I have a 93 Cadillac Deville that recently stopped cooling and the Service Air conditoning light has come on. It does not blow any thing but warm air. Does that mean that the system is void of any freon? If that is the case and there is no freon in the system can I convert to r134r coolant by using a conversion kit and charging the system with the new coolant? Could there be any coolant remaining and should I have it vacuumed as a precaution before using the kit? Any reccomendations?