R134 retrofit on 88 Eldo. 273ci V-8

When computer warned me freon (R12) was low, I decided to retrofit to 134 as with my other vehicles. I took car to shop to check for leaks
(none) and evacuated the R12. I returned home to install R134.
Problem is, compressor wont engage to uptake the refrigerant/oil. It accepted one can, but no more, and this is probably just filling the volume of the voided lines. Checking with A/C gauges shows inadequate pressure on both high and low sides. Belt, fuse, and compressor are OK. I need to know if there is a circuit or switch, etc. Is this a Cadillac feature to require dealer service? Is there a computer code required? I notice there appear to be 2 accumulators. In short, what is the trick to get the compressor to run so as to permit recharge, pressure check, etc.
Any help or advice will be greatly appreciated.
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