Filter Issues
The freon inside your refrigerator uses a filter to remove any unwanted particles. Because the refrigerant line is a closed line, it is unusual for the freon to carry many contaminants, but sometimes this occurs and the filter becomes full. An old filter may eventually create a clog in the lines if it captures too many particles. Having the filter changed can usually fix this issue.
Contaminants and Valves
Contaminants in the freon lines can also cause problems for other components. The refrigerant system depends on a series of valves that control where the refrigerant flows and what component it is currently locked in during the cycle. Contaminants in the freon can cause these valves to grow old, stick and create clogs even if the filter is not yet clogged itself. Valves can be cleaned if you are willing to take apart your system, but replacing them is typically a better option.
Compressor Problems
The compressor is the pump that forces the freon into a high-pressure state, allowing it to collect heat at the same time. If the compressor pump begins to fail, it can start blocking the freon, running too slowly and developing other problems that cause a build-up of refrigerant at the wrong time. In this case, replacing the compressor can solve the problem. Compressor noises or long cooling cycles are an indication of this issue.
Leaks and Other Issues
If you believe you have a refrigerant clog, you may want to have your system tested before you jump to any assumptions. A refrigerant leak can be very difficult to notice, and low pressure in the freon lines can create many of the same symptoms as a clog. If you have recently filled your lines, there may also be too much freon present to create proper flow.