Welcome to the PROBLEM PAGE.

We find many people request assistance in the practical aspects of the industry. In response we will investigate the problem and endeavour to present the best possible solution.Thank you for all your questions sent in. Send your problems (and sometimes your creative solutions) to acra@netactive.co.za with problem page in the subject line. You may include pictures.

Gerrie Nel asks: I have taken a compressor back under warrantee to our supplier and have been told the failure was caused by liquid slugging? This created problems. What is this about and what can I do to prevent this from happening?

Gerrie, thank you for your question. Yes this will cause problems when submitting a claim for a failed compressor.Suppliers often refer to poor installation practice (Pipe work, evacuation, brazing). In addition, in many cases a technician will replace a compressor neglecting to determine the cause of the initial compressor failure. If a compressor fails due to system malfunction, the system faults must be corrected to prevent repeat failures.

I will look into three areas relating to your situation, namely refrigerant flood back, flooded starts, and liquid slugging.I will extend the answer to include lubrication issues as the effects are equally devastating.

REFRIGERANT FLOODBACK

This is a result of liquid refrigerant returning to the compressor during the running cycle. The oil is diluted with refrigerant to the point that it cannot properly lubricate the load bearing surfaces.

Damage to compressor:

In air cooled compressors we may find worn pistons and cylinders but no evidence of overheating. In refrigerant cooled compressors we may find centre and rear bearings worn or seized. Evidence of rotor drag and / or stator damage. A progressively scored crankshaft and possible worn or even broken connecting rods.

Bearing seized on crankshaft.

Cause:

The liquid refrigerant dilutes the oil in the crankcase and the refrigerant rich oil will be pumped to the connecting rods and the bearings through the crankshaft. As the refrigerant boils off, there will be insufficient oil for effective lubrication of the bearings furthest from the oil pump. The centre and rear bearings may seize or may wear enough to allow the rotor to drop and drag on the stator. This may cause the stator to short electrically.

Correction:

• Maintain proper evaporator and compressor superheat.

• Correct abnormally low load conditions.• Install accumulators to stop uncontrolled liquid

return.

FLOODED STARTS

This is the result of refrigerant vapour migrating to and condensing in the crankcase oil during the off cycle.

Damage to compressor:

Worn or scored connecting rods and or bearings. Seized bearings. Possible broken connecting rods and erratic crankshaft wear or seizure pattern.

Experiencing problems of a technical nature, drop us a line at acra@netactive.co.za with problem page in the subject line.

Problem PageBy Grant Laidlaw

Worn bearings and crankshaft scoring.

Cause:

When the compressor starts, the refrigerant diluted oil cannot properly lubricate the crankshaft load bearing surfaces.

Correction:

• Locate compressor in warm ambient or install continuous pump down.

• Check crankcase heater operation.

LIQUID SLUGGING

The compressor trying to compress liquids (Oil and Refrigerant).

Damage to compressor:

Broken reed valves and connecting rods, damaged pistons and crankshaft. Head gaskets leaking.

Broken connecting rods and pistons

Cause:

This is the result of trying to compress liquid refrigerant and / or oil, in the cylinders. Slugging is an extreme flood back in air cooled compressors and a severe flooded start on refrigerant cooled compressors. As the liquids cannot be compressed in the cylinders, damage occurs as the pistons move upward trying to rapidly force the liquid through the valves. Besides the possibility of breaking the valves, if the liquid cannot be forced through the valves in time, the next weakest point is often a connecting rod.

Correction:

• Maintain proper evaporator and compressor superheat.

• Do not charge liquid through the compressor.• Correct abnormally low load conditions.• Install accumulators to stop uncontrolled liquid

return.• Locate compressor in warm ambient or install

continuous pump down.

Gerrie, there is in addition to the problems that I have outlined one more situation worth looking into. This situation is the refrigeration technician dumping quantities of liquid refrigerant (during charging) into a compressors suction that has not been designed to pump liquid. This is typically done to save time. I have been informed on the odd occasion that as long as the compressor does not make too much noise whilst pumping liquid that this is OK. This is not OK!!!The possible damage caused is similar to the problems mentioned above.

LOSS OF OIL

Insufficient oil in the crankcase to properly lubricate load bearing surfaces.

Damage to compressor:

Uniform wearing or scoring of all load bearing surfaces.Uniform wearing or scoring of crankshaft.Damaged broken pistons, connecting rods and components due to seizure.

Seizure on crankcase journal

Destruction of compressor components due to lack of lubrication

Correction:

• Check refrigerant charge.• Use correct oil type and viscosity.• Check system piping for incorrect sizing and oil

traps.• Check oil separator• Check oil safety control.• Correct abnormally low load conditions or short

cycling.• Check for inadequate defrosts.

Here again I have seen some strange situations, from adding vacuum pump oils to a system to the use of oils used by the motor industry.

I hope that this sheds some light on the problems highlighted and saves you the stress associated with compressor warrantee claims.

REFERENCES:

Special thanks to:Cassie SteenkampReferencesPower Compressor Exchange www.compressorexchange.com

Thanks to all for writing in with interesting questions. Looking forward to hearing from you – Grant Laidlaw