R-134a is the refrigerant used in all
USA cars these days. This is most likely what is used in the Eurozone as well. Unless your refrigeration unit is marked as using some earlier type, R-134a is what you should get for your unit. Make sure it is refrigerant only, no added
sealant or lubricant.
You will need the valve that punctures and closes off the pressure seal on the can and a short hose with an adapter to the connector on the low side of your compressor. I got the adapter at a
commercial air conditioning supplier.
In the absence of pressure gauges the procedure for my Frigoboat F35V is to have the compressor off long enough for the
refrigerator to be at room temperature. Then place the can upright so only gas (no liquid) will flow. Then remove the LOW pressure connection to the compressor, vent some refrigerant from the can to purge the lines and quickly connect the hose to the compressor. Open the the can valve and wait a short time (15 sec or so) for the pressure to be balanced. Close the valve, disconnect the hose and reconnect the compressor lines.
In the
USA, the refrigerant cans can be resealed by removing the valve assembly after each
charging.
This will give you a close to normal charge of refrigerant.
But... Sometimes air or moisture has entered the compressor/ evaporator system, you will need to draw a deep vacuum to remove contaminants. You might find an auto a/c repairman to do this if you don't want to spend the US$200 for a vacuum
pump and manifold. This also is a leak test because the gauges should show the vacuum holding for a good while after evacuation.