Clogged Orifice Tube
A fixed orifice tube contains a small brass tube of a fixed diameter encased in a plastic case. The case contains a debris catching filter at each end. It's located between the condenser and the evaporator core. It’s usually easy to locate, because many manufacturers crimp the line that holds the orifice, preventing it from traveling down the tube towards the evaporator core.
The orifice tube can become restricted and clogged with debris. A clogged orifice tube is typically caused by compressor failure. When this happens, little pieces of metal and aluminum shrapnel will be found in the tube's screen filter. If the filter’s filled with white or brownish debris, the desiccant bag in the accumulator has broken, sending desiccant throughout the system. This restriction will cause high high side system pressures. Restrictions result in frost forming around the restricted area.