Volvo S60 Aircon issue

[HarryS]

Good day, I drive a 2011 Volvo S60 D3 geartronic with 166 000km on the clock. I have started to notice the following with regards to the aircon,
• Subtle whine when aircon is on and I pull away or increase speed while driving
• The aircon takes forever to actually start to blow cold air (but even so it’s not as cold as it usually did a year ago)
• I took the car to have the refrigerant filled and was told it is fine and not necessary?
• The aircon pipes in the engine bay gets adequately cold
• I can hear the aircon click / Tick when I put the aircon on and off
We get very hot weather here and often drive on the freeway for 60km without the aircon blowing cold air and then other days after +-10km the aircon will start to blow cooler air, but not cold. I have noticed that the aircon comes on earlier and blows cooler when the weather outside is cooler (early morning).
Does anyone know what the problem can be, and can I fix it myself?