Compressor valve plate failure is usually characterized by some excessive discharged temperatures, and this is one of the parameters to measure first when compressors show signs of distress. It is important to know these causes in order to prevent such failures and troubleshoot the problems. If you don’t troubleshoot the compressor failure, a replacement compressor will suffer the same problem.
Most compressor failure occurs because the compressor performance has been affected probably due to a sudden change in the working of the system, for instance, liquid slugging.
Liquid slugging and compressor failure
Compressor technicians believe that liquid slugging is probably one of the main culprits in compressor failure.
Liquid slugging is usually caused by external factors that force liquids back into the compressor, and in the process the lubricant oil alongside the insulation system are affected badly, causing the eventual breakdown of the compressor system.
In most cases, the entire system has to undergo a complete cleanup in order to remove the slugging issue.
Evaporator motor dysfunction as a cause of compressor failure
Compressor technicians also believe that evaporator motor malfunctioning is probably one of the common reasons why compressors fail.
If there is a displacement of the evaporator fan motor, there will be a partial loss of heat transfer and this may force liquid refrigerant to return into the compressor, and such may lead to a chain of other problems.
When the liquid refrigerant is forced back into the compressor, the compressor motor insulation will become less effective over time.
This may trigger compressor motor failure. Liquid refrigerant also pushes the compressor oil out of the compressor, and this may lead to lubrication issues.
The compressor will eventually cease to work when liquid refrigerant is responsible for a dysfunctional evaporator motor.
Burned-out motor as a major cause of compressor failure
A burned-out motor is another issue that can trigger compressor failure.
An adequate examination of a compressor valve can reveal if there is a burned-out motor that will contaminate an entire compressor system, and such problems will require a time-consuming cleanup.
The technician must install a liquid and suction line filter dryer that will suck out the remaining acid and moisture in the damaged system before any replacement.
Whether the compressor has failed as a result of a motor burn out or slugging of the liquid, certain recommendations apply when resolving this issue.
For instance, the temperature of the system must remain within the range of the original design. The system may have to be adjusted if the design boundaries of the compressor valves have been exceeded.
Abnormal discharge temperature problems and the effect on compressor efficiency
When a discharge valve does not seat properly as a result of damage, it will cause the lowering of the head pressure.
The unsolicited lowering of the head pressure will force the refrigerant vapor out of the cylinder, into the discharge line.
On a downstroke, the same refrigerant will move back into the discharge line and will be drawn back into the cylinder because the discharge valve is no longer seated properly.
The short cycling of the refrigerant will eventually cause the heating of the discharge gases over and over again. This then leads to abnormally high discharge temperatures.
If this valve problem reaches a point where there is hardly any refrigerant flow rate in the compressor system, then there will be a lower discharge temperature that will force the compressor system to shut down eventually.
When a discharge valve is exposed to abnormally high temperatures, there will be carbonization effect on the oil on the valve, alongside the valve plate and the valve backings.
The iron inside the valve will be forced to quicken certain chemical reactions when they have been exposed to overheating problems.
Excessive heat generated from the compressor system may also lead to contaminants being formed on top of the valve plate due to effects of excessive heat.
The oil that is broken down will eventually react with the refrigerant of the compressor system to form a sludge.
Retrofit compressor conversions and how they cause compressor failure
When a replacement compressor is not available, a technician may decide to upgrade to a newer or different model. This is “retrofit conversion.”
This may result in compressor failure and it can occur from multiple possibilities.
Technicians installing the replacement must ensure that the geometry of the new compressor is equivalent to the original one. This will ensure it fits into the new system.
Compressor valves can also become inefficient for several other reasons, these include:
▪ Refrigerant migration issues
▪ Refrigerant flooding issues
▪ Flooded starts
▪ Acid and sludge building up in the deteriorating parts of the compressor system
▪ Wrong TEV setting resulting in too little super-heat
▪ Loss of lubrication
▪ Compressor too low on oil
What is the service checklist for a faulty compressor?
There are certain checklist every technician must use when troubleshooting compressor problems, these are:
▪ The temperature of the compressor discharge must be 220 F
▪ The temperature of the condenser outlet must be 75 F
▪Evaporator outlet temperature must be 25 F
▪ The temperature of the compressor inlet must be 55 F
▪ Low-side and High-side pressures must be 11.6 psi, and 95 psi, respectively
▪ The condenser split temperature must be 10 F
▪ The condenser sub-cooling must be 10 F
▪ The evaporator superheat must be 15 F
▪ The temperature of the compressor superheat must be 45 F
The technician must pay attention to symptoms such as higher than normal discharge temperatures, low amp draw, and higher than normal suction pressures.
Conclusion
Compressor valves are very sensitive components that must be constantly checked and monitored because of their sensitivity to temperature, pressure, and external influences.
The quicker a technician discovers that something is not right, the easier it will be to fix the problem.
Regular servicing is perhaps the best possible way to avoid most problems associated with compressor failure.