deluxe old big side by sides often had the 3 heaters you describe.

the shaft turning is good but the timer must advance thru its cycle of
off and on incoordination with a sensor. if that frost sensor is not
satisfied you may be in a continuous defrost mode.

pinpoint your make and model and look at your answers

http://fixitnow.com/wp/category/refrigerator-repair/

which will refer you for parts and model illustrations at
http://www.repairclinic.com/0047_4.asp