Part 1
Climate Control - EMTC
Component Location
Overview
The EMTC (Electronic Manual Temperature Control) system heats or cools the vehicle depending on the HVAC (Heating, Ventilation, and Air Conditioning) control panel selection.
- The control panel selection determines heating or cooling, air distribution and enables blower motor operation.
- The temperature control setting determines the outlet air temperature.
- The blower motor switch varies the blower motor speed.
- During A/C (Air Conditioning) operation, the system reduces the relative humidity of the air inside the vehicle.
System Operation
System Diagram
Network Message Chart
Module Network Input Messages - FCIM (Front Controls Interface Module)
Module Network Input Messages - PCM (Powertrain Control Module)
Module Network Input Messages - HVAC (Heating, Ventilation, and Air Conditioning) Module
The Refrigerant Cycle
During stabilized conditions ( A/C (Air Conditioning) system shutdown), the refrigerant pressures are equal throughout the system. When the A/C (Air Conditioning) compressor is in operation, it uses a piston pump to compress the cool vapor, causing it to become high-temperature/high-pressure vapor. The high-temperature/high-pressure vapor is then released into the top of the A/C (Air Conditioning) condenser core.
The A/C (Air Conditioning) condenser, being close to ambient temperature, causes the refrigerant vapor to condense into a liquid when heat is removed from the refrigerant by ambient air passing over the fins and tubing. The now liquid refrigerant, still at high pressure, exits from the bottom of the A/C (Air Conditioning) condenser and enters the inlet side of the A/C (Air Conditioning) receiver/drier (integral to the condenser). The receiver/drier is designed to remove moisture and contaminants from the refrigerant system.
The outlet of the receiver/drier is connected to the TXV (Thermostatic Expansion Valve). The TXV (Thermostatic Expansion Valve) provides the orifice which is the restriction in the refrigerant system and separates the high and low pressure sides of the A/C (Air Conditioning) system. As the liquid refrigerant passes across this restriction, its pressure and boiling point are reduced. An internal temperature sensing bulb senses the temperature of the refrigerant flowing out of the evaporator core and adjusts an internal pin-type valve to meter the refrigerant flow into the evaporator core. The internal pin-type valve decreases the amount of refrigerant entering the evaporator core at lower temperatures and increases the amount of refrigerant entering the evaporator core at higher temperatures.
The liquid refrigerant is now at its lowest pressure and temperature. As it passes through the A/C (Air Conditioning) evaporator, it absorbs heat from the airflow passing over the plate/fin sections of the A/C (Air Conditioning) evaporator. This addition of heat causes the refrigerant to boil (convert to gas). The now cooler air can no longer support the same humidity level of the warmer air and this excess moisture condenses on the exterior of the evaporator coils and fins and drains outside the vehicle.
The refrigerant cycle is now repeated with the A/C (Air Conditioning) compressor again increasing the pressure and temperature of the refrigerant.
A thermistor which monitors the temperature of the air that has passed through the evaporator core controls A/C (Air Conditioning) clutch cycling. If the temperature of the evaporator core discharge air is low enough to cause the condensed water vapor to freeze, the A/C (Air Conditioning) clutch is disengaged by the PCM (Powertrain Control Module).
The high-side line pressure is also monitored so that A/C (Air Conditioning) compressor operation will be interrupted if the system pressure becomes too high or is determined to be too low (low charge condition).
The A/C (Air Conditioning) compressor relief valve will open and vent refrigerant to relieve unusually high system pressure.
Controls and Compressor Cycling
The EMTC (Electronic Manual Temperature Control) system uses inputs from the FCIM (Front Controls Interface Module) to provide the interface for the vehicle occupants to control the climate control system. When selections are made, the FCIM (Front Controls Interface Module) communicates the selections to the HVAC (Heating, Ventilation, and Air Conditioning) module, which adjusts the climate control system components to achieve the desired state. When the climate control system is operating in AUTO mode, the required climate control system settings are determined by the HVAC (Heating, Ventilation, and Air Conditioning) module. The HVAC (Heating, Ventilation, and Air Conditioning) module then adjusts the climate control system components to the desired state.
The HVAC (Heating, Ventilation, and Air Conditioning) module utilizes a FET (Field-Effect Transistor) protective circuit strategy for its actuator outputs. Output load (current level) is monitored for excessive current (typically short circuits) and is shut down (turns off the voltage or ground provided by the module) when a fault event is detected. For additional information on HVAC (Heating, Ventilation, and Air Conditioning) module FET (Field-Effect Transistor) protection, REFER to Heating Ventilation Air Conditioning (HVAC) Module - Electronic Manual Temperature Control (EMTC).
