Can't get cool

Have 1988 Town car with automatic temperature control A.C. system is fulley charged compressor cycle on and off can only get 60deg out of system last year was 38. It will run at 60deg for a time then will blow warm air.Removed ATC check vacuum was good cleand air hose adjustment on temperture control cable in its place.What else should I be looking at or fore? ALL HELP GREATLY APPRECIATED

What are the pressures? High and Low. That will tell you if ur low on Freon or if there is a blockage. Does the Electric Cooling Fan come on? Is the condenser and radiator clean of bugs and dirt? Is the car over heating?

Bryan