Fridge/Freezer would not cool to proper temp

Unplugged powercord. Removed the racks in the freezer. Removed the back panel. Noticed ice was completly covering the cooling coils. Defrosted the cooling coils. Removed the thermostat. Removed the screws holding the Defrost Heaters. Removed Defrost Heaters and installed new ones. Clipped on the new Thermostat. Replaced back cover. Put the racks back in. Plug the powercord back in. I purchased Freezer/Fridge thermostats to keep an eye on actuall temps.