You can add Freon, but please note with your boat year - it's probably R-22. Not R134a used in automobiles. If you are not an AC expert, I would call someone. Was it working fine before your pump lost prime? If you can access the unit, grab a hold of the thin line and fat line entering and exiting the compressor. The fatter line is the suction line and it should be cooler. The thin line is the high pressure line and it should be rather warm . . so be careful.
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2010 Vista 338 Volvo Penta
2005 Yamaha Wave Runner FX HO
2005 SeaRay 280 SunDancer
2001 SeaRay 245 Weekender