Electronic Manual Temperature Control

ELECTRONIC MANUAL TEMPERATURE CONTROL

The electronic manual temperature control (EMTC) components are used to select:
- air inlet source (outside or recirculated).
- blower motor speed.
- discharge air temperature (temperature blend).
- discharge air location (defrost, panel, floor).
- A/C compressor operation.

Control System Inputs
The EMTC system has two system control inputs.

Climate Control Assembly (EMTC Module)
The climate control assembly integrates the temperature control, airflow mode selection, A/C request button, recirculated air request button and rear defog switch into a single unit.

The temperature control switch setting determines air temperature. Movement of the temperature display from COOL (blue) to WARM (red) causes a corresponding movement of the temperature blend door(s) and determines the air discharge temperature that the air distribution system will maintain. The temperature control switch is an integral part of the climate control assembly and cannot be separately replaced.

The A/C request switch determines A/C compressor operation, except when the function selected is OFF, MAX or DEFROST. The A/C request switch is an integral part of the climate control assembly and cannot be separately replaced.

The recirculated air request button can select recirculated air in any mode except DEFROST and fresh air in any mode except MAX A/C and OFF. The rear defog button signals activation of the heated backlight.

The rear defog button is an integral part of the climate control assembly and cannot be installed separately.

The EMTC module is not equipped with self-test capabilities.

Blower Motor Switch
The blower motor switch is mounted in the climate control assembly and controls blower motor speed by adding or bypassing resistors in the blower motor resistor in all modes except OFF.

Control System Outputs
The EMTC system has three system outputs.

Blower Motor Resistor
The blower motor resistor:
- is located on the heater core and evaporator core housing near the blower motor.
- has three resistor elements mounted on the resistor board to provide four blower motor speeds.
- depending on the blower motor switch position, series resistance is added or bypassed in the blower motor circuit to decrease or increase blower motor speed.
- has an overheating device (thermal limiter) that will open the resistor when the temperature reaches approximately 220°C (428°F), interrupting the blower motor operation in all speeds except high.
- is serviced as an assembly. The thermal limiter cannot be reset and is not serviceable.

Temperature Blend Door Actuator(s)
The temperature blend door actuator(s):
- is located on the heater core and evaporator core housing.
- moves the temperature blend door(s) on command from the EMTC module.
- contains a reversible electric motor and a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the temperature blend door.
- applies a 5 volt signal to one end of the potentiometer and ground to the other. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the EMTC module and is matched with an expected wiper voltage value. The EMTC module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected EMTC module wiper voltage value.

Mode Door Actuators
The two mode door actuators:
- include the air inlet door and defrost/panel/floor mode door actuators.
- direct system airflow to the vehicle interior as determined by the climate control assembly.
- contains a reversible electric motor
- (defrost/panel/floor mode door actuator only) contains a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the mode door.
- (defrost/panel/floor mode door actuator only) apply a 5 volt signal to one end of the potentiometer and ground to the other. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the EMTC module and is matched with an expected wiper voltage value. The EMTC module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected EMTC module wiper voltage value.