TRIAC controlled fan voltage issue
Assuming there is a neutral to ground connection somewhere between your supply transformer and your building ...







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. Switched neutral.

It sounds as though the triac controller is in the neutral line.


  when I take voltage readings at the fan terminal box I get 120V readings from Line/Ground 


That's the VM1 reading.


  and 120V from Neutral/Ground 


That's VM3. The live feed is coming through the lamp filament.


  but zero volts from Line/Neutral.


That's VM2. The lamp is off and there is no voltage drop across it.