A VolvoS70 requires a precise amount of freon. You need to buy the freon gauge for the vehicle. Then open the hood and look for two identical caps, they are ususally blue to green in color. This is the area where you add the freon. Please make sure to use the freon gauge to not overfill the A/C.
The best option for adding freon to any vehicle is taking it to a certified service, as freon is highly regulated and the process does have a degree of danger
You need to go to an Air Conditioner mechanic to deal with the Freon. The old Freon needs to be removed & disposed of in a certain manner required by law.