I believe the front defrost button is for the mirrors, not for the windshield. The windshield defrost is typically activated via the HVAC system.
heated mirrors are activated with the rear window defroster. i can find nothing as to defrost front windshield with auto start.
Front Defrost Button
Press and release the touchscreen button, or push and release the button on the faceplate, to
change the current airflow setting to Defrost mode. The indicator illuminates when this feature
is on. Air comes from the windshield and side window demist outlets. When the defrost button
is selected, the blower level may increase. Use Defrost mode with maximum temperature settings
for best windshield and side window defrosting and defogging. When toggling the front
defrost mode button, the climate system will return to previous setting.
Rear Defrost Button
Push and release the button on the touchscreen, or push and release the button on the faceplate,
to turn on the rear window defroster and the heated outside mirrors (if equipped). An indicator
will illuminate when the rear window defroster is on. The rear window defroster automatically
turns off after ten minutes.
also:
Automatic Temperature Control (ATC) — If Equipped Automatic Operation
1. Push the AUTO button on the faceplate, or the AUTO button on the touchscreen on the Automatic Temperature
Control (ATC) Panel.
2. Next, adjust the temperature you would like the system to maintain by adjusting the driver and passenger
temperature control buttons. Once the desired temperature is displayed, the system will achieve and automatically
maintain that comfort level.
3. When the system is set up for your comfort level, it is not necessary to change the settings. You will experience
the greatest efficiency by simply allowing the system to function automatically.
NOTE:
• It is not necessary to move the temperature settings for cold or hot vehicles. The system automatically adjusts
the temperature, mode, and blower speed to provide comfort as quickly as possible.
• The temperature can be displayed in U.S. or Metric units by selecting the US/Metric customer-programmable feature.
Refer to the “Uconnect Settings” in “Multimedia” for further information.
To provide you with maximum comfort in the Automatic mode during cold start-ups, the blower fan will remain on
low until the engine warms up. The blower will increase in speed and transition into Auto mode.