freezer needs defrosting

Update. I left the fridge on for 3 weeks, empty. Found a little frost, but nothing serious. I then loaded the fridge & freezer and have been out for 7 days. I found about 1/8 of ice on the back and a little on the top of the freezer. So, back to defrosting. I have done the seal test and had a repair guy look at it while doing other work. He said everything looks good. the only thing i can think of is the door being open too long as mentioned earlier. the other thing i tried on this trip was to open and close the fridge door slowly, thinking opening it fast would suck out cold air leaving warm air to come in. As stated above, the results were having to defrost the freezer after 7 days. FYI, we traveled from the NW to AZ, in case humidity is a problem as mentioned earlier. I welcome any other ideas as this is driving me nuts.