On a fridge there are generally no coolant lines running through the door but please check to see there are no lines connecting the door and the rest of the refrigerator. Check along the hinged side to make sure no lines jump from the body of the fridge to the door. A safe way to be certain is to check to see if the door can be mounted to open in eithe direction--if so there are definitely no refrigeration lines running to the door.

To test for coolant lines on a chest freezer freezer, start with a warm freezer then plug the unit in with the lid open. You should be able to see the lines form condensation on the inside of the freezer where there are lines running. Please still use caution when drilling.