Freezer, freezes?

We have a Kenmore Elite frost-free side by side refrigerator with ice maker. It's 2 years old but for the past 2 year+ we've been having problems with the freezer building up frost around the inside, and then the refrigerator doesn't get cold. I have to unplug everything, take the shelves out of the freezer and then blow-dry it sometimes twice a month, and then the refrigerator gets cold again.
I had Sears while under warranty come in twice they replace some thing and 3 months later the same thing happened, I had to call an so called expert to change something else first cost me $75.00 and the second time $150.00 and still have the same problems.
The seals around both the freezer and the fridge side are fine, so that can't be what's causing the problem. I've removed any dust buildup both under and on the back of the fridge.
I just wish where I could take it to sears and just dump it in front of their door.
thanks