The orifice tube on a Ford truck is a hard debris filter for the air conditioning system. If a component in the system fails, the orifice tube prevents the debris from the failure from spreading throughout the system.
The orifice tube resides in the liquid line between the receiver/dryer and the evaporator. The liquid line brings refrigerant into the evaporator, the component that removes heat from the air in the passenger compartment.
The refrigerant flows through the AC system, outward from the AC compressor, through the manifold hose, condenser, receiver/dryer and evaporator before returning to the compressor.
When performing a full AC system inspection, after evacuating the system with a refrigerant service machine, remove the orifice tube and visually inspect it. If you note any signs of debris in the line, the AC compressor is most likely coming apart inside and requires replacement.
