Converting residential air conditioning equipment that uses R-22 to a replacement refrigerant is seen by many contractors and homeowners as a good way to extend the life of the system while removing R-22 from the picture. There are a number of replacement refrigerants to choose from, but with any replacement, it’s important to remember that the refrigerant is only half of the equation. Care must be taken to ensure the proper lubricant for the replacement refrigerant is used. Following the proper conversion procedures — especially when a lubricant change is required — will help ensure a successful conversion.

One of the most commonly used replacement refrigerants is R-407C. R-407C closely matches the performance characteristics and capacity of R-22; however, it’s a pure hydrofluorocarbon (HFC) refrigerant. When converting a system originally designed for the refrigerant/lubricant pairing of R-22 and mineral oil to a pure HFC refrigerant, such as R-407C, it is critically important at the same time to completely change the lubricant to an approved polyolester (POE)-type oil, said Chuck Allgood, refrigerants technology leader, the Chemours Co.

Allgood explained that mineral oil is fully miscible with R-22 and is a good lubricant, but it is not miscible with HFC refrigerants, such as R-407C. POE lubricants, meanwhile, are fully miscible with HFCs but cost more, tend to absorb moisture, and act as solvents to loosen deposits or sludge in old systems, which potentially cause problems. Miscibility is important as it keeps the oil viscosity low (due to dissolved refrigerant), which helps keep it flowing even at cold temperatures and prevents separate layers of oil or refrigerant from forming in the system.

All compressors discharge and circulate some oil out into the system during normal operation, and a combination of the oil/refrigerant miscibility and the gas velocity typically serve to push the discharged oil around the system and back to the compressor where it belongs (oil return).

“Using pure HFCs, such as R-407C, without changing the mineral oil to POE could quickly lead to a lack of oil return, which would have severe impacts,” Allgood said. “Lack of oil in the compressor could cause a system to shut down if the system was equipped with protection devices, but more likely it would be a mechanical failure due to a lack of lubrication, such as bearing seizures, overheating, etc.

“Even if the minimal oil level could be maintained in the compressor, residual oil out in the system could become trapped (logged) at low spots or cold surfaces, such as the evaporator coils,” he added. “Oil-coated coils would severely degrade heat transfer and lead to poor performance both in ability to cool [capacity] as well as increased energy consumption and run time [efficiency].”

Historically, compressor manufacturers have required that conversions from R-22 to R-407C need more than 95 percent POE in the system; in some cases, more than 99 percent POE is called for where enhanced surfaces exist in the system (enhanced surfaces are very small features, such as ridges or grooves that are machined into the inner and outer surfaces of coil tubes that increase surface area and help initiate condensation). Allgood pointed out that getting to less than 5 percent — or 1 percent — residual mineral oil likely requires three flushes or oil changes, which, for many systems, is not easy, convenient, or cheap.

“Some folks have tried to cheat the process with no or minimal oil changes, which can be directly related to poor performance — which end users may or may not notice — or equipment failure, which would be pretty obvious,” Allgood told The NEWS. “Chemours’ position is aligned with that of major compressor OEMs: for all pure HFC refrigerants, such as R-407C, a full (greater than 95 percent) oil change from mineral oil to POE is required.”

He added that this applies to conversions to pure HFCs. There are some refrigerants — Chemours’ Freon™ MO99 (R-438A) is an example — that take a different approach and incorporate small amounts of a hydrocarbon (HC) into the refrigerant itself. The small amount of HCs are not enough to cause the blend to reach a flammable concentration, as R-438A and other products that contain a small amount of HC are ASHRAE classified as nonflammable (A1). However, they do aid in mineral oil return and eliminate the need for a full oil change to POE in most cases, especially in residential air conditioning systems.

ON BOARD WITH POE

Jeff Salisbury, product manager, North America, Tecumseh Products Co., said that as the availability of R-22 has declined, and the price has increased, Tecumseh has been updating its service guidelines to encompass the myriad of replacement options.

“Previously, we released specific models that were dual-rated for R-407C and R-22, because that was the OEM replacement of choice for R-22 reciprocating compressors,” Salisbury said. “But there are literally dozens of options out there now. If you’re going to capture the cross-section of replacement refrigerants, POE is the best choice in terms of lubricant performance and flexibility regardless of market or regulatory influences.”

Todd Bexten, an applications engineer at Tecumseh, noted that many of the replacements state they’re compatible with all three oils: mineral oil, alkylbenzene, and POE. He said Tecumseh has tested some – but not all – of the replacements and has found that to be true for the most part.

“There does not seem to be a problem with oil return as long as the system is retrofitted properly,” he said. “At this point, we’ve gone across the board with POE oil for retrofits in all of our reciprocating R-22 compressors. When we review our options with respect to system compatibility, performance, and compressor reliability, POE is the best encompassing lubricant to cover the various R-22 replacement refrigerants.”

Bexten added that POE oil can act as a solvent in less-than-clean systems, such as systems that have experienced a burnout or that simply have not been maintained over the years. POE may dislodge debris in the system, which can lead to plugged liquid line filter driers or contamination coming back to the compressor. However, it should be fine for clean systems, he said.

PAY ATTENTION TO MASS FLOW

Maureen Beatty, executive vice president, National Refrigerants Inc., said when converting an R-22 system to any replacement refrigerant, it’s important to check the manufacturer’s recommendations for the proper lubricant and follow the proper conversion procedures.

