I have a Maytag ABB222ZDEB freezer-on-bottom fridge and I just experienced what i can now see is a pretty common problem of freezer cold and fridge too warm. I determined that this was caused by the return vents from the fridge compartment being blocked by snow. I cleared the vents and the fridge is cooling again. However when I removed the back panel of the freezer I noticed quite a lot of ice building up. So, obviously the defrost cycle is either too short or not occurring at all. Problem is I can't figure out how to tell the fridge to go into "defrost" mode so I can check if the heater is coming on. There is no defrost timer that I can find in this fridge, there is only the main control panel above the lights in the fridge compartment, and a "Thermistor kit", "Thermostat kit", and of course the heater itself. So how can I tell this fridge to go into defrost mode so I can check the heater?
Thanks!

The defrost terminator (i think that was it, little black round thing clipped onto the copper cooling coil at the back) was definitely surrounded in ice but it's clear now that I took a hair drier to the whole area. Maybe I'll see if that just works now. Thanks!

well everything was fine for about 2 months and then the fridge was warm again. I removed the back panel of the freezer and not surprisingly everything was covered with snow. Now that I have the service manual (thank you very much!) I was able to force a defrost cycle and that worked perfectly. So now I know that my heater element is working. Must be the timer then I suppose?

Since my last post I have not had this problem anymore. I never replaced anything. Check to make sure nothing is blocking the vents at the bottom rear of the fridge like milk bags or anything. If those vents are blocked the fridge will not cool properly and you will have freezer frost.