how to charge the a.c. on my 2002 Ford expedition

before adding refrigerant after locating suction port, be sure that the condensing coil located in front of the radiator is clean so it can dissipate the heat efficiently, also check and replace your cabin air filter, a dirty cabin air filter restrict the flow of air across the evaporator coil, now you could proceed to charging the system, if there is no refrigerant present when you connect you refrigerant gauges, then you might want to locate the source of the leak and correct it. Good luck.

Some moron decided to put the high side port in plain view and the low side (service port) that you need to service the system on the accumulator (the cylinder looking thing) on the passenger side firewall under a wire bundle and bracket. Good luck and have patience, you will prevail.