elderly neighbor"s refridgerator would not defrost

I ordered the defrost timer and then read a couple of repair history stories. The timer was fairly easy to install. Then I advanced the small knob until I felt a "click". The covers were reinstalled inside the freezer. And the appliance is normal. Plug and Play. I learned that the timer is for the activation of a heater in or under the freezer"s aluminum fin assembly. Alot of folks don"t know that a refrigerator gets it"s supply of cold air from the freezing compartment. Everybody is happy. Thanks