By Buzz Estes

Deciding whether a co_pressor failed because of lightning is a challenge that

requires careful analysis

D etermining whether a refrigetation com-p"r-=e·s-"-:~"':::'" sor failed because of voltage sUIige, usually

lightning, is the type of challenge that all good diagnostic service mechanics enjoy. It's rarely easy and sometimes the results are debatable, but it needs to be properly addressed. Professionalism and thoroughness are essen­tial. Sloppiness and laziness will yield an inferior and

20 years of failure analysis, a variable umber of the "failures" were electrically

often incorrect conclusion. The failure analysis of a hermetic or semi-hermetic

compressor begins at the job site or on a test bench by checking the compressor with a megger and/or ohm­meter against specifications for that compressor. If these are within the expected limits, an attempt should be made to run and observe the amperage. If the amper­age is approximately locked rotor amperage, the probability is high that it's a case of mechanical rather than electrical failure.

On single-phase units a hermetic analyzer such as the TIF 8000 is helpful in determining this. Of course, all starting com­ponents must be checked. Also, the voltage should be checked at the compressor leads during the starting cycle. Do not read the voltage at the compressor terminals with power applied because of the possibility that the terminals could explode. It's a rare occurrence, but has happened enough times to war­rant the caution.

24 RSES Journal - July 1995

echanically operational. If the com-pressor runs, e er it pumps or not, this is not a light-ning-caused fail e. the object is only to determine lightning liability, h· ·s now accomplished.

If the compresso e above test, the next step is a teardown. There is no way to accurately determine the cause of failure 1 · out it. We will not go into detail on how to do a general failure analysis here. Burl C. Brown gave many presentations through­out the country on this topic; his "Autopsy Gn a Com­

pressor" kit is required reading and a recommend­ed reference. Carrier Corp.'s slide and audio pre­sentation entitled "Why Compressors Fail" is also highly recommended.

CoNDUmNG THI IEAIlDOWN A teardown is not complete unless the compressor has been completely dismantled. A preliminary conclusion will often have to be reversed when the last evidence is found. This is a process of

elimination and analysis, and nothing must be left to chance or assumption.

Before beginning an autopsy, the compressor should be vigorously shaken so that any material settled in the sump will be in suspension and come out with the oil. The oil should then be removed, measured and saved

for future reference. The quality of the oil and its amount will give some idea of the condition of the sys­tem and quality of service it has received. Most com­pressor manufacturers publish the correct oil charge and it should be noted whether the charge removed was approximately the proper amount, less what should be in the system. This oil is regarded as a hazardous waste by several state environmental agencies and should be stored or disposed of properly. In addition, gloves and goggles should be worn when handling oil from an elec­trical failure.

The condition of the oil can help guide the teardown to the proper conclusion. Any particles observed are alien and can give an indication as to whether they came from bearings, valves, windings or trash out of the system. The color or acidity of the oil is not important at this time.

After performing the mechanical teardown, make a determination whether the original cause was mechanical or electrical. A mechanical failure allowed to persist for enough running hours will become an electrical failure, but not vice versa. A certain amount of wear is to be expected. But compressors more than 30 years old, with­

out appreciable wear and having failed · from external electrical causes are fairly common. A compressor that operates only within its design envelope will usual­ly outlast all of the other components of the system.

It's essential that the stator be removed from the rotor so that the entire stator can be examined. The voltage surge will penetrate the motor insulation at the weakest point and that can be down in a slot (see photo 1) or at the bot­tom of a vertical stator, which cannot be seen without removal. After removal, the coil should be thoroughly cleaned so that a proper inspection can be performed. The standard pressure washer used for coil cleaning will do an excellent job without destroying the evidence, if used with a little judgment and care.

There are several clues that are char­acteristic of voltage surge only. A large amount of winding wire missing from one or more localized spots with gaps in

July 1995 - RSES Journal 25

excess of 3/8 in. (see photo 3) is rather difficult to explain any other way. Another indication is that the remainder of the coil that has the failure is often bright and shiny and has not overheated. How else can it be explained that one localized part of one long strand of wire drastically overheated and the rest did not?

Be warned that metal particles that are loose and floating in the sys­tem can cause a similar failure as they imbed in the coil and chafe through the insulation varnish. This would have to be at a junction between coils for there to be enough potential present to cause a failure (see photo 4). Balls of molten metal of the same material as the winding are as good an indication as can be found. One negative indication of a lightning strike is that the winding(s) having been uniformly and thor­oughly overheated (see photo 2).

SHEDDING SOME LIGHT There are a couple of common mis­conceptions that are often heard, but not supported by the facts. One such misconception is that lightning always affects the start winding only. This may be promoted by those that incorrectly connect starting compo­nents, but it's not true.

Another erroneous belief is that the flash is so fast, there will be little blackening, soot, sludge or blackened oil. This is seldom true because the dirtiest systems are those where the flash initiated an ongoing reaction,

26 RSES Journal - July 1995

without oxygen present, which can continue for days and produces soot so thick that it builds up in strings and is quite acidic. This soot has been observed several times in conjunction with compres­sors that were thermally hot to the touch - despite no electrical con­nection for days - and is uniquely

present only after enough power was present to reach the 2,800· F ignition point.

All of the above apply equally well to hermetic and semi-hermetic compressors. For those working with hermetic compressors, the work is harder and more frustrat­ing, but a valid analysis can be done. Do not use a cutting torch to

open the shell of the compressor. It's all but impossible to do this and not contaminate the evidence. The tool of choice is a 7-in. side-angle grinder like those found in all weld­ing and steel fabricatiQn shops.

In a pinch, a circular saw with a metal cutting blade will suffice, but is not as good for many reasons. With the side-angle grinder, gloves and gog­gles are essential. Also watch where the "sparks" are directed because they can start fires, pit glass and cause eye injury from several feet away. With the edge of this tool, the outer layer of the shell can be cut at the socket junc­tion adjacent to the weld and the shell separated without getting any con­tamination into the shell.

If the stator is pressed into the cast iron body of the compressor, as in the old CL Tecumseh series, the side-angle grinder may be used to slice the cast iron so that the sta­tor may be removed. The varia­tions of construction methods pre­clude going into any more detail at this time ...

Buzz Estes is president ofW.E. Estes and Son Inc., Athens, Ala. He has been a member of RSES for more than 30 years and is a past-president of the Tennessee Valley Chapter. He also is a member of ASHRAE. For more information, call Mr. Estes at 205-232-2327. Photos are courtesy of Electrical Apparatus Service Association Inc.