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 heated/cool ventilation module
* Seat back heated/cool ventilation module
* Memory seat module
* Climate Control Seat Module
* Heated/cooled seat switches and HVAC control module (Escalade)
* Heated/cooled seat switch and door lock/window switch (Chevrolet and GMC)

Air Circulation

When the heated/cool seat switch is pressed to initiate operation of the climate control seat system, cabin air is drawn through the heated/cool ventilation 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 climate control 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 climate control seat system operation.

Seat Heat/Cool Ventilation Module

Each heated/cool seat has 2 heat/cool ventilation modules, one located under the seat cushion and one located in the seat back. These modules are controlled by the CCSM. Each ventilation module contains a thermo-electric device (TED), a temperature sensor, and a blower motor. The TED and temperature sensor are 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 heat exchange. The air flowing past these fins is either 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 heat or 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. When the polarity of the current flow to the TEDs is switched, the hot and cool sides of the TED reverse.

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

Climate Control Seat System

The climate control seat system consists of 2 heated/cool ventilation modules and one CCSM that controls both the driver and passenger heated/cool seats systems. The CCSM is mounted below the front passenger seat cushion.

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 TED located under the seat cushion and in the seat back. The air is either heated or 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 CCSM uses a set of algorithms to control the temperature of the selected heating or cooling modes.

Climate Control Seat Module Power and Ground

Battery positive voltage is supplied at all times to the CCSM through the battery positive voltage circuit and a 30 A fuse that is located in the I/P fuse block. This voltage is used by the CCSM to supply power to the TEDs and the blower motors. Ignition voltage is also supplied to the CCSM through the ignition voltage circuit and a 10 A fuse located in the underhood fuse block. The ignition voltage is used to power up the CCSM and allows the climate control seat system to operate only with the ignition in the ON position. The CCSM is grounded through the module ground circuit and G304.

Climate Control Seat Module

The 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.

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 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.

Modes of Operation

There are 3 modes available for climate control seat system operation, heated seat, cool seat, and back only heat operation. When a heat or cool seat mode signal request is received, the CCSM will activate both the seat cushion and seat back ventilation modules. When the seat BACK ONLY mode button is pressed once, the CCSM will deactivate the seat cushion ventilation module and leave the seat back ventilation module ON. Press the BACK ONLY mode button a second time and the CCSM will re-activate the seat cushion ventilation module.

Heated/Cooled Seat Switches and HVAC Control Module (Escalade)

The heated and cooled seat system is controlled through 3 different switch inputs of the HVAC control module. When one of the switches is pressed, the HVAC control module 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 heated/cool seat mode signal circuit to the CCSM indicating the heated or cooled seat request. During heated or 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 determined by a serial data message from the MSM.

Heated/Cooled Seat Switch and Door Lock/Window Switch (Chevrolet and GMC)

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 then sends a pulse width modulation (PWM) signal through the appropriate heated/cool seat mode signal circuit to the CCSM 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

As mentioned above in the heated/cool ventilation module description, the seat cushion and seat back temperature sensors are each packaged with a TED and blower motor as an assembly. The seat temperature sensors are thermistors which are attached directly to the fins of each TED. The CCSM 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 TED changes, the resistance of the thermistor varies changing the feedback voltage of the temperature sensor signal circuit. This voltage varies from 0.5 - 4 V. The CCSM monitors this voltage signal to determine the fin temperature so that it can adjust and maintain the seat temperature to the selected switch input.

Blower Motors

Also, as mentioned above in the heated/cool ventilation module description, the seat cushion and seat back blower motors are each packaged with a TED and temperature sensor as an assembly. Each blower motor contains logic that will allow for the blower to operate only when the ignition is in the ON position. When the ignition is ON and the CCSM is powered up, the module supplies battery positive voltage through the blower supply voltage circuit to the logic of the blower motors. When the heated/cool seat switch is pressed, the CCSM applies a pre-determined voltage through the blower speed control circuits to the blower motors. The module also supplies each blower motor with a ground path through the blower low reference circuits.

With the climate control 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.

Heated Seat Operation

When the heated seat switch is pressed for High Heat, the CCSM will transition to the HEAT state. In the heat state, the CCSM applies a pre-determined voltage through the ventilation module heat control circuits to the heat side of the TEDs, while providing a ground through the ventilation module cool control circuit to the cool side of the TEDs. A pre-determined voltage is also applied to the blower motors. The CCSM uses the following sequence beginning with the Heat SoftStart Mode to achieve the set point temperature before it can enter the Control Heat Mode. If the seat temperature is already above the Temperature Set Point, the CCSM will skip the Heat SoftStart Mode and proceed to the Control Heat Mode.

