I have changed a fitting my (87 cougar) a/c that has been converted over to R134A a few years ago but the guts in the other connection are leaking/bubbling. Are the guts the same as a tire valve stem or are they different?

I put 2 12oz cans and stopped because the gauge that came in the kit showed that I was in the correct level. Today on the way home from work, the a/c didn't work very well. It blew cold and then changed to warm air and back and forth. I think that I need to add more. I didn't use a vacuum pump to evacuate the system because I don't have access to one.

 

They are in essence the same but of different size than a tire valve.