I just purchased a pretty nice, older ford E-350 superduty van. It has rear AC/Heater. The front heater works great, but the rear heater does not blow hot air, just cold. There's no place to adjust the temperature on the rear heater (it runs off the front controls).

The Haynes manual doesn't go into the rear heater too much, so I was looking for some direction. Does anyone have any suggestions on where to start my diagnosis?

Thanks for your help, Ian