AC Intermitted and AC Blowing Through Defrost Vent

1500 Dodge Ram V6: I am having problems with my AC system. The system is intermitted, I can turn the system on and it will not blow. But while I am driving or running idle it has a mind of it's on to turn on. Once it is on, the AC blows through the defrost vent, when I change the settings it may or may not switch to the correct vents, mainly it blows through the defrost vent. I have changed the check valve near the fire wall on the passenger side. I'm in TEXAS and I need my AC.