Automotive Electrical and Electronic Systems Classroom Manual Fifth Edition Update by John F. Kershaw

Body Accessory Systems Operation 323
Figure 15-13. Non-BCM-controlled ECC systems ground the compressor clutch through the lowpressure
switch and provide power through the power module (A). BCM-controlled ECC systems send
power through a fuse and a power steering cutout switch, and cycle the ground through the power module
(B). (GM Service and Parts Operations)
CLASS 2 IPM-
CONTROLLED HVAC
SYSTEMS
GM Electronically Controlled
Blower Motor
HVAC Module
Most of the luxury model cars, including GM,
have automatic heating, ventilating, and air
conditioning (HVAC) systems that are computer
controlled (Figure 15-14). The HVAC control
module is a computer device that interfaces
between the operator and the HVAC system
to maintain air temperature and distribution settings.
The control module sends switch input
data to the instrument panel module (IPM) and
receives display data from the IPM through signal
and clock circuits. The control module does not
retain any HVAC DTCs (diagnostic trouble codes)
or settings.
Instrument Panel Module (IPM)
A function of the IPM operation is to process
HVAC system inputs and outputs. Also, the IPM
acts as the HVAC control module’s Class 2 interface.
The battery positive voltage circuit provides
power that the IPM uses for Keep-Alive
Memory (KAM). If the battery positive voltage
circuit loses power, then all HVAC DTCs and
settings will be erased from KAM. The ignition
voltage circuit provides a device on signal. The
IPM supports the following features:
• Driver set temperature
• Passenger set temperature