I just added some 134a refrigerant to my dash cooling system.
After purchasing a hose with a gauge for installing the new freon, I just added freon until the gauge showed my system barely in the OK range. It took all of two recharge cans and could take a little more. It has been cooling just fine. Filling a 36 foot line on my DP is a bit different from an auto.
I could find no capacity or manufacturer info for my Over The Road system.
1995 38' CC Magna #5280
C8.3L 300hp Cummins, 31,000lbs