The reason it is only 20 minutes is because it is turning on a heating coil, (provided that the coil and the power circuit is working), and the heat dissipates the ice much faster than shutting down the cooling system alone.
I have a Samsung RF261 french door refrigerator with bottom freezer. A few months ago the fan started making noise and I found out from the web that this was a common problem because of ice build-up. So I followed some instructions that I found on the web to manually defrost the refrigerator. Press Power Freeze and Fridge buttons simultaneously and then select the defrost option. When I did this the first time, I was pressing all sorts of buttons, but I finally got the refrigerator to defrost and the problem was resolved for some time. Now, the problem is back. So I tried the manual defrost option, but what I notice is that the defrost cycle only runs for around 20 minutes. After I press the Power Freeze and Fridge buttons simultaneously for around 8 seconds, the display panel goes off. Then when I press any button, the panel toggles between "FF", "OF", "rd", "fd". I am assuming that the "rd" option is the refrigerator defrost and this is what I am choosing. The refrigerator keeps beeping for around 20 minutes, and then starts operating normally. But this just seems like a very short defrost cycle.
Am I choosing the correct option to manually defrost the refrigerator?
How long should the manual defrost cycle last?