I have a 1.5 year old Maytag MBF2556e, freezer on the bottom. About 3-4 months ago, I noticed that the fridge was kind of warm (in the 60s), so I called a local repairman, and he told me (i'm actually surprised he told me this instead of charging me to come out to tell me) that the freezer probably needed defrosted, that most likely someone left a door open, causing condensation on the coils and it froze. I did what he said and it seemed to work. However, two times since, this has happened again. I'm pretty sure the door is not being left open. I called the repairman back, and once again he gave me some advice. He said that it could be one of three things: the thermostat, the heater, or the circuit board. I priced out the parts and they aren't too expensive, but is there a way to narrow down which one it is, and are these parts that I can replace myself? And, any recommendations of where to buy the parts as inexpensive as possible? Thanks.

Scot