I went to find the schematic for your unit to find out what type of sensor is in it. Your manual says it has a temperature warning alert. This is what I found.
.A. Whenever "PCB Control Panel" button\'s pushed, the buzzer rings.
B. After 2 minutes power\'s on, the buzzer rings 3 times.
C. Time of Buzzer: Forced Defrost Mode (3 times), Short Circuit Test (1 time)
D. When door opens, the buzzer rings every 1 minute for 5 minutes.
Be patient here now. Hopefully we will cure this. Allow me to say first that if this were MY fridge I would rope it like a calf, tie it to my truck, and gas it!
Okay, so with further reading it appears this fancy gizmo is supposed to warn of temperature changes due to low freon, door being open and temp drop and so on so basically it could be caused by something you are unaware of or it could be errors.
To make this answer short I am going to post the link to the manual.http://www.fridge-manual.com/manuals/daewoo/Daewoo_RF-420.pdf
I graduated with an associates degree in electronics engineering this past summer and I cringed when I saw your manual so I will try to simplify what you see in that manual and say, unscrew the cap off the top hinge and unplug what you see. That will not harm your fridge and should make it shut up. Page 21 in the link.
Now in case your fridge light has been wired with that buzzer, which is probable since your device was made overseas you may leave it plugged in and check that the door switch isn\'t sticky. Put a flathead screwdriver to it and gently pry it upwards and it should pop out. Once you have it out push it in and out. It should spring freely. It IS possible whoever assembled it never put it in its slot snugly so the door is not touching it as it should. Prying it out and putting it back in may solve this. If the switch does not bounce freely when pushed it should be replaced. The switch can be unplugged to replace it if necessary.
My heart goes out to you. The manual is tough enough for the average non mechanical engineer but is lacking in basic English. Good luck.