Control System Outputs - Electronic Manual Temperature Control (EMTC)

Blower Motor Resistor 

The blower motor switch varies the blower motor ground circuit resistance by adding or bypassing series resistance in the blower motor resistor. Increased resistance lowers the blower motor speed, and lowered resistance increases blower motor speed. When the blower motor is in the HIGH position, the blower motor resistor is bypassed.

The blower motor resistor is located on the heater core and evaporator core housing near the blower motor.

Temperature Door Actuator 

The temperature door actuator moves the temperature door on command from the HVAC control module.

The temperature door actuator contains a reversible electric motor and a potentiometer. The potentiometer circuit consists of a 5-volt reference signal connected to one end of a variable resistor, and a signal ground connected to the other. A signal circuit is connected to a contact wiper, which is driven along the variable resistor by the actuator shaft. The signal to the HVAC control module from the contact wiper indicates the position of the temperature door. The HVAC control module powers the actuator motor to move the temperature door to the desired position. The vehicle occupants use the temperature selector knob to set the desired position.

The temperature door actuator is located on the top of the heater core and evaporator core housing.

Defrost/Panel/Floor Mode Door Actuator 

The defrost/panel/floor mode door actuator uses a cam and lever assembly to position the defrost/panel/floor mode doors on command from the HVAC control module. The defrost/panel/floor mode door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC control module to monitor the position of the defrost/panel/floor mode doors. The potentiometer circuit consists of a 5-volt reference signal connected to one end of a variable resistor, and a signal ground connected to the other. A signal circuit is connected to a contact wiper, which is driven along the variable resistor by the actuator shaft. The signal to the HVAC control module from the contact wiper indicates the position of the defrost/panel/floor mode doors. The HVAC control module powers the actuator motor to move the defrost/panel/floor mode doors to the desired position. The vehicle occupants use the mode selector rotary switch to set the desired position.

Air Inlet Mode Door Actuator 

The air inlet mode door actuator contains a reversible electric motor. The HVAC control module powers the actuator motor to the full RECIRC or full FRESH air inlet position, and does not require a potentiometer circuit to monitor its position.