Yes, low charge will cause short cycling. What that means is the compressor is cycling out too soon and doesn't run long enough to work properly. There is a pressure switch on the low pressure side of the system that will cut power to the compressor coil at a certain setpoint, usually around 20PSI. There are 2 reasons for this-one is to protect the compressor from running when there is not enough refrigerant/oil being pulled into it, the other is to keep the evaporator from freezing up. If there has been nothing done to the system in 20 years, it's very likely low. No a/c system keeps its charge forever. Eventually, seals and o-rings get old and start to leak. If it's a small leak, you may be able to get a shop to top it off, or go to a parts store and get a can of 134a and a low side hookup. This would allow you to top it off yourself. Hope this helps.

Scott

Yeah, that makes sense, thanks for explanation. I think you helped me a lot. I will update you on this case when I resolve it if you are interested.
And yeah, does it make any difference if i change out refridgerant or add how much is missing because i heard some shops are changing refridgerant?

Have a good day!

Update on my case
Diagnostics showed i had 400 grams of 134a instead of 850, and 12ml of oil. System is now filled with 850 grams of refrigerant and 10ml of oil (dont know why if there was 12 but macanic said its okay, that most cars are okay with 10.) Cooling is now significantly more efficient at higher fan power settings, but still my compressor is disengaging while driving. I find that annoying and im worried about clutch wear. Since its working continously on idle and lets say 1500 rpm my guess is that compressor is ,,overpowered" for that system because all liquid refrigerant may not be able to evaporate before exting evaporator if compressor is running at higher rpm. It bothers me quite a lot because im driving on straight road for half an hour at exactly 50mph, engine about 2250 rpm in fifth gear and my compressor is disengaging every 25 sec, wich has no sense to me at all since that is relatively low rpm. It just gets worse when driving on highway...