Dodge ZB 2005 Service Manual page 1393

GENERAL INFORMATION
low side control of the BCM. This circuit is electron-
ically controlled and continuously monitored for
malfunctions.
Accessory relay
The accessory relay works in conjunction with the
BCM's power accessory delay feature to control the
operation of the radio and power outlet. The acces-
sory relay is turned on through high side control on
the BCM. This circuit is electronically controlled
and continuously monitored for malfunctions. De-
pending on the ignition switch position, the acces-
sory relay will remain on or will time-out and turn
off. The accessory relay remains on in the RUN and
ACCY positions of the ignition switch. In the UN-
LOCK and OFF positions, the relay will remain
energized for 120 seconds then turn off. During this
time-out period, if the driver door is opened and the
ignition key is removed, the relay will turn off
immediately. While the ignition switch is in RUN
and the clutch and START button is pressed (and
not ignored), the relay will also drop-out, then
resume operation. Accessory relay operation is most
noticeable by observing the operation of the radio.
Both Driver and passenger windows will work dur-
ing accessory delay. NOTE: The windows cannot
be driven up during accessory delay if the
door is ajar. NOTE: A faulted ignition switch
will cancel delay.
Passenger Window Relays
There are two relays controlling the Up & Down
function of the Power windows. The BCM controls
the window Up relay coil with a High side driver.
This driver has Short Current diagnostics. The
BCM controls the Down relay coil with a Low side
driver. This driver has Open, Short to ground or
Short to Voltage diagnostics.
Horn relay
The horn relay operates through a direct wire
input to the BCM from the horn switch. The relay
responds to the horn switch, remote door lock and
VTSS alarm functions. The horn relay coil is con-
trolled by the BCM. Under normal operating condi-
tions, if the horn is pressed for longer than 30
seconds, the BCM will automatically deactivate the
horn to prevent damage to it. The BCM will re-
activate control of the relay after a 25 second
cool-down period. This circuit is electronically con-
trolled and continuously monitored for malfunc-
tions.
Front blower relay
The BCM powers the blower relay in ignition
RUN. The PDC powers the blower motor through
the closed relay contacts. To govern Low, M1 & M2
blower speeds, current flows from the blower motor
through the blower resistor. For High speed, cur-
rent flows from the blower motor to the A/C-Heater
Control to allow for blower operation should the
resistor fail. The ground path is supplied through
the A/C-Heater Control.
Rear Window Defogger (EBL) relay
The rear defrost switch is part of the A/C-Heater
Control Module (Manual Temp). When the ignition
switch is in the RUN position and the rear defrost
switch is turned on, the A/C-Heater Control Module
controls the relay. The BCM Controls the fused
ignition switch output circuit to the EBL relay coil.
The relay provides voltage to the rear window
defrost grid, and ground is attached to the vehicle
body. The relay will only allow the rear defrost to
operate in the RUN position. This circuit is elec-
tronically controlled and continuously monitored
for malfunctions.
3.9 HEATING & A/C SYSTEM
3.9.1 SYSTEM AVAILABILITY
•
A Single-Zone HVAC system is available in these
vehicles.
3.9.2 SYSTEM CONTROLS
The A/C-Heater Control Module:
•
is fully addressable with the DRBIII .
•
communicates over the Programmable Commu-
nication Interface Multiplex System (PCI) Bus.
• provides an A/C request to the Powertrain Con-
trol Module (PCM) over the PCI Bus when com-
pressor operation is desired.
• controls EBL operation.
• controls blower motor operation, providing four
blower speeds (Low, M1, M2, & High).
•
controls electric door actuator operation.
The Single-Zone HVAC system uses:
• one, two-wire electric blend door actuator.
• two, two-wire electric mode door actuators.
•
one, two-wire electric recirculation door actuator.
A simplified control system for operation of the
mode, recirculation, and temperature control ac-
tuators provides positive positioning without the
complexity of feedback from position sensors.
The A/C Heater Control Module knows the num-
ber of operating actuator revolutions required for
full door travel as well as the number of actuator
commutator pulses per revolution. Using these
parameters, the A/C Heater Control Module runs
the actuator for the number of commutator
pulses that correspond to the desired door posi-
tion. To maintain accuracy, the system recali-
brates itself periodically at known zero and full
travel conditions.
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