The compressor is the heart of any air conditioning or refrigeration system, so when it starts showing signs of not working correctly, technicians must act quickly in order to find out what is wrong. But identifying the reason behind why a compressor is not performing optimally can be a challenge, because there are a variety of reasons why a problem may occur, and by the time the problem is discovered, it may be too late for the compressor.

For systems showing signs of compressor trouble, technicians should employ comprehensive troubleshooting techniques in order to isolate the problem.

Systems showing signs of a compressor problem may exhibit a variety of symptoms, said Jamie Kitchen, account manager at Danfoss, including:

If any of these symptoms occur, then Kitchen recommends performing the following troubleshooting steps:

Michael Robertson, senior account manager at LG Electronics USA Component Solutions Business, added that a locked rotor, poor cooling/heating (if heat pump), and of course, a compressor not running are all signs of compressor distress. Although technicians should follow the system manufacturer’s instructions and guidance, basic troubleshooting steps for these symptoms typically include:

“LG routinely performs teardown and root cause analysis on compressors returned and covered under manufacturer’s warranty, and typical problems include oil washout causing bearing failure, and scroll sets destroyed due to liquid entering entering the scrolls,” said Robertson. “Scrolls weren’t designed to pump liquid, only vapor.”

Randy Tebbe, application and service engineering manager at Emerson, notes that some common symptoms that are likely caused by other system issues and might interfere with a compressor operating properly are:

“Each of the above conditions can be caused by faulty system components or control set points, which is why it is critically important to correctly identify the actual cause of the improper operation before installing a replacement compressor and exposing it to the same conditions that resulted in operational issues with the first compressor,” said Tebbe.

Compressor problems are usually either mechanical or electrical in nature. On the electrical side, Kitchen said that voltage can be out of allowable range, resulting in excess current draw, which will overheat the motor and cause premature insulation failure.

“Conductors may also not be connected properly or corroded,” he said. “This can cause overheating at the compressor terminals both inside and outside of the compressor shell, and the terminal and/or conductors can be damaged and insulation burned away.”

On the mechanical side, Kitchen noted that the most common problems can include:

Isolating the problem will require specific troubleshooting steps based on the compressor type, but there are procedures that are universal for all types, said Kitchen. For example, reciprocating compressors are not affected by running backwards, but scroll compressors are and will not compress refrigerant — they will eventually overheat and cycle on the internal overload.

“Failure to build pressure with a reciprocating compressor can result from failure of the valves, so the compressor will run but not build pressure,” said Kitchen. “Current will be low as well, since the compressor is not working to compress the refrigerant. The lack of pressure differential and loud noise will indicate a scroll running backwards. A reciprocating compressor with a valve failure may not sound that different from one that is operating correctly. Checking the pressure differential and current draw will indicate the valve failure.”

Kitchen added that when starting up a scroll compressor system or a replacement scroll for the first time, it is important to note that for compliant scroll designs, it can take up to 70 hours of run time for the compressor to operate as stated in the manufacturer’s literature. This will mostly affect the current draw and, to a lesser extent, the cooling performance of the compressor, he said.

Finding the specific issue associated with a compressor problem can be challenging, which is why it is so important for service technicians to understand the system, how it was designed to operate, what the parameters are that it needs to be operating within, and how the system is being controlled, said Tebbe.

“More than one-third of compressors returned to Emerson for warranty analysis are determined to have nothing found wrong — they were simply misdiagnosed in the field as being defective,” he said. Replacing working compressors unnecessarily costs everyone, he added, so before replacing or returning a compressor, technicians should be certain that the compressor is defective by following these steps:

If the compressor has already failed, it can be challenging to isolate the problem, because with an inoperable system, gathering temperature and pressure readings is not possible. However, Kitchen noted that the technician can still:

“A failed compressor does not necessarily mean it was the compressor’s fault, which is why the technician must determine why the compressor failed,” said Kitchen. “This can often be done when replacing the compressor and starting up the system. Proper electrical checks, measuring airflow values, component capacity matching, and proper evacuation and charging can catch and eliminate the majority of causes of compressor failure.”

Robertson added, “The simple fact is that the cause of a compressor failure isn’t always apparent. The technician needs to put on his or her detective hat and investigate thoroughly to pinpoint the problem — mainly because the issue might not be the compressor at all.”

Joanna Turpin is a Senior Editor. She can be contacted at 248-786-1707 or joannaturpin@achrnews.com. Joanna has been with BNP Media since 1991, first heading up the company’s technical book division. She obtained her bachelor’s degree in English from the University of Washington and worked on her master’s degree in technical communication at Eastern Michigan University.

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