Circuit/System Description

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2007 GMC Yukon XL, 2007 GMC Yukon, 2007 Chevrolet Tahoe, 2007 Chevrolet Suburban, and 2007 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

The heated cooled seat system operation is controlled through the switch inputs of the HVAC control module. When a heated or cooled seat switch is pressed a GNLAN message is sent to the Memory Seat Module (MSM) indicating the switch is active. The MSM monitors the heated cooled seat switch inputs and determines the appropriate operating mode. When a heated or cooled seat function is activated the MSM will send a GMLAN message to the HVAC control module to illuminate the appropriate indicators and a PWM message to the Climate Control Seat Module (CCSM) to activate the appropriate heated cooled seat function. The CCSM controls heat/cool seat ventilation blowers located under the seat cushion and behind the seat back. The ventilation blowers are self contained electronic air conditioners consisting of a blower motor with an inlet air filter, thermal electric device (TED), temperature sensor, and waste air duct. The air flow from the blower is divided into 2 streams and directed across both sides of the TED, one side into vent passages through the seat foam and the other out the waste air duct. While the system is operating in either the heat or cool modes both heated and cooled air is generated as it passes across the TED. When voltage is applied to a TED, one side releases energy as heat, while the opposite side absorbs energy and gets cold. The supply voltage to the TEDs is controlled by the CCSM and the polarity determines which side gets hot or cool. When the polarity of the current flow to the TEDs is switched, the hot and cool sides of the TED reverse. The CCSM monitors the temperature of the air flow into the seat foam and continuously adjusts the blower speed and TED temperature by regulating the current flow through each component. The CCSMs rely on inputs from temperature sensors located in the ventilation blowers near the TEDs to control seat temperatures. The thermistors are 2 wire sensors supplied with a 5-volt referenced signal circuit and a low reference circuit from the CCSM. Resistance through the thermistors varies with temperature causing the heated seat sensor signal circuit voltage levels to decrease as the TED temperatures rise.