Hi Herb -
I also have a 91 LS400 with 245,000 miles and about 4 years ago, I made the decision to convert from R12 to R134a and it's really cold. It started out with a bad compressor. I replaced the compressor with a brand new nippondenso. From there, I changed all the rubber hoses followed by the expansion valve (which involves removing the evaporator under the dash). I then flushed every ac line, condensor and evaporator to remove all the old r12 oil followed by removing and replacing every oring in the system. Finally, add the new R134a oil, evacuate and recharge with r134a. The total for (most parts) from Lexus was about $800 + about $200 in flush, r134a and misc. The bottom line is to stick with R12 unless you are willing to do the conversion correctly.
Hope this helps with your decision.
Wednesday, April 29th, 2009 AT 11:36 PM