* Heat SoftStart Mode-While in transition to the heat mode, the CCSM will initiate the SoftStart Mode. The intent of the Heat SoftStart Mode is for the module to bring the ventilation module fin temperature up to the pre-determined Temperature Set Point of the Max Heat Mode. The module does this by setting the blower motor speed control to a pre-determined voltage while ramping up the ventilation module voltage from 0 volts to the maximum voltage, not to exceed 5 seconds, at which point the system transitions to Max Heat Mode. The Heat SoftStart Mode will only be attempted once per ignition cycle.
* Max Heat Mode-Upon completion of the Heat SoftStart Mode, the CCSM will initiate Max Heat Mode. The intent of the MAX Heat Mode is to maintain the fin temperature to the pre-determined Temperature Set Point in order for the CCSM to go into the Control Heat Mode. The CCSM does this by maintaining the TED at the maximum voltage while maintaining the minimum required airflow across the fins. After max heat duration has been reached, or upon achieving the pre-determined Temperature Set Point, the system transitions to the Control Heat Mode.
* Control Heat Mode-At the completion of Max Heat Mode, the CCSM will initiate Control Heat Mode. The intent of the Control Heat Mode is to maintain the desired fin temperature or the set point temperature. The CCSM does this in two ways; first by adjusting the voltage supply to the blower motor to control blower motor speed, then secondly by controlling the voltage supplied to the TED. The CCSM updates these voltages once every second. Increasing the blower motor speed will decrease the fin temperature. If the maximum blower motor speed is achieved and the fin temperature is still above the set point of high heat, the CCSM will then begin to control the TED voltage to achieve Temperature Set Point. Decreasing the TED voltage decreases the fin temperature. If the CCSM is trying to raise the fin temperature to set point by using TED voltage, and the fin temperature cannot be raised because the TED voltage is at the maximum, the CCSM reduces the blower motor speed to achieve the Temperature Set Point.

Cooled Seat Operation

When the cool seat switch is pressed for High Cool, the CCSM will transition to the COOL state. In response to this command, the CCSM applies a pre-determined voltage through the ventilation module cool control circuits to the cool side of the TEDs while providing a ground through the ventilation module heat control circuits to the heat side of the TEDs. A pre-determined voltage is also applied to the blower motors. The CCSM uses the following sequence, beginning with the Cool SoftStart Mode, to achieve the set point temperature before it can enter the Open Loop Cool Mode.

* Cool SoftStart Mode-The intent of the Cool SoftStart Mode is for the CCSM to bring the TED fin temperature to maximum cool temperate. The CCSM does this by setting the blower motor speed control voltage to 0 volts, while ramping up the TED voltage duty cycle from 0 volts to maximum voltage duty cycle over a period not to exceed 5 seconds. Then, with the TEDs at maximum voltage, the CCSM will increase the blower speed to maximum voltage, and keep these settings for the MAX COOL DURATION. After which the system transitions to the Open Loop Cool Mode.
* Open Loop Cool Mode-At the completion of Cool SoftStart Mode, the CCSM will initiate Open Loop Cool Mode. The intent of this mode is to maintain the set point fin temperature based on the input of the cool seat switch. First, by controlling the speed of the blower motor, then secondly, by controlling TED voltage. The CCSM updates these voltages once every second.

Fault State

The climate control seat system will operate normally in the battery voltage range of 9-16 volts. If the system voltage falls outside of this voltage range, the module will shut down all outputs until the system returns to its normal operating voltage range. The system will also transition to the fault state per the conditions listed below, by shutting down all outputs for the seat in which the fault occurred.

High Temperature Fault State

During the heating or cooling modes, if the TED temperatures listed below are exceeded for more than 4 seconds, the system will enter the High Temperature Fault State. At which time the CCSM will set the TED voltage duty cycle to 0%, set the blower speed control to maximum voltage to blow ambient air over the TEDs, attempting to reduce the TED temperature below the listed maximums. The system will operate in this mode for 30 seconds. If the over temperature fault still exists after 30 seconds, the system will transition to the FAULT state for the remainder of the ignition cycle. If the over temperature fault clears, the system will then transition to the appropriate heat or cool softstart mode. The following temperatures are based upon individual readings of either sensor:

* Heat mode TED temperature exceeds 230°F (110°C).
* Cool mode TED temperature exceeds 149°F (65°C).

Temperature Delta Fault

During the heating or cooling modes, if the CCSM detects a temperature difference between the seat cushion and seat back TED temperature sensors exceeding the delta temperature listed below for more than 4 seconds, the system will enter the Temperature Delta Fault state. At which time the CCSM will set the TED voltage duty cycle to 0%, set the blower speed control to maximum voltage to blow ambient air over the TEDs, attempting to reduce the delta temperature to less than 68°F. The system will operate in this mode for 30 seconds. If the delta temperature fault still exists after 30 seconds, the system will transition to the FAULT state and remain there until the ignition has been set to OFF.

* Delta between the seat cushion and seat back temperature sensors is 104°F (40°C).
* This fault state is disabled in the back only mode.