Weird HVAC problem

[Previamanvan]

So to make this short, I started having a problem where the fan wouldn't kick on at all unless I banged on the fan housing. The compressor would kick on no problem but not the fan. So I replaced the blower motor itself since it wouldn't work on any speed. Then when I turned it on it only worked on high. So I replaced the resistor and all was well for about a week now. Then today it didn't turn on the fan again... So I played a bit and once I changed the orientation (ie changing from face to defrost) and magically the fan turned back on. So I'm at a loss. What could cause my fan not to work unless I change the orientation? This is beyond my intermediate expertise with this van. Any insight is appreciated. Thank you in advance!

[Jsp]

Check electrical connections to the defrost switch. Just follow the wires and check for problems.
Usually a bad ground can cause problems.. Fuses are okay though?

[TheMAN]

make sure the blower switch is good too... the terminals tend to melt due to poor design