Read carefully the directions on the kits and be absolutely sure what type of freon is used in the kit. Your Mondial should be using R-12 (again, confirm with your owner's manual) and this substance is hard-to-get (as it is a hazardous product - eats the ozone layer in the atmosphere). The current type used is R-134a and cars can be converted to use it, but its expensive.
If you're not confident in DIY, bring the car to a specialist without hesitation. They maybe able to re-charge using the old-type (R-12), it depends on your location (some States still allow the use of the old-type)...