Air conditioner Gremlin

New here…hope this is the right place to ask this…

Have a 1992 Oldsmobile Custom Cruiser station Wagon…little over 92K miles. My problem is the air conditioning. Essentially, the only time the air conditioning stays on is when the car isn’t moving. It is an Electronic Climate Control system. What happens is when you start the car and turn on the A/C everything is fine. When you start to drive, the A/c shuts off completely until you come to a complete stop and have to push the button again which will turn it back on again. As long as you just sit there, it will run and get cold, but once you start moving again it shuts off. It doesn’t matter the speed you’re going or the rpm of the engine, it has varied between 10-30 mph when it shuts off. Shifting gears doesn’t make it go off either. It comes on when you start, shuts off when you move, starts again once at a complete stop and will keep running until you move. Don’t know if its a switch, low charge or what but when it is running when car is stopped it is cold air. I guess I should also mention that it is still running with the R-12 refrigerant. I want to retrofit it for the r-134a…just would like to know a possible cause…never have dealt with anythign like this before…