1.9 SDi Random RPM surge while idling with AC on. Could it be the AC Air Pressure Sensor (G65 Error)? Done extensive service

Hello,

I have a problem with my Fabia Combi 2003 1.9 SDi that is bothering me for a long time. I've spent much money on service but still haven't fixed the issue.

Only, and I say ONLY, when I turn my AC "On" I have random engine RPM spikes which (I presume) correspond to a cycling AC Compressor.
I went to a mechanic who told me to go and see an AC Specialist. AC specialist took down and inspected my compressor, said that it is okay, changed compressor's clutch (said it's slipping), put fresh PAG oil in it, regassed the system and sent me on way. AC still didn't blow cold and I still had random RPM spikes while idling with my AC on. I've noticed that the faster I drive the better my AC works. I presumed that the condenser fan might be faulty.

After some time I went again to another AC Specialist who showed me that my AC condenser fan isn't working. I've replaced the fan, told him to look at the level of refrigerant in the system (didn't need more refrigerant) and after the service AC started blowing colder. Not freezing cold (5-6-7 degrees Celsius as it should), but reasonably colder. Then I decided to clean the AC system with a foam cleaner and change the cabin filter. I did that couple of days ago, and I think that the AC blows even colder but I didn't have the chance to test it properly because now the weather is overcast with rain so the temperatures aren't that high. Will see results the first time the temperature goes over 33-34 degrees Celsius. This weekend I plan to use another can of foam cleaner to try to clean the AC evaporator through the condensation drain hoping that it will have some effect on cooling (I presume it was never cleaned).

After servicing all of these parts I'm still left with random RPM fluctuations when my AC is on. I've ordered VCDS diagnostics cable and I'm currently waiting for it to arrive and then I'll try to scan and see if there are any error codes. I'm totally guessing, but could it be that the AC Pressure Switch (G65 Error Code) is the problem? Maybe it's false readings cause the AC compressor cycling, or could it be the alternator? My headlights work, power steering is sometimes heavy (power steering fluid level is as it should be; also I think that the Fabia is slightly nitpicky about the quality of tires), but the battery is charging normally.

If anybody had similar problems and solved them or has some idea what it might be - be free to write.

Many thanks.
Boslo