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3.11 HEATING & A/C SYSTEM
3.11.1 AUTOMATIC TEMPERATURE
CONTROL (ATC)
CAUTION: Automatic Temperature Control
(ATC) Modules in early build CS vehicles use
version 17 software. ATC Modules in late
build CS vehicles use version 19 software.
Do NOT exchange ATC modules between
vehicles. Use the DRBIII
version software the ATC Module is using by
selecting Body Systems, then Automatic
Temperature Control, and then selecting
Module Display. Failure to follow these
instructions can result in improper HVAC
system operation.
3.11.1.1 SYSTEM AVAILABILITY
•
The Automatic Temperature Control (ATC)
system is a Dual-Zone Air Conditioning Sys-
tem with a Rear Booster Blower.
3.11.1.2 SYSTEM CONTROLS
The ATC Module:
•
is fully addressable with the DRBIII .
•
communicates over the Programmable Commu-
nication Interface Multiplex System (PCI) Bus.
•
provides an A/C request over the PCI Bus to the
Powertrain Control Module (PCM) when com-
pressor operation is desired.
•
uses input from the evaporator temperature sen-
sor to prevent evaporator freeze up while main-
taining optimum cooling performance.
•
has dual-zone temperature-controls to provide a
wide side-to-side variation in temperature to
meet the needs of driver and the front seat
passenger.
•
has dual infrared (I/R) sensors mounted in the
ATC Module's face which independently mea-
sure surface temperature to maintain occupant
comfort levels.
•
can be operated in a manual mode.
•
provides an EBL relay on request over the PCI
Bus to the Integrated Power Module (IPM) when
EBL operation is desired.
•
provides a Blower Relay on request over the PCI
Bus to the Integrated Power Module (IPM).
•
controls front blower operating speed, providing
6 blower speeds in manual mode and infinite
blower speeds in automatic mode.
•
to verify which
•
•
19
GENERAL INFORMATION
provides a blower delay function for cold engine
blower lock out.
A Blower Speed Clamping feature minimizes
occupant
discomfort
amount of warm air coming out of the HVAC
system should the Powertrain Control Mod-
ule (PCM) disable A/C compressor operation
while the Automatic Temperature Control
(ATC) is set in an automatic mode. The PCM
disables the A/C compressor if the A/C is too
low, if the A/C pressure is too high, if engine
overheating is immanent, or if an engine
overheating condition exists. For ATCs with
version 17 software the ATC clamps the
blower speed if the PCM has disabled the A/C
compressor. For ATCs with version 19 soft-
ware the ATC clamps the blower speed if the
outside air temperature is greater than 50°F
(10°C) and the PCM has disabled the A/C
compressor. For all ATCs this means that the
ATC will not adjust blower speed automati-
cally when the clamping feature is enabled,
e.g. if the clamping feature is enabled while
in Auto Lo the blower will continue to run in
low speed; if the clamping feature is enabled
while in Auto Lo and the operator selects
Auto Hi the blower will continue to run in low
speed; if the clamping feature is enabled
while in Auto Hi the blower will continue to
run at the highest speed. In any case the
opeator can manually change the blower
speed as desired. When diagnosing blower
related symptoms verify that none of the
above conditions for disabling the A/C com-
pressor exist before diagnosing the blower
circuits and components.
controls rear booster fan operating speed in
automatic mode, providing infinite fan speeds.
activates and deactivates the Rear Booster Fan
Rear Control Switch.
The separate Front Blower Power Module
and Rear Booster Fan Power Module operate
as follows: When blower operation is desired,
the power module provides a 12.0 volt signal
to the ATC Module over a control circuit. The
ATC Module provides a variable duty cycle
ground to the 12.0-volt signal based on input
from the blower switch. When the blower
speed is set to low, the ATC Module provides
a short duty cycle (less time grounding the
signal voltage). As higher blower speeds are
requested, the ATC Module increases the
duty cycle (more time grounding the signal
voltage). When the highest blower speed is
requested, the duty cycle increases to where
the signal pattern is almost a flat line (with
brief voltage spikes).
by
controlling
the
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