Replace Volvo VNL truck expansion valve. 

Symptoms: air at the back of the cabin is much cooler than at the front. Freezing pipes. 

Take the air filter and evaporator housing off while draining freon. You don't need to drain coolant.

unscrew 1 bolt holing front and 2 bolts holding back plate of the expansion valve  

Disconnect both freon pipes around the valve apart and pry the white rubber gasket in front of the expansion valve apart to create space for the valve to come out. 

pry the old valve out and put new one.