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HVAC Service Tips on Flushing Linesets and Burnouts

Flushing linesets is a preventative 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.

When to Flush

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

How to Flush

The best service practice is to remove the linesets altogether along with the system components.  However, in many cases this may be impossible or cost prohibitive when linesets are under concrete or recessed in walls.  Therefore, technicians have no choice but to clean the linesets.

12 Tips

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

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. 

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-lb. canister of flush for a 7-to-10-ton refrigeration system. Extremely contaminated lines may need more than 2-lbs of flush. Since most flushing agent brands are sold in either 1-lb. or 2-lb canisters with the latter a better price value, it’s more economical to flush a 5-ton system with half of a 2-lb. canister. 

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

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, 100-feet or longer should be cut, flushed in sections, and then soldered back together. 

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

Collect the debris. A bucket should be used 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 MSDS (Material Safety Data Sheet). Biodegradable flushes require the same disposal as used refrigeration oil. However, non-biodegradable or more toxic flushing agent brands may require disposal under the same guidance and expense as hazardous waste, which likely requires a hazmat company.

Flush in to out/high to low. Always flush from inside of the mechanical room to outdoors to eliminate contaminating living spaces. However, in cases where the mechanical room is lower than the exterior lineset terminating area, flush from the outside to inside, but cover the lineset and bucket area with a towel to minimize splattering. The floor of the mechanical room should be covered with a tarp.

Remember the access valve. Many technicians, especially first time users, might forget 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 these necessary items accompany the purchase of any pressurized, sealed flushing agent. Non-pressurized flushing agents should be avoided because 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.

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 ¼-inch flare fitting onto the end of the lineset.

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 to help determine when the flushing agent becomes clear. 

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 anywhere from 10 to 15 minutes.

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.

By Ross Soyka-Director of Marketing, Mainstream Engineering

BIO: Ross Soyka is currently the director of marketing for the QwikProducts Division of Mainstream Engineering, Rockledge, Fla. Most QwikProducts have been developed under U.S. military or NASA R&D contracts and feature products such as QwikShot, an acid eliminator, QwikCheck, an acid test kit, Qwik- System Flush,a flushing agent for refrigeration systems as well as other service-oriented products for the HVAC/R field technician. Upon request, Soyka presents flushing practices and other refrigeration service procedures at trade association meetings and wholesale distributor seminars. He can be reached via email at or +1 321-631-3550.

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