found a closed thread dealing slightly with my problem, but anyone know the fix?

96 k3500

Air blows cold and runs fine all day. until you place the fan motor on hi. 15 min on high and the system quits. looks to be icing over. refrigerant pressure is good. Bad dryer?

Try replacing the on off cycle switch on the accumulator

You may want to check this site out--I've found it helpful in the past

http://www.autoacforum.com/