a/c blowing hot air on 1997 Ford Expedition

I was using my a/c fine, a few hours later, it was blowing very hot air. A/c is charged. What should I be looking for to repair it?
Help! Temps in the desert are above 100 degrees!!

Asked by for the 1997 Ford Expedition
When you operate the air conditioning switch on and off with the engine running, with the hood open get a friend to listen and see if you can hear the air conditioning compressor cycle on and off each time you press the ac button.If the air conditioning compressor doesn't engage you will have no AC.
The fuses in the AC circuit are fuse 24 (10 Amp), fuse 23 engine compartment (40 Amp main fuse) operates blower motor relay and blower motor circuit if blower motor works this fuse is OK. Fuse 5 (15 Amp) protects the heater blend doors (diverts air through various air ducts), fuse 23 (10 Amp) passenger compartment fuse box
One third of the cars in our shop today were in for air conditioning work. Summer is here!