The PCM (Powertrain Control Module) monitors the discharge pressure measured by the A/C (Air Conditioning) pressure transducer. The PCM (Powertrain Control Module) interrupts A/C (Air Conditioning) compressor operation in the event the A/C (Air Conditioning) pressure transducer indicates high system discharge pressures. It is also used to sense low charge conditions. If the pressure is below a predetermined value for a given ambient temperature, the PCM (Powertrain Control Module) will not allow the A/C (Air Conditioning) clutch to engage.
The HVAC (Heating, Ventilation, and Air Conditioning) module maintains evaporator core temperature and prevents icing of the evaporator core by measuring the temperature of the airflow immediately after the evaporator core. It does this by switching the A/C (Air Conditioning) request signal off before the evaporator temperatures are cold enough to freeze the condensation and by switching the A/C (Air Conditioning) request signal on when the evaporator temperature rises above acceptable levels.
When battery voltage is applied to the A/C (Air Conditioning) compressor clutch field coil, the clutch disc and hub assembly is drawn toward the A/C (Air Conditioning) clutch pulley. The magnetic force locks the clutch plate and hub assembly and the A/C (Air Conditioning) clutch pulley together as one unit, causing the compressor shaft to rotate. When battery voltage is removed from the A/C (Air Conditioning) compressor clutch field coil, springs in the clutch plate and hub assembly move the clutch plate away from the A/C (Air Conditioning) clutch pulley.
For more information on compressor operation, REFER to Air Conditioning (AC) Compressor.
Air Handling
Based on the climate control system settings the heater core and evaporator core housing directs airflow through the evaporator core and the heater core as needed, with the airflow exhausting through the appropriate outlets. Door actuators control the internal doors of the heater core and evaporator core housing to direct the airflow as selected by the climate control system settings. The air source is from outside air or recirculated passenger compartment air as determined by the air inlet mode door position.
The defrost/panel/floor mode door, temperature blend door and air inlet mode door actuators use a potentiometer to sense and communicate the door position to the HVAC (Heating, Ventilation, and Air Conditioning) module.When an airflow mode, desired driver or passenger temperature, or fresh air or recirculation mode is requested by the HVAC (Heating, Ventilation, and Air Conditioning) module the appropriate door actuator motor(s) is driven to the desired position, using the position sensed by the door actuator potentiometer to accurately position the door actuator.
The HVAC (Heating, Ventilation, and Air Conditioning) module will adjust the air inlet door depending on the humidity measured by the in-vehicle temperature and humidity sensor. If the vehicle cabin becomes too humid and recirculated air is not selected, the HVAC (Heating, Ventilation, and Air Conditioning) module will adjust the air inlet door to allow more recirculated air. When the humidity level drops, it will adjust back to fresh air. The HVAC (Heating, Ventilation, and Air Conditioning) module will also make system adjustments based on in-vehicle temperature.
The HVAC (Heating, Ventilation, and Air Conditioning) module uses the blower motor speed control to control the blower speed. REFER to Blower Motor Speed Control.
Control System Logic
Climate Control System Network Communication
The controls for the climate control system are located in the FCIM (Front Controls Interface Module).
The FCIM (Front Controls Interface Module) reads the climate control selections and sends the requests to the HVAC (Heating, Ventilation, and Air Conditioning) module in the following message path:
- The FCIM (Front Controls Interface Module) sends the requests over the I-CAN (Infotainment Controller Area Network) to the IPC (Instrument Panel Cluster).
- The IPC (Instrument Panel Cluster) then relays the requests to BCM (Body Control Module) over the HS-CAN (High Speed Controller Area Network).
- Lastly, the BCM (Body Control Module) then sends the requests to the HVAC (Heating, Ventilation, and Air Conditioning) module over the MS-CAN (Medium Speed Controller Area Network).
The messaging path is followed in reverse for any status updates that need to be sent from the HVAC (Heating, Ventilation, and Air Conditioning) module to the FCIM (Front Controls Interface Module).
When an airflow mode, fresh air or RECIRC mode, temperature setting or blower speed is selected, the FCIM (Front Controls Interface Module) sends this selection to the HVAC (Heating, Ventilation, and Air Conditioning) module using the message path described above.
