Well folks, thanks a lot for your tips :-)

Guess I'll have to start saving up some money...
Paid $100 just for the conversion, and I can hardly start thinking of the costs for discovering the leak...

It is obviously a small leak. The system was tested with vacuum before being refilled, and showed no sign of a leak during the 3 hours of vacuuming.
The system has been operational approximately 1 month before quitting on me. Guess it'll be both hard to find and costly...

Two final questions though: Since my fan doesn't run at the "slow speed mode", there couldn't possibly be any connection with this and the lack of refrigerant?

And secondly, where do I look to make my fan operate at low speed again? And when is it supposed to run at low speed? All the time when the A/C is enabled?

Thanks a lot for your help!

Anders Eklo - Norway.