This is a 5 years old side-by-side, model # GSS22IFREWW. The freezer door was left open all night and the unit iced up a couple of weeks ago and stopped cooling properly - things in the top of the freezer started thawing and the refrigerator section was clearly not cool enough. Turned it off for about 17 hours and lots of water ended up on the floor - taking the food out revealed ice on the back of the freezer compartment. Started it up after the 17 hour thaw-out and it worked well for a couple of weeks, but now it's frozen up again and not cooling well. The motherboard was replaced about a year ago under warranty. On this unit, is the defrost timer built in to the motherboard? Any suggestions on what, and how, I should check next?