Circuit/System Description

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2012 GMC Yukon XL, 2012 GMC Yukon, 2012 Chevrolet Tahoe, 2012 Chevrolet Suburban, and 2012 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

Each seat has two ventilation heating and cooling modules, one located under the seat cushion to control cushion temperature and one located in the seat back to control seat back temperature.

Each ventilation heating and cooling module contains the necessary electronics to control the heating and cooling functions, as well as a thermo-electric device (TED) and blower motor used for the cooling functions. The heating function is provided by a separate heating element which is also controlled by the ventilation heating and cooling module.

In the description below, the TEDs and blower motors are referenced independently even though they are packaged together as indicated above.

The heated and cooled seat switches are located on the door panels. When a heated or cooled seat switch is pressed, a low reference signal is applied through the switch signal circuit to the door lock/window switch. In response to this signal, the door lock/window switch simultaneously illuminates the appropriate heated/cooled switch indicators and sends a serial data message to the memory seat module (MSM) indicating the heat or cool seat request. The MSM then sends a low side pulse width modulation (PWM) signal through the heated/cooled seat mode signal circuit to both ventilation and cooling modules for a given seat.

Battery positive voltage is supplied to the ventilation heating and cooling modules through a fuse located in the I/P fuse block.

When a cooled seat request is received, the seat ventilation heating and cooling modules apply voltage to the TEDs and a pre-determined voltage to the blower motors. When a heated seat request is received, the seat ventilation heating and cooling modules apply battery voltage and ground through the control circuits to the seat heating elements. In order to determine seat temperature, each ventilation module supplies a 5 V signal and a low reference to the temperature sensors that are attached to the seat cushion and seat back heater elements. The temperature sensors are variable resistors, their resistance changes as the temperature of the seat changes. Then based on the seat temperature, the ventilation module controls the voltage level that it applies to the TED and blower motor when in the cool mode, or it cycles the power supply to the heater element ON and OFF when in the heat mode.