Isolation valve switch on the 737NG
 

Hi,

I have read that positioning the Bleed 1 or 2 or L or R Pack Switch to "off" would open the isolation valve when this valve is set to the "auto" position.
Therefore for engine start the L and R pack switches are set to "off" and the isolation valve switch is put to "auto". This opens the isolation valve for the air transfer from engine 1 and APU to engine 2 during start.

I found a youtube video explaining this at 00:52s

However in the top drawing at 00:52s of this video, the pack valve is clearly situated directly(!) before the pack.
If I switch e.g. the left pack valve switch to "off", with the isolation valve switch in auto, the air from the right engine should additionally feed the left pack as well.

But due to the position of the valve in the drawing this will not be possible since the pack valve is sitting directly before the left pack and thus blocks the air from getting into the cabin in the "off" position.

Is this just a mistake in the drawing or is it me not understanding the systems?

Correct.

If you switch the pack off, no air is moving through the pack, hence there is no air from that pack going to the cabin.

Thanks! I got it :)