A defrost termination switch can work in several different ways. When your freezer goes into defrost the clock is set to a particular duration. If the defrost termination switch senses that the coil is free and clear of ice it will send a signal to the defrost clock to go out of defrost and turn the compressor back on. On some defrost controls the switch will not allow the fans to come on until the evaporator coil has reached a certain temperature. You would not want the fans to come on immediately after defrost or you would be blowing hot air from the defrost heaters onto to your food product.

Ref	Part Number	Description	Leads	Mount
1	12766	Defrost Termination	Red	Clip
1	12767	Defrost Termination	Yellow	Clip
2	13198	Fan Delay	Red	Flange
2	13197	Fan Delay	White	Flange

3	12455	Thermostat - Cooler
3	12769	Thermostat - Freezer
4	28994	Thermostat - Constant Cut-In
5	33085	Thermostat Protection Relay