Common issues with defrost timers are that they either get stuck in cooling cycles or stuck in defrost cycles, or they do not work at all.

• Stuck on defrost cycles: The compressor will not work and if there are defrost heaters they will be extremely hot unless there is a defrost sensor installed.
• Stuck on cooling cycles: The compressor will continue to work and will eventually cause ice to build up on the evaporator as there is no way the defrost cycle event will occur.
• Not working at all: This will prevent either the compressor or the defrost cycles to occur.

Common issues for a timer to fail are caused by either the actual timing unit being at fault or the contactor switches located inside the unit. These could be burnt out or melted.

Possible Solution

To test, you can locate the common wire on the timer and connect it to the Cooling Cycle circuit. If the compressor runs while the timer indicates that it is in a Cooling Cycle, there is a good chance the contactors are faulty.

The opposite is true where if you want to test the Defrost Elements during the Defrost Cycle, you can connect the common wire with the Defrost Cycle wiring.

Alternatively, you can use a spare timer to test if the cycles are working.