after reading a lot of q&a on this topic, I've decided that my circuit board is the problem for the following reasons, but feel a second opinion is a good idea.
Yesterday I noted a frosty spot on the back of the freezer and the frig too warm, over 40 degrees F. Freezer was at zero F. I removed the back panel in the freezer and found the evaporator coils partially frozen, over 1/2 ice logged, but less that 3/4. I defrosted using a hair drier and but the system back into operation. It seems to work better now, but not right. The frig has cooled down to 34 F, the freezer below zero, but it seems to be struggling to get there. I think the circuit board is bad as I have noted the freezer temp to be at -9 F (setting -4 F)and the frig at 42 F (setting 33 F) and the frig never seems to stop running, although the temps do cycle up and down.(??) The controls on this unit are electronic. Is there a spot I can check the board resistance, as on other units, to help determine for sure the board is bad? Also, coils are clean and all fans seem to be working. Thanks for your help

Thanks for your reply, I took the back of the freezer apart and checked the diffuser, what a chore, but it appears to be working properly. There was only a little ice in the evaporator coils, lots of frost. I removed the ice and put the shrouds back in place and reset the temps. I had turned them down to see if the compressor could generate very cold temps. Even though it was a lot of work, I'm beginning to think that maybe the door didn't close properly and the high humidity we were experiencing caused it to ice up. I'll wait another week and see if we have the problem again before buying any parts. Thanks for your help.