ker88839_ch15.qxd
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Body Accessory Systems Operation
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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 IPMCONTROLLED 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
