1990 lumina a/c system

Need a little help. I've got a 1990 chevy lumina with a 3.1. My problem is I'm not getting power to the a/c compressor. I've jumped the low pressure switch, checked the freon and all fuses and relays. there are 3 relays in a row 2 for the fans and one for the a/c. they are all the same so I've tried swapping them to see if it was the relay and still not getting power to the compressor. I'm getting power to the relay but somthing is telling the relay to not switch and power the compressor. Heres what I tried, I jumped the relay and the low pressure switch and that gives me power to the compressor. But if I take the jumper out of the relay it goes back to no power to the compressor. If anyone has any ideas I thankyou.

Try getting the system recharged. This will require a shop that has R12 refrigerant available. Also get a power probe & power to the compressor side to be certain.

Don't really know what I did, but it works. I jumped the low pressure switch and jumped across the relay to power the compressure again. put a can of freon on it and took all the jumpers off and it works. But that is the same thing I did yesterday. Oh and it was converted to the 134a several years ago. Thank for your help.

Could still be faulty relay. Keep tabs on it. Cool on the retrofit.

I just acquired my second 1990 lumina - this one is a euro 3.1 model tho and not the 2.5 model - my a/c also does not work - how can I tell if it is modified to R134a or still R12? - thanks