Co2 rack

Started a co2 rack a few weeks ago. Sub critical 134A top cycle RDM controller. Here is the problem. The company that is programming the RDM is having a hard time fine tuning the sporlan steppers on the cascade evaps. Granted this is a learning process. The medium temp is liquid and low temp dx. The problem is top cycle starts to loose control and the electronic valves open too fast flood condenser floodback occurs starts to pinch down the valves superheat goes up co2 cannot condense vessel pressure rises etc I notice things happen very quick with co2 ex; loading cases systems coming out of defrost etc. I know the valves are oversized on the evap condensers. The guys doing the programming have been working on this for weeks. It's still not right and grand opening is soon. I'm getting bummed out

The Sporlan Steper motors are usually controlled by a PID loop(proportional, integral, and derivative) . Setting up a PID loop is more an art than a science and needs to be turned for every application.
I suggest you read up on PID controls.

Remember that refrigeration is a slow process (in computer terms), therefore use small numbers.

Also for starters set I = 0, and focus on getting a stable system (not necessarily the correct temp but just a stable system).

Welcome in the wonderful world of carbon dioxide refrigeration.

Decosta, I understand pid. The dance between the top and bottom cycle is a tricky one and is dependent upon the superheat remaining low and tight on your heat exchngers. First time seeing CO2 in a refer system. We have it working well now.