I recently bought a whirlpool refrigerator. It was working OK until I realized that the defrost cycle lasts to long. It lasts longer than 40 minutes. Can anyone say what's the problem?

Can't say wats wrong with your whirlpool refrigerator but can I give you a tip mine takes time too what I do is get my hairdrier hang it over the door of freezer pointing inside and leave it for a few minutes on warm .I put towels in the bottom to soak up the water .Works a treat for me he he