Which pipe to use to top-up refrigerant in a freezer?
The filler hose for the small cans only fits on the low pressure side.

The high pressure side should have a different fitting. This is how cars are anyway. So it is impossible to connect the refill can to the high side with the refill kit you buy at the auto store.

The small cans don't have enough pressure to overfill the system. So you can't overfill it. You could put the can in a bucket of warm water whole filling that will help get all of the refrigerant out of it.

Make sure it is running while you are filling it.

Good luck!