1998 Ford Explorer A/C wont blow cold

When the system is stuck on "defrost" mode, it is usually because your heater box uses vacuum motors to run the mode doors, and the vacuum supply hose is broken or disconnected. You'll see that hose shown on the vacuum hose routing diagram on the emissions sticker under the hood. Those systems are spring-loaded to default to the defrost position for safety. Your feet might freeze, but the windshield will be clear.

You'll have to describe all the steps you performed to charge the system with refrigerant. Did you just add or did you start with the system completely empty? How did you know how much to put in, and how did you measure it? Is the compressor running?