In MY15 Golf GTE, the system works on the principle that the LED only only lights up when a button/option/fan speed is selected. It is confusing because if I select "OFF" button (meaning the HVAC system is fully turned of), the LED above it will be ON.
On my 2015 model, pressing the Auto button when the Air Con LED is off will turn on the Air Con LED on as well as the Auto LED (if this was also not lit).
NB: In my opinion if the Air Con LED is on, then the air passes through the compressor (and is thus cooled and dried), regardless of the outside temperature, before being warmed if necessary and circulated in the car. As such it helps demist and keep the windows clear in cold weather.
What I can't work out is when/if the central two vents are used when the system is in Auto mode!
The air cooling mode is switched on/off when the A/C button is pressed. When the air cooling is switched off, the air is neither cooled nor dehumidified. The windows may mist up as a result. The air cooling is switched off automatically at low outside temperatures.
I now recall the compressor on the Climate Control on my 1998 A4 didn't operate (I think) at the temperature when the snowflake was displayed (or lower) - typically you are left to guess the temperature with the A3 e-tron (just "low" being stated but not defined). Incidentally the Climate Control doesn't operate at all now on my 1998 A4 since the compressor broke and the dealer tried to rip me off another £800 after charging me £300 and just replacing the belt
The on-line handbook also contains the following:
AUTO Switching automatic mode on/off
The automatic mode is switched on when the AUTO button is pressed. The AUTO mode is switched off immediately when you operate any of the manual air controls. The automatic mode maintains a constant temperature inside the vehicle. Air temperature, output and distribution are regulated automatically. The "eco" mode*1) is activated if you press the AUTO button briefly while automatic mode is active. Fuel is saved in "eco" mode* because the settings respond more passively. The "eco" mode* is on when eco appears in the console display. The "eco" mode* is deactivated when you press the AUTO button again.
1) This function is not available on all export versions.
Must try playing with the buttons tomorrow and seeing if I have one of the export versions with the eco mode enabled...
Synchronisation: By pressing the AUTO button for 2 seconds, the temperature of the passenger's side can be set to the temperature of the driver's side. The settings remain synchronised until the temperature is changed on the passenger's side.
"Briefly" (in earlier quotes) must be less than 2 seconds
Here's another one to test:
If the engine is cold, the air conditioner will automatically switch to air recirculation mode when the vehicle is reversing.
Once you've sussed out what "cold" means...and then, how do you know it's switched so?
Huh-huh. You know, I faced the same problem as you when I didn't know how to repair it. Turns out that it was problem of the electricity (it was not enough). So I've decided to find a service that can do the work not expensive and quick as possible. So later, I've found a service Aircon Servicing, Cleaning & Repairing Singapore | SoCool Pte Ltd that have troubleshooted my problem pretty quick. You know, sometimes you should relly on people...