Your problem could also boil down to a leak in the sealed system. I'm referring to the evaporator or condenser coil or connecting tubing. This system carries the Freon to and from the compressor. Many chest freezers have the evaporator coil built into the cabinet walls of the freezer itself making it next to impossible to find and repair a leak in the evaporator. Leaks in the condenser are quite rare but they do happen. They can be repaired if they can be accessed. Connecting tubing to all these components can also leak Freon. You'll want to check for leaks on all this tubing. If you've have several compressor change outs and find the system still doesn't work properly -- I'd be looking for a Freon leak. With all your compressor change outs you could be looking at the possibility of a sealed system that's contaminated. If this is the case it will need to be carefully cleaned and cleared of debris. It's a difficult process. Servicing the sealed system, working with Freon, the proper reclamation of Freon and...