As you can see in figure 54b, only one of the power lines is connected directly to the loads (compressor, fans, and defrost heater). The other power line runs through the timer terminals before it reaches the loads to energize them. The timer motor, operating on a twenty-four-volt power supply, opens and closes contacts at regular predetermined intervals, causing the loads to become energized or de-energized (taking the unit to the defrost or run cycle). The frequencies and lengths of these intervals are regulated on the timer dial. There are two sets of contacts in the timer: (1) The normally closed contacts (terminals 1 and 2) and (2) the normally open contacts (terminals 3 and 4). When the normally open contacts are closed, the defrost heater becomes energized (only for a short time). The normally closed contacts energize the compressor(s) and the condenser fan(s). Terminal 1 connects power to the compressor(s) and the condenser fan(s). Terminal 4 connects power to the defrost heater. Twenty-four-volt power connected to terminals 5 and 6 energizes the timer motor. When normally closed contacts open, the normally open contacts close simultaneously and vice versa.
