Dodge RAM TRUCK 1500 1995 Service Manual page 657

BR
8W-42 AIR CONDITIONING/HEATER
8W
- 42 - 1
AIR CONDITIONING/HEATER
GENERAL INFORMATION
This section of the wiring diagrams covers the op­
eration of the Heater only and the Heater-A/C sys­
tems.
Several fuses supply power for the A/C-Heater sys­
tem. Fuse B, a 20 amp, from the Power Distribution
Center (PDC) supplies battery voltage on circuit F31
to the contact side of the A/C compressor clutch relay.
Circuit'F31 is HOT at all times.
In the START or RUN position, the ignition switch
connects circuit Al from fuse 3 in the PDC to circuit
A21. Circuit A21 feeds fuse 9, a 10 amp, in the fuse
block. Circuit F18 connects from fuse 9 to the coil
side of the A/C compressor clutch relay
In the RUN position only, the ignition switch con­
nects circuit A2 from fuse 2, a 40 amp, in the PDC to
circuit A22. Circuit A22 supplies voltage to a bus bar
in the fuse block. Fuse 2, a 30 amp, connects to bus
bar and protects circuit CI which feeds the blower
motor.
Circuit E2 from fuse 13 in the fuse block powers
the illumination lamps in the A/C heater control
switch.
BLOWER MOTOR
When the ignition switch is in the RUN position,
circuit A2 from fuse 2, a 40 amp, in the Power Dis­
tribution Center (PDC) connects with circuit A22.
Circuit A22 supplies voltage to a bus bar in the fuse
block that powers fuse 2. Fuse 2 protects circuit CI
which supplies battery voltage to the blower motor.
From the blower motor, circuit C7 splices to the
blower motor resistor and the A/C-Heater control
switch.
The ground path for the blower motor is through
the circuits that connect from the blower motor resis­
tor block and then through the fan switch in the A/C
heater controls to circuit Z3. The blower motor resis­
tor block consists of three resistors connected in se­
ries (only two on the heater only vehicles).
Each resistor in blower motor resistor block is
spliced to the fan switch on separate circuits; C4, C5,
C6, and C7. Depending on fan switch position, volt­
age passes through one or more resistors to ground.
Blower motor fan speed is controlled by the number
of resistors voltage passes through to ground.
When the fan switch is in the LOW position, circuit
C4 provides the ground path. In the Ml position, cir­
cuit C5 provides ground. In the M2 position, the
ground path is through circuit C6. Circuit C7 pro­
vides path for ground when the switch is in the
HIGH position.
AIR CONDITIONING OPERATION
When the A/C-Heater control switch is moved to an
A/C position or the defrost position, and the A/C low
pressure and high pressure switches are CLOSED,
the Powertrain Control Module (PCM) receives an
A/C request signal on circuit C20. Circuit C20 con­
nects to cavity 27 of the PCM.
After receiving the A/C request signal, the PCM
supplies ground for the coil side of the A/C clutch re­
lay on circuit C13. Circuit C13 connects to cavity 34
of the PCM. Circuit F18 supplies battery voltage to
the coil side of the relay. Circuit F31 from fuse B in
the Power Distribution Center (PDC) supplies volt­
age to the contact side of the relay.
When the PCM grounds the A/C compressor clutch
relay, the contacts close and connect circuits F31 and
C3. Circuit C3 supplies voltage to the A/C compressor
clutch. Ground for the compressor clutch is provided
on circuit Zll.
The A/C compressor clutch connector has a built-in
diode. The diode controls the induced voltage that re­
sults from the magnetic field collapsing when the
clutch disengages. The diode provides a current path
to protect other components and systems.
HELPFUL INFORMATION
• Check the 40 amp fuses located in cavity 2, and 3
of the PDC
• Check the 30 amp fuse located in cavity 2 of the
fuse block
• Check the 10 amp fuse located in cavity 9 of the
fuse block