 Then the system doesn't work, and it hydraulic locks the compressor and blows it up, and now you're looking at $500 to $1,000 repair. Oh, great. Because you tried to save a few dollars by putting a $10 can of something in it. So there's really no way to top off an air conditioning system without removing all the refrigerant, weighing what you took out, and then put back in exactly what it needs. And if that's 13 ounces, you put 13 ounces in.