Based on the age of your travel trailer the roof Air Conditioner was originally filled with R-12 Freon just like what was used in car air conditioners of that time. The bad news is that R-12 Freon is no longer manufactured due to environmental concerns. R-12 Freon is now scarce and expensive to purchase; it is sometimes sold for $20 to $30 per can. In order to purchase R-12 Freon you need to be EPA certified unless you can prove that you are buying it for resale.
The good news is that there are now more environmentally friendly refrigerants available that are 100% compatible with R-12 Freon. Freeze-12 Refrigerant is an R-12 Freon replacement.
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