Since it is AC there are no polarity issues. The wires internal to the heater are all black and it doesn't matter which one is attached to which leg of the 240V supply.
The wires providing power to the heaters shown in the pictures are black and white. To be compliant with current codes the white wire should be taped to show that it isn't used as a neutral wire (red or black tape).
I didn't fully understand where exactly you were measuring the voltage. If you measured from the single wirenut on the right side to either of the thermal protection switch contacts on the left side then you did correctly measure the voltage across the heating element (I think that is what you meant, I'm just not sure). -- Got some spare cpu cycles ? Join Team Helix or Team Starfire!
I saw that when i measured the voltage that there was no voltage if the wires were not connected but then when i would connect one heather than the voltage of the other wires going to the second heater would be at 238v and this is vice versa.