Auto Air Conditioning & Heater Repair: 2003 Ford Expedition AC, thermal expansion valve, orifice tube

Question
My ac blows cooler at highway speeds and warms up when I slow down. I was told the orifice tube may need to be replaced. I checked the temperature blend door and it is working. Where is the orifice tube located and could it be the problem.

Answer
  Your system is TXV type not orifice tube type.  The TXV (thermal expansion valve) is a variable way to control the refrigerant flow through the evaporator.  An orifice tube system on  Ford is typically part of the liquid line that goes to the evaporator.  The TXV is mounted on the evaporator inlet/outlet.  Not a common problem but it can happen.
 I would closely look at the condenser and the ability for it to radiate heat from the refrigerant.  The reason it works well on the highway is because thats when airflow is at its maximum.  Make sure it is not dented, plugged with debris and make sure your cooling fan is working properly.

Good luck..