When a freezer leaks oil, it can come from one of several places. Freezers use oil in their compressors, where it circulates to regulate the compressor's temperature. Oil is also used for lubrication on freezer fan blades. If you notice an oil puddle near your freezer shortly after installing it or after it has been serviced, it may be from excessive lubrication and not a problem with any part of the freezer's refrigeration mechanism.
Oil that leaks from a compressor can come from a crack anywhere in the system. This includes the pump, the compressor housing or the supply lines that oil circulates through as it moves in and out of the compressor. A faulty pump or pressure control switch can cause the pressure to rise too high, resulting in a ruptured line. Likewise, an obstruction can force pressure to build up until oil is forced out of the system.
Other than noticing a pool of oil on the ground near your freezer, you can identify an oil leak using several methods. When a freezer's compressor loses oil pressure due to a leak, it may sound different than it normally does when it runs. A reduction in cooling may also occur if the problem is severe enough. Whatever the reason, you should be able to feel oil on the outside of the housing of the compressor or on the pump behind the freezer.
The location of the oil leak determines whether your freezer is a candidate for repair or you need an entire new compressor assembly. Each component that has oil flowing through it is essential to the freezer's operation, which means that any time you notice oil, you should consult a repair professional or attempt to diagnose the problem yourself as quickly as possible. A new compressor, gasket or oil pump can have your freezer running again before its contents thaw completely.