where is the freon refill port by the compressor or at the right top end on 1996 Buick Century

I tried to fill ac with freon but it would not take it the port by compressor is to small. which is the lower port to fill. there are only two. but which one is it.

Asked by for the 1996 Buick Century
The refrigerant in your car's system is R134a not freon (R12), the service port connections are larger on the 134a cars you may have the high and low pressure ports all ready found if not, Autozone have some popular workshop manuals for free on line once you register (for free) on their website
and get an online repair manual subscription.
Is the low pressure port the one on the metallic bar in the middle against the Firewall with the black Cap? Or is that the High pressure one? If not where is the low pressure port? Auto Zone's Repair manual doesn't specify where the low pressure port is on the vehicle and it's not well marked. It's also not in the owners manual.