the ac lines going to the rear headliner vents are both cold, but slightly warmish air is blowing out. since my truck is the 98, it doesnt have the separate ac/heat controls in the back, only the fan ****. It is driving me nuts; the ac in the front is cold, and the lines are cold heading to the headliner, but no cold air back there. what could be stopping the cold air from blowing out? evap coil?

 

could be a dirty evap coil if the lines are getting cold going up to it.