Do you know? When a refrigeration system is running the temperature of the cold room will gradually drop. The air volume in the room will also drop along with the temperature that will lead to the air pressure in the room to diminish. When the cold room is not equipped with a pressure ventilator, the higher air pressure outside of the room will push the panel body of the room inward resulting into the body of the cold room to be caved-in.
This kind of setting will make the door of the cold room, extremely hard to open because of the higher atmospheric pressure pushing in the lower air pressure inside the room. The greater the difference of air pressure inside and outside the room, the harder it is from the door to be opened.
There is also another setting where the situation is that the pressure inside the room is higher than the air pressure outside the room. This situation may occur in the process of defrost (especially, if the door has been opened when the temperature of the room is already low). When defrosting the room, the air volume inside th cold room will expand. Expanding air will push the body of the cold storage outward and damaging it making the panels convex.
When the this occurs, closing the door will be problematic. When closing the door some outside air will be push inside resulting the inside air pressure to increase even further. This situation will make it extremely hard to close the cold room door because of the outward push of air pressure for inside the room.