Using Qwik System Flush by Mainstream Engineering to clean out a system.

“Do a job right the first time or don’t do it at all.” There is no better adage for flushing lineset systems. Flushing linesets is a preventive measure taken against possible contamination after R-22 to R-410A conversions and acid burnouts. Replacing linesets is, of course, the preferred method of preventing side effects of residual contamination, but at times a full replacement may not be practical or affordable, such as when linesets are under concrete or recessed in walls. Therefore, technicians may have no choice but to clean the linesets.

Given the phaseout of R-22, R-22-to-R-410A conversions represent the bulk of flushing projects today. Not every technician may know the proper techniques. Proper flushing techniques are also needed to flush and clean linesets following a system burnout.


The following 12 tips, if followed properly, create a foolproof lineset flushing sequence:

1. Wear safety gear.All flushing agents have some degree of toxicity. Service technicians must wear gloves, safety glasses, and any other safety gear to minimize exposure.

2. Purge with nitrogen first.Purging loose debris first with nitrogen allows the flushing agent to attack contaminants that adhere to the inner walls of the linesets. A good nitrogen regulator should enable the technician to achieve the recommended 120 psi. Oscillating the purge may also enable more contaminant to be dislodged.

3. Have enough flushing agent available.Starting and stopping the flushing process because of a shortage of flushing agent will probably require more flushing agent in the long run than the amount originally required by the job.

A good rule of thumb is one 2-pound canister of flush for a 7- to 10-ton refrigeration system. Extremely contaminated lines may need more than 2 pounds of flush. Since most flushing agent brands are sold in either 1- or 2-pound canisters (with the latter a better price value), it’s more economical to flush a 5-ton system with one-half of a 2-pound canister.

Most flushing agent brands require an access valve, which is an easy item to forget at the wholesaler, especially for first-time users.

4. Remove obstacles.Remove any expansion valves, filter driers and other obstacles.

5. Cut up linesets of 50 feet or longer.A flushing agent works best and has more flushing pressure in shorter runs, or segment lengths. Therefore, lengths of 50, 75, or 100 feet or longer should be cut, flushed in sections, then soldered back together.

6. Restrict the opening.Crimping the opposite end of the lineset will induce more pressure within the lineset and help dislodge additional contaminants.

7. Collect the debris.Use a bucket at the receiving end to catch used flush. All flushing agents have some degree of toxicity, requiring the products to be disposed of according to the Material Safety Data Sheet (MSDS).

Biodegradable flushes require the same disposal methods as used refrigeration oil. However, nonbiodegradable or more-toxic flushing agent brands may require disposal under the same guidance and expense as hazardous waste, which likely requires a hazmat company.

8. Flush in to out, high to low.Always flush from inside of the mechanical room to outdoors to prevent contamination of occupied spaces. However, in cases where the mechanical room is lower than the exterior lineset terminating area, flush from the outside to inside, covering the lineset and bucket area with a towel to minimize splattering. Cover the floor of the mechanical room with a tarp.

For the best pressure, brazing a flare tool onto the cut lineset is best, but a good substitute is a conical rubber tool that has a flare fitting connected to a small-diameter copper tube inserted into the lineset. Holding the rubber edge against the cut lineset opening gives a tight fit to prevent spillage.

9. Remember the access valve.Many technicians, especially first-time users, might forget that an access valve/charging hose or injection kit (depending upon the brand) is needed to introduce the flush into the lineset. A good wholesale customer service representative should suggest that these necessary items accompany the purchase of any pressurized, sealed flushing agent. Nonpressurized flushing agents should be avoided; their contents can introduce moisture to the linesets.

All flushes are blends of many materials. Oxygen can be introduced into an unpressurized container and break down the effectiveness of these flushes.

10. Solder a flare fitting onto the lineset.Several methods can be used to connect the flushing agent canister access valve/charging hose to the lineset. Some technicians use a conical rubber piece with a connection fitting. However, the best method to get maximum pressure is soldering a 1/4-inch flare fitting onto the end of the lineset.

11. Flush until clear.Don’t stop flushing until the terminating liquid in the bucket becomes clear and particulate-free. Near the end of the flushing procedure, replace your bucket containing the dirty flushing agent with a clean bucket so you can determine when the flushing agent is clear.

12. Conclude with a nitrogen purge.Soon after flushing, finish the cleaning by purging the lineset again with nitrogen before the flushing agent evaporates. Most flushing agents can evaporate in anywhere from 10 to 15 minutes.

Publication date:05/17/2010