Dual-Zone Electronic Automatic Temperature Control (EATC)

WARNING: This page is about a different car, the 2015 Lincoln MKT. However, it is still accessible from the selected car via links, so may be relevant.

The HVAC module analyzes input from the following major sources:

Temperature, airflow direction, blower, A/C and RECIRC selection (made by the vehicle occupants)
In-vehicle temperature/humidity sensor
AAT sensor
Autolamp/sunload sensor
Vehicle speed
Engine coolant temperature

Using these inputs, the dual-zone HVAC module determines the correct conditions for the following outputs:

A/C compressor operation
Blower motor speed
RH and LH temperature blend door positions
Defrost/panel/floor mode door position
Air inlet mode door position

Control System Inputs

The dual-zone EATC system has 4 control system inputs.

HVAC Module

The dual-zone EATC system uses a remote HVAC module that is separate from the control interface. The FCIM provides the interface for the vehicle occupants to control the climate control system. When selections are made, the FCIM communicates the selections to the HVAC module through the vehicle module communication network. The remote dual-zone HVAC module controls the climate control system based on the FCIM selections or automatically controls the climate control system in the AUTO mode.

In-Vehicle Temperature/Humidity Sensor

The in-vehicle temperature/humidity sensor contains 2 thermistors which separately measure the in-vehicle air temperature and humidity and send those readings to the HVAC module. The in-vehicle temperature/humidity sensor has an electric fan within the sensor that draws in-vehicle air across the thermistors.

Autolamp/Sunload Sensor (Light Sensor)

The autolamp/sunload sensor supplies information to the dual-zone HVAC module to lower the A/C temperature output in the vehicle's cabin, cooling the vehicle interior and occupants.

The autolamp/sunload sensor is also used by the exterior lighting system for autolamp operation. For removal and installation of the autolamp/sunload sensor, refer to Light Sensor in Exterior Lighting .

AAT Sensor

The AAT sensor signal is received by the dual-zone HVAC module over the vehicle module communication network from the PCM.

For information regarding the outside air temperature display, refer to Instrumentation, Message Center, and Warning Chimes

Control System Outputs

The EATC system has 4 control system outputs. When operating in AUTO mode, the control system outputs are automatically adjusted by the HVAC module.

NOTE: Each of the 4 control system outputs may be overridden by the passenger if desired.

Blower Motor Speed

The HVAC module controls the blower speed by sending a PWM signal to the blower motor speed control. The blower motor speed control provides variable ground feed for the blower motor to control the speed. A delay function provides a gradual increase or decrease in blower motor speed under all conditions.

The blower motor speed control has internal temperature and surge protection. In the event of excessive blower motor supply voltage or current draw, or if the blower motor speed control temperature climbs considerably due to a failure event (such as a seized or partially-seized blower motor), the blower motor speed control automatically shuts down the blower motor. After shutdown, the blower motor speed control attempts to restart every 120 seconds until the blower motor can be safely operated.

Temperature Blend Door Position

The dual-zone EATC system uses 2 temperature blend door actuators to control 2 separate temperature blend doors. The temperature blend doors independently vary the LH side and RH side temperature settings, as desired. The temperature blend door actuators each contain 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 module from the contact wiper indicates the position of the temperature blend door. The HVAC module powers the actuator motors to move the temperature blend doors to the desired positions. The desired temperature blend door positions are calculated by the HVAC module based on the set temperature, in-vehicle temperature, ambient air temperature and sunload.

Defrost/Panel/Floor Mode Door Position

Airflow through the HVAC plenum is controlled by the defrost/panel/floor mode door actuator. The defrost/panel/floor mode door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC module to monitor the position of the defrost/panel/floor mode door. 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 module from the contact wiper indicates the position of the defrost/panel/floor mode door. The HVAC module powers the actuator motor to move the defrost/panel/floor mode door to the desired position. The desired position is set by the vehicle occupants using the mode selector buttons.

Air Inlet Mode Door Position

The air inlet mode door actuator contains a reversible electric motor and potentiometer. The potentiometer allows the HVAC module to monitor the position of the air inlet mode door. The HVAC module adjusts the air inlet door depending on the humidity measured by the in-vehicle temperature/humidity sensor. If the vehicle cabin becomes too humid and recirculated air is not selected, the HVAC module adjusts the air inlet door to allow more recirculated air. When the humidity level drops, it adjusts back to fresh air.