AC Expansion valve
On Series I it is located where the AC pipes go through the bulkhead (at least for a LHD car, I have no idea on RHD). The bulkhead bridge is an oval metal part surrounded by rubber, with two pipes leaving it. It is bolted onto a similar part on the inside of the cabin which is a part of the heat exchanger, literally through the expansion valve assembly. What you do is (of course once that the remaining gas has been evacuated) to unscrew the two nuts that hold the oval part on the engine side of the bulkhead. Then the oval part with the pipes can be removed carefully, as it plugs into the expansion valve assembly. The pipes themselves are slightly conical and have O-ring seals, as do the pipes that go from the expansion valve into the cabin. Therefore be careful when doing this as the valve may end up on the part you are removing, it's only held in place by the pipes, and the bolts go through holes in it straight from the cabin part to the oval bulkhead part that you are taking off. You cannot fit it wrong because the pipes are of different diameters: it only can be fitted one way for the pipes to plug into it.