Both the volume and strength of the ammonia mixture in propane-powered refrigerator cooling units are custom made according to formulas from the manufacturer. The concentration of ammonia and the volume of the entire amount of mixture are designed to give optimal performance from that cooling unit.

The mixture is "cooked" by letting pure anhydrous ammonia bubble through a column of aqueous-ammonia and chromate (a rust inhibitor–makes the misture look bright yellow) until the desired concentration of ammonia is reached. This ammonia concentration is measured in units called baumé (it’s a French unit of measure for specific gravity) using a hydrometer that floats in the column of liquid. As more ammonia is bubbled through, the density of the mixture decreases and this density change is measured by the hydrometer. When the correct baumé is reached, the mixture is now a refrigerant and is ready to inject into the cooling unit.

After injecting the refrigerant into the cooling unit, the head space is charged with pure hydrogen gas. The required hydrogen pressure varies, but it’s usually in the range of 250 to 300 psi.

Of course, none of this should be undertaken until the original leak has been located and welded shut. More information on repairing your cooling unit here.

Have fun!