I'm perfectly satisfied with my 450SL that was converted to 134a from R12 6 years ago. Since that car uses a compressor with it's own crankcase oil converting oil only required pouring out the compressor and filling back up with 134 compatible oil (no flush needed). I've only needed to add about a can of 134a so far.
I repeat myself by saying that I live in a dry and rarely over 90F climate; This is not Texas. I know this would not be acceptable by many of us americans who crave what I would consider extreme cooling at home, work and in the car. This is none of my business but the point is I'm staying with 134a and I have no interest in changing the condensor.
This whole flushing thing has me concerned and a bit confused. I guess I will belly up and order the FJC flush kit for $36.05 and a quart of FJC flush solvent for $13.57. I expect to make a mess both inside and outside of the car. The expansion valve will be removed so even with buckets and rags I'll probably have a mess. I will have 8 hoses disconnected (2 @ compressor, 2 @ R/D and 4 @ at the exp. valve). Should I blow flush into each of the 8 hoses or should I just focus on flushing the condensor and evaporator. Will follow up by blowing lots of air through the system.
As for evacuation I was happy to find the Robinair venturi style one for $39.98. It's the one the previous poster (Rick) suggested I look at. BTW, all prices are from The Tool Warehouse. The spec says 29.7" Hg of vacuum. If standard atmospheric pressure is 29.92 I would have an absolute pressure of .22"Hg which converted in millionth of a meter is 5,600microns of Hg. (Did I calculate that right?). I guess most of you are telling me that that is not enough. Funny enough both places you mentioned, e.g. ackits.com sells this style vacuum pump and believes in them.
So my final sticking point is the pump. I will not buy a $200 one so I'm left with building my own (I wonder how many microns the old fridge pump is capable of) or using the Robinair venturi type. After all if I flush first and remove most the oil I would hope that I wouldn't be so loaded up with moisture in the old oil.
Thanks for all your kind words of encouragement and advise.