Typically, filter-driers are rated per AHRI standards which require no more than a 1 psi pressure drop at its maximum flow capacity. That is the basis for how they are selected and so it should give you an idea of what is “normal”…ie, 1 psi or less. If the pressure drop exceeds that, it may be time to consider replacing it.
If you pick up a new replacement filter-drier and check the recommended maximum load or tons listed on the back of the box, you may see one rating for air conditioning and another, lower rating for commercial refrigeration.
One additional rating you don’t see on the box is a higher capacity rating for OEM equipment manufacturers…which explains why filter-driers on new equipment are usually quite small in comparison to what you would install in the field.
One reason for this may be because a factory installed filter drier is considered to be installed and a brand-new and therefore clean system. Field replacements on the other hand are installed on systems that have been in service for a long time and also have been opened to conditions less than ideal.
Another reason, of course, is cost.
…and the idea that a refrigeration system should have a cleaner filter-drier than an air conditioning system is debatable in my book. 😉