via flashing the heated seat switch
LED's as discussed later.
Switched battery power to the SHIM is supplied by
the heated seat relay mounted to the seat cushion
frame with the SHIM under the right front seat. The
battery feed is protected by a circuit breaker located
in the junction block.
Following are general descriptions of the major
components in the heated seat system. Refer to
8W-63 - Power Seat With Heated Seats in Group 8W
- Wiring Diagrams for complete circuit descriptions
and diagrams.
DESCRIPTION AND OPERATION
HEATED SEAT SWITCH
The heated seat switch assembly is located on the
center console where the ashtray is normally located
(Fig. 1). The two momentary, two-directional rocker
switches, one switch for each front seat, provide a
resistor-multiplexed signal to the Seat Heat Interface
Module (SHIM). Each switch has center NEUTRAL,
and momentary LO and HI positions so that both the
driver and the front seat passenger can select a pre-
ferred seat heating mode.
Each switch has two telltales (LED's) which indi-
cate the mode of the heater of the respective seat.
XJ
page