First let me tell you what I have done. Over the years I have repaired, maintained the a/c systems in my cars and in my home. So, I do know a little about how they work. I have a 1984SD 300 in excellent condition. I love the car and would like to keep it. Here in south central Florida it gets very hot so I need a good working a/c. Now let me tell you what I have done.
Using the fine article on Diesel Giant web site. I did everything exactly as on the web site . I took every thing apart, flushed the condenser, evaporator, and all the lines. Blew everything out several times. Installed a new R4 compressor, dryer and expansion valve. Drained the new compressor poured in 4 oz of synthetic oil and 4 oz in the dryer. I wanted a R12 valve but could only get an R34a. Vacuumed it out for an hour and ½ filled it with some R12 I had. Checked the vent temperature at 60 degrees blower on high. Put blower on low, vent temp went to 59 degrees. Engine rpm @ 2000. Ambient temp is 95 with high humidity. Air will not come out of the center vents unless I move the vent lever to the center of its range. This may be important I don’t know.
My pressures are low side varies from 35 down to 20, high side 210 to 240 due to the expansion valve working. Inside at the evaporator the temp at the input right above the expansion valve is 60 and the out put back to the valve is also 60 degrees??? The high side input to the valve is barely warm. At the condenser the input is 127 deg. And output is 98 deg. What is going on here? Looks like the evaporator is starved. When I blew air through it there was plenty of volume. How could this be? I checked the coolant hoses from the monovalve and they are cool so I don’t think it is a heater problem as the vent temp at start up is 60 degrees with a cold engine. The does compressor does not cycle either.
Because I don’t know where to go from here I am going to change out the climate control with one I have I know is good.
I don’t want to be like gpracer on the forum who sold his Mercedes because he had the same problem as I do. All help will be greatly appreciated.

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1984 300SD 175,000 Miles
1987 GSXR 1385cc
1985 GSXR Limited Edition 750cc
2005 Suzuki Burgman 650cc