I am modifying a existing piping system that has a header supported by 5 spring cans. I have predefined the existing spring cans in CAESAR II. The piping is configured in such a way that when the piping gets hot, the header inlet will grow down and the springs should compress. When I look at the spring table, the vertical movement shows movements of about -0.9 inches for all the cans, which makes sense. What doesn't make sense to me is that the table is telling me that the 2 cans nearest to the header inlet have a negative theoretical installed load and it says "in spring redesign option and could not find a spring in the manufacturers table that contained the design operating loads."

How is it possible that I can have negative vertical movement (compression in the spring) but have a negative theoretical installed load? What could I be doing wrong?

It appears that you entered a spring rate but not a "theoretical" cold load so the program attempts to reset your existing spring. My guess is that some of your hanger locations do not support (enough) deadweight in the first place.
You can investigate by running a weight analysis with rigid Y restraints in place of your springs. What loads do you get?

You are correct. I entered a spring rate but not a theoretical cold load.

The redesign mode will only use the existing spring rate if it can carry the "new" hot and cold loads. Certainly a negative installed load is outside the recommended range.
Can you send this model to techsupport@coade.com?