[jshafer13]

the freezer is working fine, but the fridg. side is not cooling. I inspected the freezer side & found that from the middle of the back wall to the bottom of the freezer is covered with ice. I cleaned the ice off cover the air return in the lower part of the freezer, but there is still a lot of ice build up in the vent holes. what would cause the ice. could this happen if the door was not shut all the way overnight?:

[woodchuck]

The open door would certainly let in a lot of moist air to freeze on the evaporator coils, but your defrost system should have melted it in a days time.
check defrost timer, defrost heater, defrost thermostat here...Refrigerator Repair Guide: How To Fix a Refrigerator - ACME HOW TO.com

In most of the new units they now have the adaptive defrost control instead of the timer. It senses when to defrost based on how many times and for how long the door is opened. It's more energy efficient but there does seem to be lots of problems with the board.
With your model number We could tell which you have

[kayakcrzy]

Yes it could happen if the door was left open over night. It could also be what Mr. Woodchuck said, about a defrost problem. If yoiu have a meter, I can walk you through the diagnosis. I can be reached at my website at ApplianceEducator.com Tom