You don't have a timer on your refer. Find main board on back of refer. Find the 2 or 3 wire connector that is marked comp, line, and defrost. Unplug refer. Put a jumper wire from line to def. Plug refer back in. If your heater turns on replace main board. It also a good idea to replace the thermistor located on the evaporator. They're cheap and it will ensure trouble-free cooling until next time it breaks down.