Where's heater control valve located on my 1995 E150 with 351w engine?

There is no "heater control valve". Your heat is controled by a blend door. Vehicle Application: 1995 E-350 Econoline 5.8 Customer Concern: The heater will intermittently start blowing cold. When this happens, the heater hoses still feel hot and the temperature gauge in the dash is always steady. Tests/Procedures: 1. With the heater blowing hot, disconnect the electrical connector from the blend door actuator behind the Right Hand (RH) side of the dash and recheck operation. 2. If the temperature still changes on its own to cold, remove the blend door actuator and check for a broken temperature blend door. Replace the broken blend door as needed and recheck operation.