When I turn on my fan switch on my 96 e350 the fan will not work. I was able to slam the passenger side door to get it to work but not any more. Any clue what it could be?

 

I'd have that passenger door checked----surely its at fault here for no heater blower right?

There are several parts associated with the heater blower operation so you'll have to diagnose this in order to effect a repair. As we don't know your level of mechanical skill this is most difficult.

The blower switch, resistor network, fuse/relay and of course the blower motor itself can be the problem here; any or all of these can and do cause this condition.

A simple and fairly easy test is running a 10 gauge wire directly from the positive battery terminal to the blower motor terminal. If it works then you have a problem upstream in the control circuit.