This Q&A shares insight from Andy Schoen of Tecumseh Products Co., Joe Sanchez of Bitzer, Karl Zellmer of Emerson Climate Technologies, and Benjamin Majerus of Danfoss.
What are the most common source of problems with compressors?
Schoen: “The most common source of problems with compressors is the misdiagnosis of a compressor problem. Technicians will often confuse problems with start components, an overload, or incorrect wiring with a compressor failure. When compressor failures do occur, the failure is often the result of a problem with the refrigeration unit. These problems include: floodback, flooded starts, contamination, and operating the compressor outside of its design envelope.”
Sanchez: “I would probably say flooding/liquid control. This can be the root cause for all types of other damage such as bearing/crankshaft wear, motor failure, valve breakage, etc.”
Zellmer: “The most frequent reason for seeing a Copeland compressor returned from the field is due to misdiagnosis of system-related problems. It might be that an electric component (capacitor) or reversing valve has failed, leading a technician to assume that the compressor has malfunctioned. The majority of compressors returned to us are re-tested and they run fine. We acknowledge that no level of contractor training and experience can completely eliminate misdiagnoses; and unfortunately, many misdiagnoses lead to costly replacement of a good compressor. The second most frequent problem we see is from improper charging of the system. Both overcharge and undercharge conditions can damage any compressor. This happens more frequently in systems that have been repaired a few times already.”
Majerus: “We find that the most common problems attributed to hermetically sealed compressors relate back to the temperature of the compressor and the state of the refrigerant returning to it.
“Ultimately, it is lubrication that suffers under these circumstances. If the compressor operates too hot, the oil breaks down and cannot lubricate properly. If the refrigerant returns back to the compressor as a liquid, it can wash the oil from the bearings, causing them to wear prematurely.”
What routine maintenance do you suggest for compressors and why?
Schoen: “Hermetic compressors do not require routine maintenance. The refrigeration unit in which the compressor operates, however, should see regular maintenance. In particular, make sure the evaporator and condenser coils are clean and have proper air/water flow.”
Sanchez: “Checking the oil is probably the most important. Every year oil can be pulled and examined either visually, by an acid test, or — best of all — a full oil analysis that will report the amount of moisture and wear particles found in the oil.”
Zellmer: “The best thing you can do to your system to protect it and the compressor that drives it is to keep the coils clean — both the indoor and the outdoor coils. Changing your indoor air filter on a regular basis not only maintains indoor air quality, it also reduces the load on the compressor too. Keeping the outdoor coil clean is also critical, especially in the spring when there is a lot of lint and pollen in the air.
“Also, be sure to take advantage of any diagnostic capabilities present in the system. The compressor can be used effectively as a sensor to give a technician important insight into any early warning signs or how to more quickly and accurately troubleshoot the system.”
Majerus: “Our hermetically sealed compressors require no maintenance themselves; however, it is strongly recommended that the end user follow the system manufacturer’s maintenance guidelines to ensure proper operation. For example, condenser coils require routine cleaning in order to help reduce the condensing pressures that are required to reject heat. Cleaning of the coils not only prolongs the life of the compressor, but also ensures the proper operating efficiency for the end user. Indoor filters should also be changed as part of a maintenance program. This will help to protect against liquid refrigerant returning to the compressor due to poor airflow across the evaporator. It will also save the end user money as a result of better system efficiencies.”
Are there differences in service for various compressors, e.g., scroll, centrifugal, etc.?
Schoen: “With respect to hermetic scroll, reciprocating, and rotary compressors, service procedures are essentially the same. With three-phase compressors, care must be taken to wire scroll and rotary compressors correctly as these compressors cannot run backwards. Our reciprocating compressors, however, will run properly in either direction.”
Sanchez: “Yes. We manufacture scrolls, reciprocating, and screws. Scrolls are not very serviceable due to the hermetic nature. The reciprocating can be serviced the easiest because the oil screen, valve plates, bearing cap, and terminal plate are all replaceable. Screws don’t have as much to investigate besides the oil and bearings.”
Zellmer: “Most residential and light commercial systems are sealed systems and, if they are installed properly, should not require any maintenance throughout their entire useful life. Care should be taken to keep the coils clean for proper airflow, however. Once a system is serviced and the seal has been broken for some reason, it becomes very important to periodically check for proper refrigerant level in the system.”
Majerus: “Most compressors for our industry are designed to require no service. Yet, that does not mean that compressor reliability is consistent among all types of compressors. In commercial applications, our industry has replaced large semi-hermetic reciprocating compressors with scroll compressors. One large reciprocal is usually replaced by multiple scroll compressors. Having multiple scroll compressors improves unit reliability for the end user. If one compressor fails, the system only loses part of its capacity, whereas if a large reciprocal fails, the entire system goes down.
“In addition to this, the cost of rebuilding a semi-hermetic compressor is high compared to replacing a scroll compressor. It should also be noted that the availability of skilled technicians capable of rebuilding semi-hermetic compressors is also a challenge.”
Would you recommend a checklist for service and what would you include on the checklist?
Schoen: “Tecumseh recommends checking for proper pressures and temperatures; verifying the evaporator and condenser coils are clean and have proper air/water flow; and checking compressor running amps. If the refrigeration unit is maintaining temperature, one may argue that it is unnecessary to place gauges on the unit to measure pressures, or to check compressor running amps. I would consider verifying the evaporator and condenser coils are clean and have proper air/water flow to be a necessary check even if the refrigeration unit is maintaining temperature.”
Sanchez: “I don’t think I could come up with a detailed one-size-fits-all checklist for all of our compressors. For our size equipment, the technicians really should have a better understanding of what is going on than what can be accomplished by checking boxes. With that said, checking the operating conditions, sound, vibrations, and oil would be a general blanket statement that is worth mentioning regarding preventive maintenance.”
Zellmer: “One, keep the coils clean and two, if the refrigerant circuit is ever opened due to a component changeout or the repair of a leak, you really need to periodically check the charge level to make sure it is not too high or too low. It should not be necessary to top off the charge to achieve proper cooling. If refrigerant needs to be added every year, you may be overcharging it or you probably have a leak that will either cost you money over time or might cause a total system failure eventually.
“Three, always check the contactor to make sure that it is functioning properly. If the contactor locks ‘on,’ the system will run and run until it finally freezes up and breaks. And four, change the indoor filter on a regular basis to maintain proper airflow. For those systems with a protection or diagnostic module, acknowledge or reference any flashing LEDs that are indicating imminent faults or conditions that may be leading the compressor down a path towards failure.”
Majerus: “At Danfoss, each compressor we ship comes with installation instructions for the technician to follow. This list also includes servicing recommendations like checking superheat and subcooling to properly check the system charge. This will also provide the operating conditions for the compressor. We also supply instructions specific to compressor replacement, including proper brazing, electrical connections, vacuum dehydration, and system charging.”
Publication date: 03/26/2012