Maytag refrigerator that the refer top half has gone warm, freezer still works

From the sound of it I would looking at the evaporator fan in the freezer. This is what circulates air and actually cools the refrigerator as well as the freezer

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Most likely cam kit / door close kit at bottom hinge needs replacing

As far as my knowledge I know that this freezer is using insulation in the door for putting out warm air and keeping cool air inside. Your refigrators insulator has gone bad. You yourself cannot assess it without proper device and you will also require a new insulator to replace the bad one. My suggestion to you is to kindly let me know how old your refigrator is and how far you can go with repairing it.

Sounds like the compressor is gone, or the coolant has leaked out. If you can hear the compressor kicking on then the odds are the coolant is out.

bad evaporator fan and or a defrost problem

You can get the step by step instructions (lots of pictures of each step) to repair this exact problem at:
www.AnyoneCanFixIt.com (specifically at http://www.anyonecanfixit.com/household.htm scroll down towards the bottom to look for Warm Refrigerator and Cold Freezer repair). It will save you a lot of money to do it yourself!

You can turn the thermostat off for now to let the ice thaw out, if a door was left open there might not be anything wrong, but if it freezes up again sounds like you might have a bad defrost heater or defrost limit. Hope this helps

The adaptive derost control has gone bad a very common issue. It will work a couple of weeks before its back to its frosting over. It just plugs in but to get to it you must remove the controls at top of frigde section in the back right corner held in by two scewrs.

Most likely the heater is bad. It is located under the evaporator inside the freezer rear wall . Look for a long glass tube about half inch in diameter with a long coil of wire inside. That is the heater . It can be unplugged easily.

Check that the freezer circulating fan is running. The frige section may have dampers or vents (lets the freezer air cool the refer section) that are open too much. Usually the bottom area in the frige has a control lever to meter how much cold air gets to that section (lots for meat, little for fruits, etc.). Check the owners manual for operation of those vent dampers.