Considered to be the heart of the air conditioning system, the compressor pumps and circulates the refrigerant through the system. Replacing the A/C compressor is typically one of the most expensive auto A/C system repairs. For that reason, extra care should be taken to assure that it never runs out of lubrication. Understand that typically, the compressor is the only moving part in the system and is the only reason that the A/C system includes oil. The compressor is also a component that splits two different sides of the system. The A/C compressor suction creates the low side of the A/C system while the discharge or compressed refrigerant creates the high side of the system.

The compressor suction, created on the downstroke of the piston, pulls low side vapor refrigerant from the evaporator. Through a series of reed valves, which are wafer thin valve plates used to control the flow of refrigerant in the compressor, the compressor then compresses that vapor refrigerant. In doing that, it changes the low pressure refrigerant vapor from the evaporator into high pressure and high temperature refrigerant vapor, pumping or discharging it to the condenser.

As noted, replacing the A/C compressor is one of the most costly auto A/C system repairs. That is because when replacing the compressor, it is important to assure that the entire system is clean and free of contamination, debris and moisture.

Understand that any moisture in the A/C system reacts with the refrigerant to create harmful acids. Those acids corrode the aluminum components, like the condenser and evaporator. When that occurs, the corrosion creates a contaminant that is circulated throughout the system. That contamination starts to plug up expansion valves, orifice tubes and any filters in the system. For that reason, it is critical to assure that whenever replacing the A/C compressor, the entire system is flushed.

In addition to flushing because of the corrosion, it is critical that receiver driers or accumulators are also replaced whenever a replacement compressor is required. The drier or accumulator is on the auto A/C system in order to trap and hold moisture. If corrosion is present in the A/C system, it is most likely the fault of the drier or accumulator being contaminated with excess moisture and not able to hold any more. Also understand that driers and accumulators include filters to trap and hold contamination. When the system becomes corroded, it should be considered that those filters are also contaminated.

With the A/C system flushed and a replacement receiver drier or accumulator installed, you must replace any lost refrigerant oil. Typically, when replacing the A/C compressor, you would drain the oil from the old compressor and add back that same amount plus one ounce to the new compressor. Use caution when adding oil and be sure you understand the amount of oil included in the replacement compressor. Every manufacturer uses different standards when they ship replacement compressors. In some cases, they include the entire system charge of oil. In other cases, they do not include any oil. It is critical that all oil in the replacement compressor is drained before installation. Once drained, replace the compressor oil according to the instruction above.

In addition to the replacement drier or accumulator, when replacing the A/C compressor you should seriously consider adding an liquid line filter. Typically referred to as an in line filter, these filters will trap and hold excess debris and contamination while still allowing refrigerant and oil to flow. When selecting a filter, remember that you want to provide extra filtration before the expansion valve or orifice tube. That will assure those components remain clean and continue to flow refrigerant and oil throughout the system. Do not install suction side compressor filters that are typically installed in the suction line of the compressor. They perform no function (other than making you think you have a filter installed) and in some cases, can actually cause your replacement A/C compressor to fail.

Some suction line filters are secured inside the suction line. They are only press fit into place. There are countless different sizes of screens that only vary in size by a few thousandths of an inch. In other words, they are easily mixed up or confused. Where the problem lies is that if the wrong screen is installed or even if the correct screen is installed incorrectly, the compressor suction will pull that screen into the compressor. When that happens, the compressor you just installed will suffer immediate catastrophic failure without any notice. Stay away from suction side in line filters, specially those that install inside the suction side line.

Once installed, the A/C system will require a deep vacuum for at least 1/2 hour or longer if possible and then be filled with the factory specified amount of refrigerant.