a/c makes hissing noise, doesnt blow cold

[Grdenko]

a couple days earlier my a/c worked fine, then it wasnt cold at all anymore and there was a hissing noise coming from the center vent.

the blower works and so does the heater.

could the hissing be a vacuum leak? how would a vacuum leak in the a/c affect its performance?
could this just mean im out of refridgerant?

thanks