I’ve frozen collection jackets (even with glycol) for a couple or three reasons. During recovery not injection.
Heat wasn’t on.
Valve on jacket was closed.
Quick connect wasn’t actually connected.
I guess I’ve also had an ETS actually freeze during injection. No glycol that time. Didn’t try that trick again till I had glycol in my jackets.
Once upon a time I ran HC-50 in the jackets on my PX-1 so I could switch between the heating and cooling loops at will. it worked, but I probably wouldn’t do it again.
I prefer the hot or vac / cold or vac setup @Graywolf gave us many moons ago