Sanden Compressor as an alternative
Another alternative for the original airco compressor, is the Sanden 5H14, formerly called 508. The Sanden compressor is a modern type compressor with smoother action, compared to the York. The most important factor is that the compressor chosen can function with the "not normal" anti clockwise rotation, and this is fairly unusual.
By Lars Frykholm:
There are certainly other kinds that will do, as long as you check that they can work in the inverted rotation of the SM system. Officially the Sanden doesn't, but in practice it does, but for other makes it's best to check.
Mounting is easy, just get two bits of right-angle alu profile and shape them for the standard mounting. The very simple way of tightening by pushing sideways works fine.
A suitable oil for converting to modern gas is Castrol's Retro oil.
Change drier filter and mount a double action cut-out switch on it. On one car I've recently fitted a more modern parallel-flow condenser, said to be more efficient (Tripac Superflo Multifit 07-1403A). It may be a good idea to fit an extra fan directly on the condenser, pushing. The expansion valve in the evaporator housing often needs changing.
The point where modern cars differ a lot is the size of evaporator but there I have as yet no solution. Maybe somebody else?
You also need to check that the vacuum switch for recirculation works, and spread the knowledge that with the red-to-blue switch in the far right position you get recirculated air.