Jeep 1997 Grand Cherokee Service Manual page 1304

8W - 42 - 16
DESCRIPTION AND OPERATION (Continued)
pressure switch connects circuit C21 to ground cir-
cuit Z1. If the A/C low pressure and high pressure
switches are closed, the PCM senses the A/C request
signal on circuit C3.
After sensing the A/C request signal, the PCM sup-
plies ground for the coil side of A/C compressor clutch
relay on circuit C13. Circuit F99 from fuse 18 in the
PDC powers the coil side of the relay.
When the PCM grounds the A/C compressor clutch
relay, the contacts close and connects circuit F250
from fuse 21 in the PDC to circuit C2. Circuit C2
supplies power to the case grounded A/C compressor
clutch.
The A/C compressor clutch has a built-in diode.
The diode controls the induced voltage that results
from the magnetic field collapsing when the clutch
disengages. The diode provides a current path to pro-
tect other components and systems.
HELPFUL INFORMATION
Circuit A900 from fuse 3 in the PDC powers circuit
F250 through PDC fuse 21.
RECIRCULATION DOOR MOTOR—AUTOMATIC
TEMPERATURE CONTROL
When the ignition switch is in the RUN position, it
connects circuit A1 from fuse 8 in the Power Distri-
bution Center (PDC) to circuit A22. Circuit A22 pow-
ers circuit F71 through fuse 12 in the junction block.
Circuit F71 feeds the recirculation door motor. Cir-
cuit F71 also connects to the Automatic Temperature
Control (ATC) module.
Circuits C32 and C33 from the ATC module con-
nect to the recirculation door motor. Circuits C32 and
C33 provide ground for the motor.
MODE DOOR MOTOR—AUTOMATIC
TEMPERATURE CONTROL
Circuit C40 from the Automatic Temperature Con-
trol (ATC) module supplies 5 volts to the position
switch in the mode door motor. The ATC module
receives the sensor signal from the mode door motor
on circuit C39. Circuit D41 provides ground for the
mode door position sensor. Circuit D41 connects to
the ATC module.
The ATC module operates the mode door motor on
circuits C37 and C38.
BLEND DOOR MOTOR—AUTOMATIC
TEMPERATURE CONTROL
Circuit C40 from the Automatic Temperature Con-
trol (ATC) module supplies 5 volts to the position
8W - 42 AIR CONDITIONING/HEATER
switch in the blend door motor. The ATC module
receives the sensor signal from the blend door motor
on circuit C36. Circuit D41 provides ground for the
mode door position sensor. Circuit D41 connects to
the ATC module.
The ATC module operates the mode door motor on
circuits C35 and C34.
BLOWER MOTOR—AUTOMATIC TEMPERATURE
CONTROL
When the operator selects blower motor HIGH
speed operation, the Automatic Temperature Control
(ATC) module grounds high speed blower motor relay.
For any speed other than HIGH, the blower power
module supplies battery voltage for the blower motor.
BLOWER MOTOR POWER MODULE
When the operator selects any blower motor speed
other than HIGH, the blower motor power module
supplies voltage for the blower motor. Circuit A19
from fuse 7 in the Power Distribution Center (PDC)
supplies battery voltage to the blower motor power
module.
The voltage level fed to the blower motor depends
on the blower speed selected by the operator. Slower
speed selections provide lower voltage to the motor.
The blower motor power module feeds the blower
motor on circuit C42. Circuit Z4 provides ground for
the blower motor and the blower motor power mod-
ule.
Circuit C43 from the power module connects to the
ATC module. The ATC module controls feedback on
circuit C43.
HIGH SPEED BLOWER MOTOR RELAY
Circuit A19 from fuse 7 in the Power Distribution
Center supplies battery voltage to the coil and con-
tacts sides of the high speed blower motor relay. The
ATC module provides ground for the coil side of the
relay on circuit C41.
When the ATC module grounds the high speed
blower motor relay, the relay contacts close and con-
nect circuit A19 to circuit C42. Circuit C42 connects
to the blower motor and the ATC module. Circuit Z4
provides ground for the blower motor.
ZG