Tahoe 2WD V8-5.3L (2007)
Seat Fan: Description and Operation
HEATED/COOLED SEATS DESCRIPTION AND OPERATION
The driver and front passenger heated cooled seat system consist of the following components:
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HVAC Control Module
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Memory Seat Module
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Climate Control Seat Module
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Driver and passenger seat back heat/cool ventilation blowers
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Driver and passenger seat cushion heat/cool ventilation blowers
HVAC Control Module
The heated cooled seat system operation is controlled through the switch inputs of the HVAC control module. The heated cooled seat switches provide
3 inputs that are relayed to the Memory Seat Module (MSM) through GMLAN messages. Whenever one of the switches is pressed a message is sent
to the MSM indicating switch is active. During heated cooled seat operation the HVAC control module displays the switch symbol of the active
operating mode and the temperature level bars on the climate control display. The mode symbol and temperature bars that are displayed is determined
by a GMLAN message from the MSM.
Memory Seat Module
The memory seat module monitors the heated cooled seat switches through GMLAN message inputs and determines the heated cooled seat operating
modes and temperature levels. When heated or cooled seat switch active signals are received through GMLAN messages, and vehicle conditions are
appropriate to allow heated or cooled seat operation, the memory seat module (MSM) will calculate the switch activations and determine the heated or
cooled seat operating modes. When the MSM activates a heated cooled seat function an indicator control GMLAN message is sent to the HVAC
control module. The MSM controls the operating mode of the Climate Control Seat Module (CCSM) through 2 pulse width modulation (PWM) signal
circuits. The left and right heated/cooled seat mode signal circuits are referenced from battery voltage by the CCSM and pulsed low by the MSM.
Each heated cooled seat is capable of operating in 3 modes with 3 temperature levels so the MSM uses 9 PWM frequencies for each signal circuit to
command the heated cooled seat modes to the CCSM.
Climate Control Seat Module
The Climate Control Seat Module (CCSM) is located under the passenger seat and controls 4 individual driver and passenger seat heat/cool ventilation
blowers. When the CCSM receives a heated cooled seat command through the left or right heated/cooled seat mode signal circuit, the appropriate seat
heat/cool ventilation blowers will be operated by the CCSM.
Seat Heat/Cool Ventilation Blowers
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. Heat or cool modes are determined by the polarity of the supply voltage to the TEDs. The climate control seat
modules (CCSM)s 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. 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.
