Jeep 1996 Grand Cherokee Service Manual - page 1396
AMBIENT TEMPERATURE SENSOR
Models with the optional automatic temperature
control system use an input from the ambient tem-
perature sensor. The sensor is located in front of the
condenser and behind the grille on the center radia-
tor support.
The ambient temperature sensor is hard-wired to
the Body Control Module (BCM). The BCM places an
ambient temperature message on the CCD data bus
for use by the overhead console for the thermometer
function, and for use by the ATC controller.
The ambient temperature sensor is a Negative
Temperature Coefficient (NTC) thermistor or temper-
ature sensitive resistor. The ATC controller uses this
sensor input to monitor the outside air temperature.
However, because heat from the radiator and con-
denser can affect the accuracy of this sensor input
when the vehicle is not moving, this input is only
used by the ATC system when the vehicle is in
motion.
The
ambient
temperature
sensor
cannot
be
adjusted or repaired and, if faulty or damaged, it
must be replaced.
BLOWER MOTOR
The blower motor and blower wheel are located in
the right end of the heater-A/C housing, below the
glove box. It can be removed from the passenger com-
partment side of the housing. The blower motor cir-
cuit is protected by a fuse in the junction block.
The blower motor will only operate when the igni-
tion switch is in the On position, and the heater-A/C
mode control switch is in any position, except Off. On
models with the standard manual temperature con-
trol system, the blower motor speed is controlled by
the blower motor switch and resistor. On models with
the optional ATC system, the blower motor speed is
controlled by the blower motor switch and the power
module.
The blower motor cannot be repaired and, if faulty,
must be replaced.
BLOWER MOTOR POWER MODULE
Models equipped with the optional ATC system
have a blower motor power module. The power mod-
ule allows infinitely variable blower motor speeds.
The power module is mounted on the heater-A/C
blower housing in the same location used for the
blower motor resistor on manual temperature control
systems.
The power module output to the blower motor can
be controlled manually by using the blower motor
switch knob on the heater-A/C control panel, or auto-
matically by the circuitry of the ATC controller. In
either case, the ATC controller sends the correct
pulse width modulated signal to the power module to
provide the proper blower motor speed.
The power module cannot be repaired and, if
faulty, it must be replaced.
BLOWER MOTOR RESISTOR
Models with the standard manual temperature
control system have a blower motor resistor. The
blower motor resistor contains several resistor wires.
The blower motor receives ignition switched battery
feed from a fuse in the junction block. The blower
motor speed is controlled by changing the resistance
in the blower motor ground path through the blower
motor switch and the blower motor resistor wires.
With the blower motor switch in the lowest speed
position, the ground path for the motor is applied
through all of the resistor wires. Each higher speed
selected with the blower motor switch applies the
blower motor ground path through fewer of the resis-
tor wires, increasing the blower motor speed. When
the blower motor switch is in the highest speed posi-
tion, the blower motor resistor is bypassed and the
ground circuit is applied directly to the blower motor.
The blower motor resistor cannot be repaired and,
if faulty, must be replaced.
Fig. 3 Accumulator
ZJ
HEATING AND AIR CONDITIONING
24 - 5
DESCRIPTION AND OPERATION (Continued)