What are you getting for a center outlet temp? What are the pressures now? Is the compressor cycling? Does the low pressure line get frosty? R134a retro fits do not perform as well as R12 systems due to the compressor piston displacement and the size of the evaporator. Was the new compressor designed for R134a or R12? How much of an oil charge got put in and how much of the old oil got removed. Excessive oil can decrease overall efficiency of a converted system.

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Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.