Windshield Temperature and Inside Moisture Sensor
The relative humidity sensor measures the relative humidity of the compartment side of the windshield. It also detects the temperature of the windshield surface on the passenger compartment side. Both values are used as control inputs for the HVAC control module application to calculate the fog risk on windshield compartment side and ability to reduce fuel consumption by decreasing A/C compressor power to a minimum without causing any fog. The sensor will also enable partial recirculation mode in order to improve heat-up performance of the passenger compartment under cold ambient temperature conditions without the risk of mist build-up on the windshield. The humidity sensor element temperature sensor supplies the temperature of the humidity sensor element.
A/C Compressor
The AC compressor function is to provide refrigerant flow in the AC refrigerant loop to help cool down the cabin, help dehumidify the air in a defrost mode and help maintain the battery temperature. Rather than a more-typical pulley, the A/C compressor uses a 3-phase alternating current, high voltage electric motor to operate. It has an on-board inverter that takes high voltage direct current from the vehicle's high voltage battery and inverts it to alternating current for the motor. The AC compressor shall be activated when any of the three following events occur:
- The customer pushes the AC button or
- The HVAC control, in ECO climate or Comfort Climate Settings, requests the electric AC compressor on to help in cooling the cabin or removing moisture in conditions where the windows may fog or
- The hybrid/EV powertrain control module 2 requests the AC compressor on to help maintain the battery temperature
The hybrid/EV powertrain control module 2 uses values from the A/C refrigerant pressure sensor, A/C refrigerant thermistor, duct temperature sensors, ambient air temperature sensor , passenger compartment temperature sensor, evaporator temperature sensor, battery cell temperature sensors, battery coolant temperature sensors and battery coolant pumps to determine the speed at which the compressor will operate. This message is sent from the hybrid/EV powertrain control module 2 to the A/C compressor control module via serial data message.
Air Delivery
The HVAC control module controls the distribution of air within the passenger compartment by the use of the mode actuator. The modes that may be selected are:
- Defrost
- Defog
- Panel
- Floor
- BiLevel
In auto mode, the air delivery mode is controlled automatically based on cooling/warming needs of the compartment. The desired air distribution mode can be selected with the air distribution buttons at the HVAC faceplate control. The HVAC control delivers the values to the HVAC control module via serial data. The HVAC control module controls the mode actuator so that it drives the flap to the calculated position. Depending on the position of the flap, air is distributed through various ducts leading to the outlets in the dash. Turning the mode flap to the defrost position, the HVAC control module will move the recirculation actuator to outside air, reducing window fogging. When defrost is selected, the blower motor will be activated. The HVAC control module enables a high volume of air delivered to the front defrost vents. A/C is available in all modes.
Recirculation Operation
The recirculation button is part of the HVAC faceplate control. The selected recirculation button position is sent to the HVAC control module via serial data. The HVAC control module controls the air intake through the recirculation actuator. The recirculation switch closes and opens the recirculation flap in order to circulate the air within the vehicle, or route outside air into the vehicle.
Inside air recirculation is prevented if the defrost mode is not active. When the defrost mode is active, the recirculation actuator opens the recirculation flap and outside air is circulated to the windshield to reduce fogging.
In automatic recirculation mode the values of the windshield temperature and inside moisture sensor are used as control inputs for the HVAC control module application to calculate the fog risk on the passenger compartment side of the windshield. The A/C compressor and the defrost mode are activated to prevent or remove fog on the passenger compartment side of the windshield.
Automatic Operation
The user can select to operate the Blower, Recirculation and Air Delivery operations in auto per auto operation mode.
To put the HVAC system in full automatic mode, the following is required:
The auto button must be pressed.
The system indicates that all 3 functions are being operated automatically by lighting the auto button LED.
When the auto button is pressed, the system responds by putting the blower, air delivery and recirculation into auto mode. If any of these functions are adjusted then the auto button indication shall go off and the function will leave auto operation and follow the user requested setting: auto, blower, air delivery and recirculation. In this setting the blower request is adjusted to quickly heat the cabin initially. After comfort is reached, the blower is mimized to reduce noise and temperature drifts.
Under cold ambient temperatures, the automatic HVAC system provides heat in the most efficient manner. The operator can select an extreme temperature setting but the system will not warm the vehicle any faster. Under warm ambient temperatures, the automatic HVAC system also provides air conditioning in the most efficient manner. Selecting an extreme cool temperature will not cool the vehicle any faster.
In automatic mode the values of the windshield temperature and inside moisture sensor are used as control inputs for the HVAC control module application to calculate the fog risk on the passenger compartment side of the windshield and ability to reduce fuel consumption by decreasing A/C compressor power to a minimum without causing any fog. The A/C compressor and the defrost mode may be activated to prevent or remove fog on the passenger compartment side of the windshield. The sensor will also enable partial recirculation mode in order to improve heat-up performance of the passenger compartment under cold ambient temperature conditions without the risk of mist build-up on the windshield.
