Refrigerator wouldn't stay cold

Bought it used. Worked fine for 32 days, past the warranty, then started getting too warm. Called a tech who didn't find anything. Checked here and saw 3 parts that might be at fault: refrig. temp control, freezer temp control, defrost timer. The time was most expensive so I started with refrig. temp control. Didn't help. Bought freezer temp control. Didn't help. Discovered that condenser fan motor was sticking. Replaced it but didn't solve problem. Finally bought defrost timer. That fixed it. Works fine now. Replacing parts was easy, requiring only simple tools.