Frigidaire defrost timer issue

I found a forum topic that addressed my first issue, top freezer being cold but the bottom refrigerator warm. The freezer would completely frost over the back panel where the vents are. One of the first things it discussed was the defrost timer, so being the least expensive part I started with that. When I replaced the defrost timer the light comes on but now the compressor and the freezer fan will not come on. Just to see if I perhaps got a defective part I put the old timer back on and it still will not come on. Any suggestions on what to check next?