OK, I know, you lot must be getting sick of questions on this now but it would be nice to get it working again.

From what I see, the system works with a high pressure part and a low pressure part, the low pressure bit being able to be topped up with a kit.

The question I have is this, am I right in thinking the low pressure port is the one along the middle of the bulkhead with the thicker of the pipes and the high pressure port is the one on the thinner pipe on the left of the bulkhead? (Car is a 1998 DSE)

There is only one system with a high pressure and a low pressure side. The gas is compressed whih makes it hot, it is then cooled by the condensor, pressure is then dropped in the evaperator where the gas absorbs heat. A top up kit will only fit the correct connector as they are different sizes.