• Dennis Griffin

Your Compressor Failed? Don't Blame the Compressor

There really are no two ways about it. If a compressor fails and needs to be replaced, it’s probably not going to be cheap. But if a failed compressor is replaced without first correcting the root cause of failure, get ready to open your wallet again, because the new compressor will likely fail as well. In an estimated nine times out of ten, compressor failure is a direct result of issue found elsewhere in the system.

There are a number of common causes of compressor failure, number one being lack of lubrication. This can occur when oil has degraded due to overheating or contaminated by liquid migration, blocked from reaching the bearings, or if there is loss of oil in the system. Poor pipe design on split systems is a common reason for lack of lubrication, as it can trap oil and prevent it from returning to the compressor. Suction lines must be large enough to minimize pressure drop, but small enough to maintain required velocity for oil return. Likewise, liquid lines must be large enough to minimize pressure drop and small enough to avoid undercharging the system.

Flood-back is a problem that occurs during the running cycle when large volumes of liquid refrigerant return to the compressor through the suction pipe during the running cycle, washing oil from bearing surfaces. The resulting dilution can lead to excessive wear in bearings, pistons, cylinders, rotors, and stators. Causes include low evaporator loads, oversized equipment, faulty evaporator fans, and evaporator oil logging, among others.

Flooded starts occur during the off cycle when refrigerant migrates and condenses in the crankcase oil. On start-up, pressure falls rapidly and refrigerant explodes out of the oil into the crankcase, washing lubricant from bearings, journals and rods. Some causes of flooded starts include system overcharge, long off-cycle times, crankcase temperatures lower than the evaporator, and faulty crankcase heater.

Another common compressor-killing issue is slugging, which happens when a mass or “slug” of liquid refrigerant, oil, or mixture of both returns to the compressor, usually on start-up. Because compressors are designed to compress gas, not liquid, slugging usually results in damaged components that lead to equipment failure. Slugging can be due to a number of root causes.

Principled HVAC contractors like PJM never replace a compressor without first determining and fixing the cause of failure. Unfortunately, this is not always the case with less-scrupulous contractors. For more information on compressor failure, please contact PJM Mechanical Contractors, Inc. service department at 609-496-8696.