“The only way to guarantee you’re not going to have oil return problems is to use POE oil when moving to an HFC or to use one of the replacement products that contain an HC in which the HC thins the oil and forces it back to the compressor,” she said.

Beatty also reminded technicians to pay attention to the mass flow rate of the replacement refrigerant relative to R-22 because of the potential impact a higher mass flow rate can have on metering devices.

“In many cases, the expansion valves in air conditioning systems are fixed,” Beatty noted. “For some products with a mass flow rate higher than R-22, that could lead to issues with getting enough refrigerant into the evaporator.”

A CHANGEOUT PROCEDURE

Christopher Fogarty, assistant product service coordinator, technical support department, Lennox, provided a checklist of the essential steps to take when changing out R-22 for R-407C. Be sure to follow the manufacturer’s recommended procedure for any R-22 replacement refrigerant.

• Before starting the conversion, the system should be thoroughly leak-tested, and all leaks should be repaired before the new refrigerant is added;
• Run the compressor for at least 30 minutes under steady conditions to allow as much mineral oil as possible to return to the compressor, and record operating conditions. If mineral oil remains in the system, the compressor will not be properly lubricated and will fail, which may cause an even more expensive repair and an angry consumer;
• Cycle all power off to the system, and recover all the R-22 from the system. It is a federal law that R-22 refrigerant must be recovered and reclaimed. “Topping off” with R-407C is unacceptable. In fact, if all R-22 is not removed from the system, the system will have lubrication issues leading to a compressor failure;
• Remove the compressor from the system, and then remove the mineral oil from the compressor through the compressor suction stub. Systems that have suction line accumulators and traps must also have the mineral oil drained from them measuring the quantity of oil. It is also advisable to carry out an acid test on the lubricant removed from the compressor. Measure the mineral oil removed to ensure the correct amount of oil is replaced. Too much oil causes a loss of capacity and efficiency and increases system power consumption. Replacing too little oil results in a compressor failure;
• Flush the suction line, liquid line, and evaporator using regulated dry nitrogen to remove any contaminants and residual mineral oil. Debris from contaminated lines will foul the compressor and cause failure;
• Add a similar amount of POE lubricant to the compressor compared with the amount of mineral oil removed from the system. Once the POE is added to the compressor, the compressor should be quickly sealed to prevent moisture from entering the oil. Over time, any moisture in the compressor will convert to acid, which will damage the compressor and other system components;
• Reinstall the compressor in the system;
• Remove and replace any system filter driers. If no filter drier is present, install a new filter drier in the liquid line. Due to the properties of POE oil, installation of a suction filter is highly recommended to control system moisture to acceptable levels and to prevent debris from entering the compressor. Filters must be approved for use with R-407C;
• Pressurize the system using a mixture of nitrogen with R-407C to pressure test for leaks and to ensure a leak was not created during the conversion from R-22 to R-407C. Be sure to use leak detection equipment approved for use with R-407C;
• Evacuate the system to a maximum level of 200 microns from both the low- and high-pressure sides to remove any moisture and air/nitrogen from the system. Leaving air/nitrogen in the system further degrades system performance;
• Charge the condensing unit with new R-407C refrigerant. R-407C (a zeotropic refrigerant blend) charging should be done in a liquid state to ensure proper refrigerant composition. If the system is charged in a gas state, the R-407C will not have the proper refrigerant properties ,and efficiency and capacity will be further degraded;
• Start the system and record the operating conditions. Compare the new operating conditions with the data taken before the system conversion to ensure the system is operating properly;
• Check the oil composition using a refractometer. If the POE oil has more than 5 percent mineral oil, then the oil and refrigerant have to be removed again until there is less than 5 percent mineral oil. Again, having too much mineral oil in the system may lead to a compressor failure;
• After retrofitting an R-22 system with R-407C, tag the compressor and outdoor unit with the refrigerant used (R-407C) and the lubricant used (POE). The proper color code for R-407C is Burgundy PMS (Paint Matching System) 471. This is to ensure future service on the system is done with R-407C and POE oil and not R-22 and mineral oil; and
• Properly dispose of the removed mineral oil lubricant. Check local and state laws regarding the disposal of refrigerant lubricants. Recycle or reclaim the removed R-22 refrigerant.  

SHOULD YOU REPLACE RATHER THAN CONVERT?

Joey Brown, general manager of the service division at Tempo Air in Dallas, said Tempo avoids the issue of R-22 changeouts by not engaging in them. The company’s belief is that systems that still use R-22 are old enough to merit serious consideration for replacement rather than retrofitting.

“To each his own, but R-22 changeouts are not something we’ve ever pursued,” Brown told The NEWS. “Ever since R-410A came out 15-16 years ago, we’ve been using that exclusively, and every time we encounter an R-22 system, we always look to replace it. We feel that retrofitting a unit — even if you do it 100 percent correctly — might only buy a customer a year or two from a life expectancy standpoint.”

Brown added that another reason Tempo avoids R-22 retrofits is concerns about loss of system capacity, although this may not be as big an issue everywhere in the country as it is in Texas.

“Every air conditioning system is designed to operate with a specific refrigerant, and changing it will cause some loss of capacity,” Brown said. “We understand it’s often only a minimal loss, but when it’s 102°F outside, any loss of capacity can be important.”

Brown added that other contractors may have success with R-22 retrofits.

“We try to educate our customers and leave the decision up to them,” Brown said. “If they really want a retrofit of their R-22 system, we tell them, ‘OK, but you’ll have to find someone else who will do that.’ And, frankly, I’m sure they will.”

Publication date: 10/9/2017