(Information in this post was provided by Bruce Porter, Manager UPG Field Service. Bruce has written many application bulletins for UPG and is well-respected for his expertise in the HVACR field. He also teaches HVACR at Metro Technologies Center HVAC)
The leak repair process for split systems & package units are the same, and are described in this procedure. It is important that proper diagnostic tools be used to determine the source of leaks. This procedure is therefore written in two parts “Leak Detection & Repair” and “Recharging Procedure”. To properly diagnose the location of a leak, always use high pressure nitrogen (400 psig) and an electronic leak detector or soap bubbles to confirm the leak location.
Note most R-410A systems use highly hygroscopic “POE” lubricant oil, which means it absorbs moisture at a high rate when exposed to the atmosphere. For that reason, care must be taken to minimize the time the refrigerant system is open and to maintain proper nitrogen charge during repair. As part of the repair, new driers must be installed to capture remaining moisture left in the system.
If the outdoor unit is being repaired due to a compressor burnout (possibly caused by a refrigerant leak), it is likely that additional contamination is present in the refrigeration system. In this case, a 100% activated alumina suction-line filter drier is required to purge the system of the additional contaminants and acid.
Additional steps are required to install a suction-line filter drier and purge the system of additional contaminants and acid.
Leak Detection & Repair
Step 1 – Verify system integrity by checking system pressure. Use a manifold gauge set to see if the system is still under pressure or if it is empty and void of charge. If the system is under pressure you may be able to leak check with the charge left in the system using bubbles or electronic testers. If not, the remaining charge must be reclaimed and disposed of or reused per EPA regulations. After reclaiming the remaining refrigerant, note the weight removed. Reclaim to about 2 psig and directly introduce nitrogen under high pressure on top of the leftover refrigerant pressure, then test the system with 400 psig dry nitrogen. At this time, access the evaporator section to check for the presence of refrigerant. In most cases you will be able to hear the leak if it is an obvious one. Look for signs of oil as R-410-a and oil bond, a leak will leave an oil trail. If system is void of charge and under nitrogen pressure, the leak cannot be either heard or visually seen then you must use an electronic leak detector.
Step 2 – Electronic Leak Detection. If the system is void of refrigerant and the above step yields no leak that can be seen or heard, use of an electronic leak detector is mandatory. Introduce 2 psig of refrigerant and increase pressure with nitrogen to 400 psig. This is required so you will have a tracer amount within the system so the detector can register a leak. Release of this tracer gas combination is considered a diminimus release.
Step 3 – Pinpoint leak location. When the leak is found, use soap bubbles to get a pin point location. You might need an inspection mirror along with a bright flash light to accomplish.
Step 4 – Repair the leak. If the leak is in the tube sheet of the MicroChannel coil (aluminum portion) the technician has the option of replacing the coil or repairing the coil using an aluminum repair kit available from Source One. If the leak is in the copper bearing portion of the system, then a 5% Sil-Phos/Silver may be used along with nitrogen purge at 1psig during this operation. A leak at the copper-aluminum joint should never be repaired in the field as this braze joint requires sophisticated process controls not normally available in the field. Such a leak requires a coil replacement.
Step 5 – Remove the original factory filter drier in the condensing unit, then install a new liquid line filter drier.
Step 5b – Add suction-line filter – If the refrigerant system was opened to replace a compressor burnout, then a 100% activated alumina suction-line filter drier must be installed. After the system is operational, additional steps are required to run the system until contaminants are removed
Step 6 – Confirm leak repair. Pressure test the system (400 psig refrigerant tracer gas) and leak check with soap solution or electronic leak detector. If leak is still present then repeat previous steps until leak is repaired.
Step 7 – Introduce calculated charge volume addition. Slowly open suction manifold valve and monitor refrigerant scale until volumetric charge adder is met. Remember to reduce charge adder by 3 ounces from the total calculated value to account for the charge present in the gauge hoses (assuming two 3 foot gauge hoses) to avoid overcharging the system.
Step 8 – Validate charge value is correct and system is operating properly. Continue to monitor the system until stabilized, typically 10-15 minutes. Please refer to the charging charts on the condensing unit to determine proper subcooling (for TXV applications) or superheat (for orifice applications). The charts are based on outdoor ambient conditions.
Step 8b – Removal of contamination/acid from compressor burnout. If the refrigerant system was opened as a result of a compressor burnout, additional steps are required to ensure absorption of contaminants left in the system. Run the system for 10 hours, then monitor the suction line drier pressure drop. If the pressure drop exceeds 3 psig, replace suction line filter drier and re-run the system for another 10 hours. If the pressure drop is less than 3 psig, remove the suction line drier, and perform an acid test. If the test shows no presence of acid, remove the suction filter dryer and close system. Re-establish system integrity by performing high pressure nitrogen leak check.
If the acid test shows acid still present in the system, replace suction line drier and re-run the system for another 10 hours. Repeat this process until acid is not present in the system.
Note that the suction filter drier can be run for more than 10 hours, but never leave the suction line drier in the system for over 50 hours of operation as this could lead to further contamination and compressor failure.
Step 9 – Record your data. Record the total system charge and date on inside panel. This should be done adjacent to wiring diagram. This will be useful for the next service technician. Document required startup & commissioning data in factory provided startup sheet.
If these procedures are followed, the operation and reliability of a system with R-410a refrigerant and P.O.E. oil will not be affected and should provide many more years of service. These procedures apply to both tube and fin coils and MicroChannel coils.