A/C blowing cool not cold...

I have a '73 Dart Swinger, 318 2bbl all stock, stock A/C RV2 compressor. I bought the car two years ago and never really use the A/C. The other day it was hot and turned it on. Compressor kicked on and got cool air, definitely not cold, but cooler than on vent. I looked through the records that I got with when purchased and the system was flushed and filled in 2007 with R-12 and was noted in working order on shop receipt. Also noted in the sight glass some bubbles. I have an R-12 can and was wondering if all it may need is a charge. Also if I charge it on the schraeder valve on the head of the compressor itself.... any help would be greatly appreciated, Thank You in advance....:thumleft: