CAA actually states that the York will handle R134 just fine. I expected them to try to sell me a Sanden conversion. I did buy the higher efficiency condenser which apparently is needed because of the R134 characteristics. I want an original appearance on my Mach 1 and I'm going through my underdash unit right now. My compressor was new about ten years ago and had R12 in it with no leaks. I'm draining it and changing to ester oil. We'll see.
I did search the board and there seems to be no consensus on this issue. There are a multitude of opinions about "higher head pressures", less efficiency of R134, and ester oil not being tolerant of ANY moisture in the system. York compressors were used on many imported cars in the 70s also, so the Porsche and Mercedes guys debate this too.
You can essentially keep the complete York setup including the compressor mount which will be the base for the Sanden after an adapter is added to support the newer comp. The dogleg is eliminated as that is a York mount-not needed. Also not needed is the tubular compressor brace that mounts on the intake and the York. The drier should no doubt be replaced and the condenser checked. Believe that R12 will cool better, but a good AC person can make the 134 cool the unit well. To be honest don't think the Sanden will be that much better cooling wise(all things being equal) but the vibration and noticeable drag will be eliminated. The Sanden will still use some power but again, not noticeable. This is why the dogleg and tubular mount will not be nec.
Did this install in a 65 cv and it is still a good cooling unit, after 4 years untouched.
Another benefit to those installing the original setup with the Sanden:If you car is PS equipped and uses the later Ford PS pump, it is NOT nec to change over to the slanted fill neck.
Air conditioning compressors have capacity rated by the displacement per one revolution of the compressor shaft. The York AC compressor was typically a model 210 which means it displaced 10 cubic inches per each revolution. When Sanden started manufacturing AC compressors for R134a refrigerant the capacity displacement units switched to metric measure.
For example a Sanden r134a unit SD7H15 displaces 154.9 cubic centimeters per each revolution. 154.9 equates to about 9.5 cubic inches. So this unit has slightly less capacity than the York. The last 2 digits in a Sanden compressor unit name (ie 15) is the cubic centimeter displacment divided by 10 and rounded to the nearest whole number.
Now the Sanden is an axial or wobble plate compressor and it will draw less horsepower and run at higher rpm than the York. If you notice the York compressor pulley is larger than the crankshaft pulley (so it would turn slower than the engine speed). It did not like high rpm. The axial/wobble plate comressors can take higher rpm so it has a smaller pulley. The higher operating speed of the Sanden makes up for its slightly lower capacity.
One switch is replace the serial flow R12 condenser with a multiflow or parallel flow condenser designed for R134a. R134a refrigerant has lower heat capacity per mass unit of refrigerant. To compensate you need a condenser with higher exchange rate to keep compressor discharge pressure from getting too high. Also make sure you have a 5 or 6 bladed radiator fan and fan shroud installed to increase air flow across the condenser at engine idle.
I converted my 1966 model to R134a with a multiflow condenser in 1998. I installed a rebuilt York compressor. Interior cooling has been adequate. The only problem I have encountered is that I cannot prevent the compressor shaft seal from leaking. In the spring of 2007 I replaced the York compressor with a newly built unit. These are still available from Climate Control Industries and look exactly like the York compressor from the 1960's. Even with a new unit the compressor shaft seal leaks. I want to keep the original look so the shaft seal leak is frustrating. The Sanden unit most definitely is a better design and will not leak.