Heated/Cooled Seats

Heated/Cooled Seats Description and Operation

The driver and front passenger heated cooled seat system consist of the following components:

* Seat cushion ventilation heating and cooling module

* Seat back ventilation heating and cooling module

* Memory seat module

* Heated/cooled seat switches and HVAC control module (Escalade)

* Heated/cooled seat switch and door lock/window switch (Chevrolet and GMC)

Seat Ventilation Heating and Cooling Module Power and Ground

Battery positive voltage is supplied at all times to the seat ventilation heating and cooling modules through a 30 A fuse that is located in the I/P fuse block. This voltage is to supply power to the TEDs, the blower motors, and the seat heater elements. The heated and cooled seat system will operate only with the ignition in the ON position. Each seat ventilation heating and cooling module is grounded through the module ground circuit and G304 for both the driver and passenger seats.

Seat Ventilation Heating and Cooling Module

Each heated/cool seat has 2 ventilation heating and cooling modules, one located under the seat cushion and one located in the seat back. Each ventilation module contains a thermo-electric device (TED) and a blower motor. The TED is mounted downstream of the blower motor. Each TED consists of a circuit of positive and negative connections sandwiched between 2 ceramic plates. Each ceramic plate is equipped with copper fins for cool exchange. The air flowing past these fins is directed as conditioned air into the seat cushion and seat back or directed into the cabin as waste air.

A TED is essentially a solid state heat pump that is used to cool the air supply to the seat cushion and seat back. When voltage is applied to a TED, one side releases energy as heat, while the opposite side absorbs energy and gets cold.

During the following climate control seat system description and operation, the TEDs and blower motors will be referenced independently even though they are packaged together as a module.

Air Circulation

When the cool seat switch is pressed to initiate operation of the cooled seat system, cabin air is drawn through the ventilation heating and cooling module air filter, then directed through passages in the foam of the seat cushion and seat back to the seat's occupant. In order for the cooled seat system to operate to its optimum performance, it is crucial to have unrestricted air flow through the system. A dirty or restricted air filter, the blockage of an exhaust air duct, a misaligned heated/cool ventilation module, or incorrect foam installation of the seat cushion or seat back will all have negative effects on the cooled seat system operation.

Climate Control Seat System

Once a climate control seat system is activated, cabin air is drawn through the seat blower motors and directed across the fins of each of the TEDs located under the seat cushion and in the seat back. The air is cooled as it passes over the TEDs. This conditioned air is then directed through channels in the foam of the seat pad and through small holes in the seat cover to the occupant. Once the system is activated, the seat ventilation heating and cooling module uses a set of algorithms to control the temperature of the selected heating or cooling modes.

Memory Seat Module

The memory seat module (MSM) monitors the heated cooled seat switches through serial data message inputs and determines the heated cooled seat operating modes and temperature levels. The MSM controls the operating mode of the driver and passenger seats through separate pulse width modulation (PWM) signal circuits. The heated/cooled seat mode signal circuits are referenced from battery voltage by the ventilation heating and cooling modules 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 seat heating and cooling modules.

Modes of Operation

There are 3 modes available for the heated and cooled seat system operation, heated seat, cool seat, and back only heat operation. When a heat or cool seat mode signal request is received, both the seat cushion and seat back ventilation heating and cooling modules will be activated. When the seat BACK ONLY mode button is pressed, the seat cushion ventilation heating and cooling module is turned off leaving the seat back ventilation heating and cooling module ON.

Heated/Cooled Seat Switch and Door Lock/Window Switch

The heated and cooled seat system is controlled through the heated and cooled seat switches that are located on the door panels. Ground is supplied to the heated/cool seat switch through the low reference circuit and the respective door module. The door module plays an important part of the climate control seat operation, first by relaying the selected switch inputs to the MSM, and second, by controlling the mode and temperature indicators of the heated/cool seat switch.

When either a heat or cool seat switch is pressed, ground is applied through the switch contacts and the switch signal circuit to the door lock/window switch. In response to this signal, the door lock/window switch sends a serial data message to the MSM indicating the switch input. In response to this message, the MSM sends a pulse width modulation (PWM) signal through the appropriate heated/cool seat mode signal circuit to the seat ventilation heating and cooling modules indicating the heated or cooled seat request. The door lock/window switch then applies a ground through the appropriate heat or cool seat indicator control circuit to the switch illuminating the selected heat or cool mode indicator. At the same time, the door lock/window switch also applies a ground through the appropriate high, medium, or low temperature indicator control circuits illuminating temperature mode indicators.

Temperature Sensors

When the ignition is turned to the ON position, the heated and cooled seats initialize in the OFF state. With each activation of the heated or cool seat switch, the seat ventilation heating and cooling modules will cycle the temperature setting in the following manner: HIGH, LOW, and OFF.

When the ignition is turned to the ON position, the heated and cooled seats initialize in the OFF state. With each activation of the heated or cool seat switch, the seat ventilation heating and cooling modules will cycle the temperature setting in the following manner: HIGH, LOW, and OFF.

The seat cushion and seat back temperature sensors are each packaged with the seat heater elements. Each seat ventilation heating and cooling module supplies a 5 V reference voltage through the temperature sensor signal circuit and ground through the temperature sensor low reference circuit to the respective seat cushion and seat back temperature sensors. As the temperature of the seat changes, the resistance of the sensor varies changing the feedback voltage of the signal circuit. This voltage varies from 0.5-4 V. The ventilation modules monitor this voltage signal to determine the temperature of the seat so that it can adjust and maintain the seat temperature to the selected switch input.

Heated Seat Operation

The driver and passenger heated seats are controlled by the seat ventilation heating and cooling modules. When a heated seat switch is pressed, the seat ventilation heating and cooling modules apply battery positive voltage through the heater element supply voltage circuits and ground through the heater element low reference circuits to the seat heating elements. Then based on feedback from the seat temperature sensors, the ventilation modules control the seat temperature by cycling the power supply to the heater elements on and off in order to maintain the desired seat temperature.

Cooled Seat Operation and Blower Motors

As mentioned above in the heated/cool ventilation module description, the seat cushion and seat back blower motors are each packaged with the TED as an assembly. Each ventilation heating and cooling module contains logic that will allow for the blower to operate only when the ignition is in the ON position and only during cooled seat operation. When a cooled seat switch is pressed, the seat ventilation heating and cooling modules applies a pre-determined voltage to the TED and blower motor. Then based on the feedback from the seat temperature sensor, the ventilation module controls the applied voltage to the TEDs and blower motors in order to maintain the desired seat temperature.

With the cooled seat system, the speed of the blower motor is not related directly to the High, Med, or Low input from the heated/cool seat switch. The speed of the blower motor is related directly to TED temperature as described below in heated and cooled seat operation.