is that the one with the yellow words MAX 6Nm the low-pressure port? I brought a can of 134a and a charging hose kit but found that the blue color socket did not fit. do I need an adaptor for that or i've just brought the wrong kit? how can I make sure the socket fit? is there a name or size of the refilling kit hose socket please? Thank you.

 

The low side port is on the larger pipe. That pipe if working normally should be cold (~35-40 degrees) with the compressor on. (pressure is close to the freon temp if you ever get a gauge on). You can't add freon to the high side with the compressor on - the pressure is too high.

It is a closed system and leaks are rare - Why do you want to put some freon in? The freon is put in by weight, and with r134 too much does the same thing as too little - poor cooling performance.
You also have a variable displacement compressor. A valve controls the angle of the swash plate changing the displacement. (and the pressures) First used (on Volvos) with the 2007-2015 6 cylinder engines - that valve goes bad and can present symptoms similar to low freon. (not cold when you want it to be) Google volvo variable displacement valve.

Ac service procedures have changed. Back with r 12 - if the system was not cooling, people would guess the system was low, add some freon and many times if would work better. With variable displacement and r134 - guessing usually does not turn out the results you are looking for.

 

thank you so much for the reply. It fact it has happened twice before. 2 years ago the AC was not cold and the garage helped me to add freon and it lasted 1 yr. Leak was not identified at that moment. The problem happened again 1 year ago and another refill also helped until now. So I just dont bother to find the cause and hope it will work another year from if i can refill it by myself to save some money. is there any advise about the hose kit that i should buy? any specific size or name of the adaptor?