Engine control system? what does it mean?

It sounds like your AC compressor is going bad. Most vehicles also turn on the AC when in defrost mode, since the AC also acts as a dehumidifier.

You might try unplugging the Heater/AC blower motor and see if the sound goes away.
https://www.youtube.com/watch?v=WAXvlcUqkfo
https://www.youtube.com/watch?v=mBh1k6Fjy6k
https://www.youtube.com/watch?v=zgxLGo8kpi8

https://www.youtube.com/watch?v=mcKJs8OcjUE

https://www.youtube.com/watch?v=RIwmOyT7AAo

could be you a/c compressor, you may need to have the pressure checked

Vacuum supply starts on the drivers side of the engine. There is a vacuum line going into the brake vacuum assist from the manifold. branching off of that line is a double line that snakes under the intake manifold, behind the valve cover, along side the valve cover on the passenger side headed to the front of the engine. Then it curves to the right side of the engine. One set of hoses from this line goes to a valve control (red and green i think). The other line goes to the vacuum storage ball, it should be black. The vacuum circuit continues out of the ball in another black line that snakes into the firewall. It goes under the heater core black box and disappears under it. Now go into the passenger compartment and drop the glovebox. look to the back right you will see a black and a white vacuum line coming out of the firewall. The black line is your vacuum supply from the engine. It goes up to a little rubber manifold. disconnect the lines coming from the dash switch and check for vacuum on the manifold where the black line is going in. The white line controls the cabin air intake under the glovebox and the thermostat shutoff under the hood. It should only have vacuum when the switch is in a certian position, AC probly. The other three lines coming off the rubber manifold snake behind the dash vent door assemble and come out near the gas peddle. The red one controls the dash vent. apply vacuum to the red hose and see if the vents go to the center dash position/AC. The yellow and blue? ones control the floor vent control near the gas peddle. yellow gives you half floor and half defrost. blue gives you all floor. you can use a small vacuum line to connect the black vacuum supply to each individual line on the manifold and check the function of each vacuum control assembly individually. I hope this helps. On my truck each control unit works fine when i apply vacuum to them individually but when I hook the dash switch up to the rubber manifold it goes to defrost. I tried changing the dash switch and the lines running from the switch to the rubber manifold and the vacuum ball under the hood, nothing works. I suspect I may have leak i just haven't found yet. next step is to get a vacuum gage and start checking the amount of vacuum i am getting at each vacuum line. I'm sure it is supposed to be getting a specific amount of vacuum and will not work if the vacuum drops below a certian level due to a leak in a line somewhere? God bless.

It's located behind the right side of the dash.

With a bad or worn fuel pump you would first experience lack of fuel at higher speeds.
If the engine is shutting off with the extra power demand of the air and heat then that indicates an electrical problem. Battery or alternator.

Have your radio code before you pull it out with the right radio tool. This pull would involve removing this parts.

1. Glove compartment
2. Driver side panel
3. Center top dash board
4. Defrost switch carrier
5. Radio unit
6. Center lower half of dash

So I'd suggest go to your local public library and look for your car manual. It would be either Chiltons or Clymers manual, it's not as precise a Bentley VW Official factory repair manual. Yes it really involves taking all those parts out just to get to the rotary switch.

the problem is with the blend door it controls the blend of hot and cold air. there is a small electrical motor that can go bad or they can hang up
you will probally have to take some covers off to find out whats going on

You can save a LOT of money by fixing it yourself.

All that is wrong with the knob are broken wires from the knob's PC board to the main PC board on the AC control.

All you have to do is remove the AC main control, take it apart, and resolder the broken wires from the PC board with the knob on it, to the main AC pc board. There are 3 wires, any number could be broken.

If you take it apart and solder the broken wires, this WILL fix your issue. Just make sure you put the wires back exactly where they go.

A FIXYA rating (4 blue diamonds) would be most appreciated for my assistance.

Is it in the center of the dash or in the right corner? The one on the right is for the ABS. The one in the center is a general message. Using the read function on the signal stalk there will be an explanation of the light.