No restrictions in the system that I know of. I flushed everything out last year. R134a wasn't cutting it, so I am exploring alternatives. I have R12 but before I go that route, I would want to replace the hoses to be sure there are no leaks. I would also have to flush out the PAG150 for mineral oil and that is a PITA. What I am testing with is not conventional freon so it has slightly different characteristics.