Don’t Blame the Compressor
Determine the source of failure before installing a replacement
If a tech arrives on a job site, discovers a failed compressor, and installs a replacement without first trying to determine the source of the failure, he or she has done a gross disservice to that customer. Generally, industry leaders say, there’s a problem somewhere else in the system that caused the compressor to fail. That problem must be identified and fixed before a new compressor is installed or another failure is likely to occur.
FIND THE SOURCE
Ninety percent of compressor failures can be attributed to problems found elsewhere in the system, said Horace Park, vice president, technology, A1 Compressor. And, serious consequences can result if technicians don’t determine the true source of the compressor failure, he warned.
“Neglecting to find the root cause of the failure of the compressor will almost assuredly result in the failure of the replacement,” Park said. “Failing to take the time to diagnose the cause of the initial failure wastes everyone’s time, from the company that built the compressor to the service technician — not to mention the added cost for another replacement.”
Don Day, sales manager, AC Component Specialists Inc., explained why the risk of short-term failure is heightened when the cause of compressor failure is not properly examined.
“If the cause of the compressor failure is not determined, there is a high risk of exposing the replacement compressor to the same conditions, which may cause the replacement compressor to fail prematurely,” he said.
To prevent a replacement compressor from failing, Mike Bruno, a technical advisor at Brainerd Compressor Inc., said it’s important for technicians to start with the right mindset.
“The installer must go in with the belief that something in the system caused the first failure, and it’s imperative to find the source of that failure,” Bruno said.
COMMON CAUSES OF FAILURE
When technicians do take the time to diagnose the cause of a compressor failure, two of the most common system problems they uncover are loss of lubrication and slugging.
According to Paul Stokes, another technical advisor at Brainerd Compressor Inc., loss of lubrication is the single most common cause of compressor failure.
“This lack of lubrication from flooding or a flooded start could result in main bearing, pump bearing, or rod bearings failing with a resulting lock-up of the compressor,” Stokes said. “The loss of lubrication can come from flooding, flooded starts, high oil temperature, loss of cooling, loss of superheat, TXV [thermostatic expansion valve] hunting that is oversized, and a Btu mismatch between the compressor and evaporator.”
Park said flooding often leads to a loss of lubrication.
“[Floodback] is refrigerant that, for one reason or another, does not boil in the evaporator and travels down the suction line and enters the compressor, thus thinning the oil out to the point where it loses its lubrication qualities,” he said.
Park reiterated that loss of lubrication causes rods and bearings to seize up and surfaces to wear to the point that the compressor locks up. He added that this should not happen if the oil safety switch is operating properly.
The second most common cause of compressor failure is slugging, Park continued.
“Essentially, a liquid, either oil or refrigerant that has been lying in the suction line or evaporator, enters the compressor, usually on startup, and can’t get out of the cylinder fast enough before something breaks — rods, gaskets, valves, etc.,” he said. “Compressors are not pumps. They move vapor. Pumps move liquids. The tolerances in compressors are too tight to pump a liquid.”
After floodback and slugging, Park said the major causes of compressor failure, in order of importance, include bad contactors, system leaks, dirty evaporators, dirty filters, dirty condensers, rapid loading/unloading, mis-wired/misadjusted controls, low superheat, and wrong oil for the system refrigerant.
While there are many potential sources of failure within a system, Stokes said the first thing a technician should check when trying to diagnose the cause of compressor failure is the system’s superheat. Then, he continued, they should check oil temperature, discharge temperature, motor temperature, motor amp/voltage imbalance, and pressure switches and safeties. (See the sidebar above for a checklist.)
Park also pointed out there is an array of information and support available to help technicians determine what problems within the system caused the compressor to fail.
“Several remanufacturers, such as A1, regularly hold seminars on compressor maintenance and compressor fault diagnosis,” Park said. “In addition, A1 offers no-cost, call-in tech support. Our technicians can almost always assist in diagnosing compressor failures.”
Once the cause of failure has been determined and a technician is ready to install a replacement compressor, it’s a good time to consider the level of maintenance necessary to prevent a future failure. While maintenance programs can often be cut back due to customer concerns about cost, it’s important for contractors to promote the value of maintenance. The smaller costs associated with maintenance pale in comparison to the larger costs of replacing a failed compressor and the associated downtime.
“Regular system monitoring and maintenance are very important factors in preventing compressor failures,” Day said. “Most failures could be prevented with regular oil analysis and system monitoring. With regular monitoring and a regular oil analysis program, the service contractor will be able to catch most abnormal conditions and may be able to correct them before they lead to a compressor failure.”
Contractors need to be up to speed on the units they are installing, added Day.
“The best advice is to set up a scheduled maintenance program that includes an annual oil analysis program and to work closely with the compressor manufacturer and the unit’s OEM to obtain as much information as possible. Educate yourself so you will know the compressor is operating within the design conditions and being controlled as it should in that unit,” he said.
SIDEBAR: COMPRESSOR FAILURE CHECKLIST
According to AC Component Specialists Inc., these are the top things a technician should consider when trying to determine the cause of compressor failure:
1. Check the oil level in the compressor;
2. Check for proper operating temperatures/pressures;
3. Check for proper suction superheat;
4. Check contact points on the compressor contactor for abnormal wear;
5. Check for proper supply voltage;
6. Confirm the unit’s controls are not short-cycling the compressor;
7. Perform an oil analysis from the compressor to look for contamination in the oil; and
8. Check for proper operation of all safety devices on the system.
Publication date: 3/28/2016