Thanks for the info guys. This has already been hacked together and getting it working was most important. Just putting off the replacement for a bit.
You could always completely fill up the receiver and make it act like a critically charged system again, or probably better yet, just remove the receiver.
One of the machines is a Virtis Ultra LE 25, has daul compressors with receivers and caps.
Filling the reciever will make for interesting start up. Remove reciever and install cap tube drier or some other access for highside. In the 80's I serviced an ice bank bulk tank with captubes and recievers. The recievers were due to length of evap. tubes. Thus large volume of refrigerant required to flood
Of course, anyone doing Ultra Low temp long enough knows that some of the normal rules get ignored.
Most of the units where I've found them receivers installed with cap tubes had 1-2 year old compressors with bad valves. I'm surprised those little guys lasted as long as they did. ;)
The shelf compressor only cools the shelf, it has two caps. One cap is for cooling, one is for when the recipe calls for no cooling. The condenser compressor cools the condenser of course, unless the switch is off. If the shelf is on and the condenser switch is off the condenser compressor still runs and supports the shelf cooling.