A/C gremlins... need advice:)

[Nobody]

Hi, for years I am trying to fix my A/C problems with no luck. So maybe some you will have some hints. Joe?
Now it is new filled with no big leakage. Definitely there is some very small leakage as I have to re-fill it every two years but it cannot be found so easy (several times tried with color "coolant" to find weak points with no luck).
So symptoms are:
Compressor switches on and off "randomly" - it seems it works fine at temps around 20-25° but is not so willing to switch on on higher temps. It is strange that even with cold engine it will not start even on N, sometimes switches on on higher revs and during drive.
Revs sensitive - it seems it behaves like revs sensitive - on higher revs mostly working, on lower switching off more often, than switching on, off...
Temperature sensitive - seems while there are really hot days and engine is hot it hardly switches on and if yes, than after while switches off and again. I think there is some sensor which shuts A/C compressor off while engine is being overheated as engine radiator and A/C radiator are in front of each other.

I think it is not caused by A/C control unit as I have spare car and tried to switch them - works the same. It is probably not by any sensor - no error codes after diagnostic. On ECONO mode works fine blowing air according situation (sun, out temp...). Sometimes low revs of vent being on N and increasing with engine revs during drive (old car:-))

So I may assume the problem is at electric or at compressor itself. As I have spare one it is not problem to change current one to spare one but do not want to trial and error method, rather fix it:-)
Thanx for any idea.
Petr