The system has a low pressure cut-off switch. Does just what you see if the charge is too low, in order to avoid compressor damage.

I am fussing with my 1997 965 wifemobile which has begun to not cool enough. We are having high humidity (up to 90%) and without sufficient cooling the atmosphere is vey uncomfortable.

If your loss of cooling occurred in a very short period of time, you may have a large leak which can also allow the PAG refrigeration oil to escape.

A good a/c shop can use a dye to determine leak location and give you a repair quote. Just adding R134a is a DIY job. You may need a more complex fix.

Look for my posts on a similar subject recently, good answers that I got will help you.

Good Luck,

Bob

:>)