the fresh-air door does work and it does improve the performance.Also I overhauled the mono valve and, in economy mode the air is not being heated so i think that's OK as well.
Far as I'm concerned, the fresh air door can stay closed. The Silver Shadow I have is all recirculate if I understand the manual. It works fine and is a lot less complex system, but it would be since it was made in 1970. the good old days!
I know the condenser is a little small on the 420; I thought about a parallel-flow condenser which might help. Seems like there was a factory PF condenser on the later Diesel model which would fit perfectly, for only a lot of money.
I just wondered about the cycling; it looked so smooth and even that I figured it was evidence of a properly-functioning control. What about the pressure? About right? If the suction pressure were a little lower would the evaporator operate at a lower temp, therefore higher capacity? But then, how to get it lower: remove some charge, or? what is the limit for a converted system?
Best converted system I have seen is a 94 Suburban: ice cold and no problems since conversion about 5 years ago.