Some time ago I was talking to a person from acompressor manufacturing company and he happened to mention they are unable to find anything wrong with about eight out of 10 compressors that are returned in warranty.

This is a sad commentary on the expertise of a large portion of our country’s service technicians. And what’s more, this is a lose-lose-lose-lose problem. The contractor loses because the problem hasn’t been corrected. The customer loses because changing a compressor usually results in a contaminated system where the next compressor will fail all too soon. The supply house loses because it now has paperwork to fill out and old compressors to store, and the manufacturers of the equipment and the compressors end up with scrap metal that can’t be used again.

Understand that the likelihood of a compressor failing in warranty is about the same as a teenager dying of natural causes. It happens, but is rare. Rather, when a warranty compressor actually fails it’s more likely due to poor installation or poor servicing practices. Yes, I’ve seen lightning damage, line-voltage fluctuations and input power mismatches on 3-phase compressors, but once again these are usually freak incidents.

What are some common causes for in-warranty compressor failures? If moisture (or just humid air) is allowed into the refrigerant lines, this contaminates the compressor’s internal lubricant, which can cause the motor winding to short out or it can cause the compressor to lock up. And if the refrigerant lines are improperly sized, are too long or have long vertical rises or drops, this can tax the compressor and cause it to lose all its lubricant. In addition, overcharging can cause refrigerant floodback and make the compressor lock up. Conversely, undercharging causes the compressor to run too hot.

What are the sources of misdiagnosis of the problem? Realize there is very little that can give a service tech the wrong opinion that a compressor has failed. But if he or she can’t figure out the reason for a problem, they often assume the mysterious black box in there has to be the culprit. So where you find multiple in-warranty compressor returns from one piece of equipment or several from one technician or company, the problem usually is something else that is going to be overlooked by a tech that needs help.

Refrigerant-line restrictions (clogged refrigerant filters and strainers or pinched lines) often are hard to diagnose, as are air restrictions or poor duct routing. So where compressors are replaced in these cases, the problem will still be there and the next compressor is already at risk due to internal contamination from the replacement process. And although new run capacitors don’t often fail, they also can go bad and give the impression that the compressor is locked up.

What can a supply house do to reduce the needless replacement of in-warranty compressors? It always helps to provide training and to have an in-house expert who can go out to look at what problems are occurring with systems and equipment.

More and more of the larger supply houses are bringing on such people, because not only does this reduce the returns and paperwork, but the reputation of the brands of equipment you sell will be less tarnished by the problems of misdiagnosis.