It illegal to open up a A/C system with out a licence. Commercia, home, or auto/diesel. Even if it isnt working there is probally trace amounts of the refrgerant left in it. And if it is 30 y/o it is consivable it contains R-12. Not really sure what they used to use in the older home units. There are severl types of refrigerant depends on applications(home, commercail, auto)