Is there anyway to activate the pressure switch manually?
You would need to test (with a multimeter or continuity tester) if the switch was normally closed or normally open (when the unit is powered off).
If it is normally open, a small push button with short lengths of wire could be added across the switch solder joints.
If normally closed, a bit more work is required, but it is fairly easy if you have the right tools.
1.Why is the pressure switch in line with the bottle/jar inlet?
2.What happens if a bottle/jar is not connected and when the machine sucks air from the bag wouldn't it also be sucking thorough the bottle/jar inlet? It clearly doesn't but how does it achieve that?
1. To allow it to depressurize the container you connect it to. The *bag lid* must be closed during this procedure.
2. In my unit, the bottle/jar connector has a shutoff valve that is only opened by inserting the spigot of the bottle/jar attachment - a separate piece of equipment.