When A/C is selected, the FCIM (Front Controls Interface Module) sends the selection to the HVAC (Heating, Ventilation, and Air Conditioning) module using the message path described above. If the ambient temperature is sufficient, the HVAC (Heating, Ventilation, and Air Conditioning) module then sends the request to the BCM (Body Control Module) over the MS-CAN (Medium Speed Controller Area Network). The BCM (Body Control Module) then sends the request to the PCM over the HS-CAN (High Speed Controller Area Network).
MAX AC
When MAX A/C (Air Conditioning) is selected:
- the air inlet door closes, preventing outside air and admits only recirculated air.
- the RECIRC indicator is illuminated (RECIRC forced on).
- the mode doors direct airflow to the instrument panel registers.
- the temperature blend doors move to the full cool position. Blended air temperature is available.
- the A/C (Air Conditioning) request button is illuminated.
- the A/C (Air Conditioning) compressor operates if the outside temperature is above approximately 6 C (42.8 F).
- the blower motor is commanded to the highest speed. The blower motor speed is adjustable.
PANEL
When PANEL is selected:
- the RECIRC request button is enabled. If the RECIRC request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
- the mode doors direct airflow to the instrument panel registers.
- blended air temperature is available. Only when A/C (Air Conditioning) compressor operation has been selected by pressing the A/C (Air Conditioning) request button (indicator on) can the airflow temperature be cooled below the outside air temperature.
- the A/C (Air Conditioning) request button is enabled. The A/C (Air Conditioning) compressor operates and the indicator illuminates if the A/C (Air Conditioning) request button is selected and the outside temperature is above approximately 6 C (42.8 F).
- the blower motor is on.
PANEL-FLOOR
When PANEL/FLOOR is selected:
- the RECIRC request button is enabled. If the RECIRC request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
- the mode doors direct airflow to the floor duct and the instrument panel registers. A small amount of airflow from the side window demisters and defrost duct is present.
- blended air temperature is available. Only when A/C (Air Conditioning) compressor operation has been selected by pressing the A/C (Air Conditioning) request button (indicator on) can the airflow temperature be cooled below the outside air temperature.
- the A/C (Air Conditioning) request button is enabled. The A/C (Air Conditioning) compressor operates and the indicator illuminates if the A/C (Air Conditioning) request button is selected and the outside temperature is above approximately 6 C (42.8 F).
- the blower motor is on.
OFF
When OFF is selected:
- the air inlet door closes, preventing outside air and allowing only recirculated air.
- the blower motor is off.
FLOOR
When FLOOR is selected:
- the RECIRC request button is enabled. If the RECIRC request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
- the mode doors direct airflow to the floor duct. A small amount of airflow from the defroster duct and side window demisters is present.
- blended air temperature is available. Only when A/C (Air Conditioning) compressor operation has been selected by pressing the A/C (Air Conditioning) request button (indicator on) can the airflow temperature be cooled below the outside air temperature.
- the A/C (Air Conditioning) request button is enabled. The A/C (Air Conditioning) compressor operates and the indicator illuminates if the A/C (Air Conditioning) request button is selected and the outside temperature is above approximately 6 C (42.8 F).
- the blower motor is on.
FLOOR-DEFROST
When FLOOR/DEFROST is selected:
- the RECIRC request button is enabled. If the RECIRC request button is selected (indicator on), the air inlet door closes, preventing outside air from entering the passenger compartment. If the RECIRC request button is not selected (indicator off), the air inlet door opens, allowing only outside air into the passenger compartment.
- the mode doors direct airflow to the floor duct, the defroster duct and the side window demisters.
- blended air temperature is available.
- the A/C (Air Conditioning) request button toggles the indicator on and off. To reduce fogging, the A/C (Air Conditioning) compressor operates automatically, regardless of indicator status, if the outside temperature is above approximately 6 C (42.8 F).
- the blower motor is on.
DEFROST
When DEFROST is selected:
- the RECIRC request button is disabled. The air inlet door opens, allowing only outside air into the passenger compartment.
- the mode doors direct airflow to the defroster duct and side window demisters. A small amount of airflow from the floor duct is present.
- blended air temperature is available.
- the A/C (Air Conditioning) request button toggles the indicator on and off. To reduce fogging, the A/C (Air Conditioning) compressor operates automatically, regardless of indicator status, if the outside temperature is above approximately 6 C (42.8 F).
- the blower motor is on.