Såhär står det i servicemanualen.
http://www.kaelte-bast.de/dateien/pana/th/sm_cs-me7.10.12.14cb1p,cs-me10.14cd3p.pdfF91 Refrigeration cycle abnormality
When the compressor frequency is above 55 Hz and the current drops below the prescribed level continuously
for 7 minutes, operation stops, and it is restarted 3 minutes later.
When the compressor discharge temperature has exceeded the setting and the expansion valve has remained
fully open for 80 seconds, operation stops, and it is restarted 3 minutes later.
When the stopping described above has occurred on 4 occasions, operation stops, and the trouble display
appears.
<Diagnosis checkpoint>
1. Check the refrigerating cycle: Gas may be leaking (more than one-half of the volume of the gas has gone).
The diagnostic displays resulting from a gas leak generally change in the following sequence depending
on the extent of the gas leak: H99 → F97 → F91 → H16.
The range of this trouble (F91) is limited. (Compressor protection at the start of the season)