1994 Chrysler New Yorker freon like out

I am disabled. I bought my son a clean car with low miles. 94 new yorker with 42k. the air doesn't work. we bought a kit and put 2 cans of freon in it. it worked fine but the next morning it had all escaped. we don't have a lot of money and I would like to help him repair it as cheaply as possible. Is there an o-ring or connection that is problematic with these cars that is more than likely the leaky area? Please give your advice on the freon leak. Thank you!