The problem with a 134a conversions is that they often cause more leaks than they fix. 134a is a smaller molecule and can find it's way out through smaller leaks then 12. My advice is to try jumping the low pressure switch on the receiver dryer to see if the compressor operates. That will let you know if the compressor is ok and if the electrical portion of the system is ok. If the compressor comes on, then you are low on charge and have a leak. The most common leak is the condensor mounted in front of the radiator, it gets hit with road debris and stones all the time. The line under the r/f headlamp is also a common leak followed by the compressor. None of it is cheap to fix.
--
'86, '88 740 GLE; '88, 89 740 Turbo, '88 760 Ti (stolen), now '92 965