From time to time, refrigeration and air conditioning systems suffer failures that result in contamination. The most common such failure is a compressor burnout. During such an event, the refrigeration system becomes contaminated with large quantities of disintegrating particulate, sludge, acids, carbon residues, and possibly moisture. All of these contaminants must be removed before the system is returned to duty.

In earlier years, these systems were flushed with the popular CFC-based solvent R-11. Non-flammable, plastic-safe, and with a very low boiling point, this material was favored because it was safe to use, cleaned efficiently, and was easily removed from the system.

Unfortunately, R-11 was a major ozone depleter and was gradually phased out of production. Since that time, many companies have attempted to market alternative flushing agents based on terpene, hydrocarbon cleaners, acid flushes, and oil additives.

Among products on the market today that have been found to be effective is Rx11-flush™. (For more information, see sidebar.)

Whichever product you choose, it is necessary to flush the contaminated system.


When flushing a system:

  • Use only the appropriate refrigerant, proper recovery equipment, component parts, tools and lubricants.
  • Do not inject the solvent into the compressor itself. In fact, the compressor should be removed or bypassed. Only the supporting refrigeration system should be flushed.
  • Large systems or systems with unusual configurations that could trap the solvent should be disassembled and flushed section by section.
  • A single canister will flush a 5- to 7-ton system. However, the exact amount of flush required will vary by the internal design of the system, the nature of the system failure, the degree of contamination in the system, and the temperatures at which the failure occurred.
  • If the system to be flushed includes large components, such as a receiver, it is recommended to use a visual inspection. If these components appear to be contaminated, and they are small enough to be flushed, then do so. If they are too large to economically flush, then the use of additional solvent (such as degreasing solvent) is advised.


    The following equipment is required for each flushing operation:
  • New canisters of flushing solvent. For a typically soiled system, you will need one canister for every 5-7 tons of cooling capacity.
  • An injection tool and standard refrigerant charging hose to inject the solvent into the system. The charging hose and injection tool should be dedicated and retained for future flushing.
  • A small, resealable, waste container that will hold the solvent after it is flushed through the system. Ideally the solvent in the container must be visible, so it can be inspected during the flushing process. This enables a technician to determine when the solvent begins to run clean, indicating that the system has been thoroughly purged.
  • A tank of clean compressed nitrogen, regulated to 120-150 psig. This tank should be equipped with a dispensing hose and will be used to purge the solvent from the system.
  • A vacuum pump with the appropriate hoses and clamps.
  • Clean wipes or swabs to remove any residual oils or liquids that may drip or be spilled while purging the system.
  • Safety equipment; never flush a system without eye protection and rubber gloves. Convoluted piping in certain systems can cause momentary spikes in the solvent flow during the flushing process, resulting in erratic purges, which can splash into eyes and onto skin.


    1. Confirm you have all the required components for the service as well as for the flushing operation prior to beginning.

    2. If the system is still operational, remove the existing refrigerant and lubricant using the appropriate methods and recovery equipment.

    3. Review the configuration of the system. On larger systems, disassemble sections of the system so those individual portions can be cleaned section by section.

    4. De-energize all of the electrical leads and ensure they are safely positioned. Remove the following components: Disconnect the old compressor and remove it from the system. Remove filter-drier cores. (If it is easier or more cost-effective, install a bypass loop around the filter-drier accumulators, etc.) On heat pumps, remove check valves and four-way reversing valves. Again, configure and install bypass loops.

    5. Connect a waste container to a discharge port to capture the contaminated flushing solvent. As this solvent exits the system, it will contain oils, condensed water, acids, particulate, and possibly other mechanical residues. While not normally hazardous, such residues need to be captured for proper disposal.

    6. Connect your charging hose onto the system to be flushed. Make sure openings upstream — except the discharge port — are closed. Connect the injection tool to the canister. It is a good idea to restrict the drain or discharge point, so that the flushing solvent is prohibited from passing through so quickly. This will improve the cleaning process.

    7. When ready to inject the flush, connect the canister to the charging hose. Open valve on tool; the flush will start entering the system.

    8. Discharging the flush should take approximately 10 minutes, depending upon temperature. Before the tank is empty, some small quantity of solvent should begin to flow into the discharge container. Also, the canister has been designed to empty itself completely only when it is standing in an upright position. Do not attempt to flush the system with a canister inverted or on its side.

    9. Using the compressed nitrogen tank, connect the tank to the system and blast it into the system behind the flush solvent. The nitrogen will push the solvent through the entire system, agitating it and “scrubbing” the inside of the system. Eventually, all of the solvent will flow into the receiving container on the other side of the system. In this step, it is recommended that the nitrogen be used at a low pressure at first, with the pressure being allowed to increase gradually.

    10. Observe the solvent being captured by the receiving container. If it is running clean and clear, the system has been successfully flushed. If the solvent is murky or still contains particulate, flush again.

    11. Make your repairs. Remove any bypass loops you installed. Tie in the expansion devices. Replace the filter-drier cores. Secure the system.

    12. Evacuate the system to a low micron pressure range with the vacuum pump and leak-check the system. This will evacuate any residual liquid solvent from the system. As the internal pressure drops, the solvent will boil into vapor and be removed from the system. Time for pulling the vacuum should be approximately 15 minutes for a 5-ton system.

    13. As a final step, recharge the system with refrigerant and lubricants as recommended by the compressor or equipment manufacturer and the system instructions. Reconnect electrical and electronic connections. Test the operation of the system. Wipe down the system, leaving the work area neat and clean.


    The waste solvent will contain used oils and other organic contamination. Pour the contaminated solvent into a waste oil drum for proper disposal. If the solvent needs to be transported, care should be taken to ensure the container is properly sealed to prevent spillage.

    If a second canister is required to fully purge a larger system, you do not need to disconnect the injection tool from the refrigeration system. Simply close the valve on injection tool and remove it from the first flush canister. Replace it with a new canister to continue flushing. Canisters may be recycled.

    Do not smoke or use an open flame around these materials.

    Lawler is director of Product Management for Nu-Calgon. For more information, contact the company at 2008 Altom Court, St. Louis, MO 63146; 314-469-7000; 800-554-5499.

    One Possible Flushing Agent

    Formulated by the same chemists who produced the original R-11, Rx11-flush was created to offer the benefits of R-11 without the environmental concerns.

    It is considered ozone-safe, non-toxic, nonflammable, and compatible with most materials in a refrigeration system. The cleaner itself is packaged in a pressurized container, designed to purge a moderately contaminated 5- to 7-ton air conditioning or refrigeration system.

    According to the manufacturer, it dries quickly, has a low boiling point, has no aroma, and will not attack components.

    Its low boiling point enhances complete evaporation. It can be used for new system cleaning or retrofits. The solvent is approved as part of the United States Environmental Protection Agency’s (EPA’s) Significant New Alternatives Program (SNAP).

    Publication date: 12/04/2000