Vendo 6CV Doesn't Get Cold Enough - Low R12?

[chuggybear]

Hey everyone,

I was hoping someone could help me out with my Vendo 6CV.  My 6CV will cool down to around 43 degrees, and the capillary tube will freeze over.  The compressor will continue to run and never stop, but the machine won't get any colder.  Eventually, the capillary tube will turn into a solid block of ice.  The picture shown is about 45 - 60 minutes after turning it on.  I have checked all the door and cabinet gaskets and have added weatherstripping to stop any air leaks. 

I am thinking it may be low on R12?  How do I go about adding R12 to the machine? 

I see that someone added a Schrader valve to this machine as pictured.  Can I just buy an old bottle of R12, a charging hose, and hook it up?  Or do I need to make sure it is at a certain pressure? 
I don't have an ID tag on the machine that states how much refrigerant should be in the machine. 

Any help would be greatly appreciated!

[MoonDawg]

       Seems low on charge. Try topping it off with this, https://www.ebay.com/itm/FREEZE-12-can-R-12-REPLACEMENT-R12-Automotive-Refrigerant-12-oz-Johnsens-w-Hose/183793720700?epid=623314529&hash=item2acaf59d7c:g:fVUAAOSwXoJcyHGg , it may have developed a slow leak.

[johnieG]

Without a gauge-set he’s flying blind.