I recently bought an ice cream truck with an older Bally cold plate freezer. It has a top mount condensing unit with a Copeland compressor 1/2hp. the freezer went to minus 2 after my first overnight charge now goes to 0 and loses a couple degrees per hour after that... it is a 3 bay freezer with a fourth bay fridge(Closest to the compressor) There is moisture that drips down from the fitting that is into the compressor(I think the pipe from the compressor into the freezer gets frost on it. There is rust that follows the path of the moisture. In the Fridge bay there is rust on the floor on the rear half of the compartment. There is no rust in the freezer bays but this unit is supposed to go to -20. The condensing unit overall looks old with rust the compressor seems to be resealed and is loud...makes a lot of noise at start up then quiets down. I believe it has R12 but no proof...

Questions: Any thoughts as to why it won't go to -20?
How long does it usually take for one of these freezers to charge to reach -20?

Should the compressor always be running? 10 hours straight? or is it supposed to shut off?(Mine runs all night...I suppose to fight to reach temp)

Any help with diagnosis and solution would be helpful.

Thanks for you help. let me know what other info would be helpful.