Auto A/C systems require filters in order to trap contamination and debris. Understand that it takes less than one tenth of a teaspoon of debris to cause serious problems in any A/C system. That debris is a result of moisture contamination in the system.

When moisture and refrigerants mix, there is a chemical reaction that causes harmful acids to form. Those acids corrode the A/C systems aluminum components. That corrosion travels throughout the system and will restrict the flow of refrigerant and oil if it is not filtered.

The biggest problem is that conventional filters in the A/C system are easily plugged. Filters like the inlet screens of orifice tubes or small cone shaped inlet screens sometimes located at the inlet of thermostatic expansion valves are easily overwhelmed with even the smallest amount of contamination. When those filters become plugged, the flow or both refrigerant and oil are restricted. That can cause catastrophic compressor failures.

Understand that the cold refrigerant that cools you also cools the compressor. Also understand that all of the lubrication that the compressor requires travels as a mist in the refrigerant. When refrigerant and oil flow is restricted, you are operating the A/C compressor without cooling or lubrication. It will not function that way for long.

Filters or in line filters are typically added to the high pressure side of the system. The most effective location for any filter for the A/C system is in the liquid line between the condenser and the expansion valve. Filtering refrigerant at that point will help to assure that the expansion valve does not become plugged and that it will continue to allow refrigerant and oil to flow.

Alternative type filters that fit into the compressor suction provide absolutely no protection and can even cause compressor failures. Understand that in order for any contamination to get to a suction side filter, it would have to travel up the walls of the evaporator and through the accumulator before reaching the filter. The reason that the contamination particles will not reach those suction line filters is because of the physics of what is happening in the A/C system. In the evaporator, refrigerant is actually boiling. When any liquid boils, it is actually being filters as solids and contamination in the liquid to not travel through to the vapor.

In addition to that, even if the contamination got through the evaporator, the only exit from the accumulator is a vapor outlet. By design, the accumulator forces all refrigerant to become vapor before it can be pulled by the compressor suction. It is absolutely impossible for solid contamination to flow through the evaporator and accumulator. The suction side filters are really useless.

In addition to that, most of the suction filters are designed to be press fit into the suction line of the compressor. If the press fit fails, the suction screens have been known to be pulled directly into the rear suction port of the compressor causing immediate catastrophic failure without any warning.

To assure proper and effective filtration of contaminants from the refrigerant in the A/C system, you should always install liquid line filters that install between the condenser and the expansion valve.