My Maytag refrigerator is working fine on top as a freezer, but not cooling on the bottom. I have already removed dust from the fan and the coils.

No cooling at all or insufficient cooling?
What is the temp. and where is temp. control set?

You may have an air restriction due to frost buildup (defrost failure), or the freezer fan is not running due to bad motor or bad switch. You have to use a meter to check it out.
Manuals: https://dl.dropboxusercontent.com/u/8010163/Maytag%20Refrigerators.zip
https://dl.dropboxusercontent.com/u/8010163/How%20to%20use%20Test%20Equipment%20Service%20Manu al.pdf