From Automotive Wiki from mr-fix
Automatic air temperature
- HVAC unit will select proper air temperature to blow in order to reach and maintain temperature set by user. To do so it will consider factors like: current interior temperature, current exterior temperature, insolation, vehicle speed.
Automatic air distribution
- To achieve temperature set by user faster, HVAC unit can select which vents to use for better air mixing. If cars interior needs to be cooled down, then most likely windscreen vent is used. To warm up interior HVAC unit should direct more air through footwell vents.
Automatic fan speed
- Fan speed should be calculated based on the difference between current and desired temperature. The smaller the difference, the lower the fan speed.
- When doors or windows are open HVAC unit can decide that it will not use fan at high speeds knowing that desired temperature will not be reached.
- HVAC unit can have automatic fan speed limit adjustable by user.
- When temperatures selected for contiguous zones differ a lot HVAC unit should consider using lower fan speeds to prevent air mixing between zones.
- HVAC unit should consider coolant temperature as a factor when adjusting fan speed. On cold engine when in need of hot air it can wait additional minutes before increasing fan speed to make sure that the heat exchanger can produce desired temperature.
Limited fan speed
- HVAC controller can limit fan speed if the engine is not turned on to prevent fast battery discharge and eventual trouble with starting the car due to low electric power.
Zones and syncing
- HVAC units should have zone sync option that will help set the same temperature for all zones. This feature is most useful in cars with 4 and more zones.
- Based on the signal form the air quality sensor HVAC unit can decide to switch to recirculation in order to stop outside low quality air access cars interior.
- When switching into reverse HVAC unit can switch to recirculation to avoid sucking in exhaust gases that the car is about back-up into.
- HVAC unit can decide that after switching the engine off fan blower will not be turned off for few more minutes to remove excess humidity from the AC system.
- HVAC unit controls pressure in AC system so it can deliberately turn off the system in order to prevent it from further damage.
- HVAC unit should check how long ago AC system was used and turn it on for a while to make sure that system is properly lubricated.
Residual engine heat utilization
- After turning the engine off, user can press REST button which will reactive HVAC unit make it work as long as the engine heat can be used to keep interior temperature at desired level. Electrical water pump is required to keep coolant flowing through the system.
- Some cars are equipped with fuel-driven heater that can heat up coolant and engine oil. This helps the engine to reach its optional temperature more quickly to achieve maximum ecology and fuel efficiency
- Some cars are equipped with electrical coolant heater which helps engine reach optimal temperature faster.
- Some cars are equipped with electrical air heater to help heat up cars interior before coolant reaches desired temperature.
- Heating and ventilation features can be turned by remote or automatically according to user defined time table.
- By holding down the open key on the remote control you can open all windows and sunroof to ventilate the interior.
- Some makers are installing solar sun roof which is designed to power blower fan to keep interior cooler.
- By holding down the open key on the remote control you can open all windows and sunroof to ventilate cars interior.
- Few minutes after car was turned off and locked, HVAC module can decide to switch to recirculation. This will prevent bugs from entering the car through the air vents.