Tech Tip: Flushing Refrigerant Lines For Use with R-410A

by Kevin O’Neill

When you replace an air conditioner or heat pump and upgrade from R-22 to R-410A, the ideal solution is to replace your refrigerant lines. This is because the mineral oil used in R-22 systems is not compatible with the new R-410A refrigerant and oil. (Note that about 3 to 5% of the compressor oil is circulated through the system, with the rest remaining in the compressor.

R-22 is a hydrochlorofluorocarbon (HCFC) with an affinity for mineral oil, because of the chlorine atoms in the refrigerant molecule. R-410A is a hydrofluorocarbon (HFC) and it has no affinity for the mineral oil. There’s no chlorine in it, so the mineral oil in the system (refrigerant lines) that’s left over from the old system tends to hang up in the refrigerant lines and the new indoor coil. This reduces efficiency by reducing heat transfer in the coil. It can also cause unwanted chemical reactions with the new refrigerant.

R-410A uses synthetic oil called polyolester (POE), which is chemically derived from an alcohol. Moisture left in the system with the old oil breaks the new oil down and it changes back to an alcohol, ruining its lubrication properties, causing the new compressor to fail.

Customers would go through a real hardship to replace refrigerant lines, so some companies have developed flushing agents to remove the old oil and other contaminants from the refrigerant lines. Technicians can flush the lines by cutting the indoor coil loose, and then soldering the lines together indoors. Next, we inject the flushing agent into the liquid line port outside, with a hose connected to the vapor line port outside. The hose connected to the liquid line port outside discharges into a bucket or other container. We follow the flushing agent with nitrogen under pressure to make sure the flushing agent and contaminants are forced out of the system into the bucket. After the flush, we pull a vacuum on the system with a vacuum pump to evaporate any flushing agent left as well as to remove the nitrogen and any remaining air or moisture.

Flushing lines may not be absolutely necessary in all cases, but it’s inexpensive insurance against problems, similar to installing a new liquid line drier every time you open the refrigeration system.

Kevin O’Neill, CM, is the co-owner of O’Neill-Bagwell Cooling & Heating, Myrtle Beach, SC. He has 31 years experience in the HVAC service business, is a 24-year member of RSES, and was a finalist in the 2005 NATE Certified Technician Competition. Kevin can be reached at 843/385-2220; email koneill@ sc.rr.com.