Not sure if I need a part!

Well a month ago the air stopped going to the fridge from the bottom freezer, i looked in the bottom freezer and a plastic bag was against the back vents, i took it out and unplugged 12 hours to melt’. worked for a month and packed it pretty full of food, now it iced up again. Unplugged for second time. Did not pack too tight this time. If it does this again what do you think the part is that i need?
Thanks ahead of time, John.

John,

There are three parts in the defrost system. They are: the defrost timer, defrost heater and defrost thermostat. One of them is bad. You have to perform the troubleshooting as described in one of our previous threads: http://forum.appliancepartspros.com/refrigerator-freezer-repair/4221-freezer-fine-refrigerator-too-warm.html

Here are the breakdown diagrams and Replacement parts for MAYTAG MBB1954GEW REF - BOTTOM MOUNTS | AppliancePartsPros.com

Gene.