Troubleshooting; Lubrication; Oil Dilution; Inadequate Suction Superheat - Emerson Copeland 2D Application Manuallines

7

Troubleshooting

The prevention of failures is one of the primary responsibilities of the installer. Otherwise the user
will not get the benefit of factory-guaranteed quality.
7.1

Lubrication

Compressors are delivered with an initial oil charge. The correct oil level is shown in Section 2.5.9
"Oil level".
Some, but not all lubrication problems are listed below:
 Oil pump-out due to high on/off cycling rate: The number of cycles should be limited to 10-12
per hour. A high cycling rate will pump oil into the system and lead to lubrication failure. Oil leaves
the compressor at start-up and the short running time is insufficient to return the oil to the
compressor via the suction side, the result being lubrication damage.
 Incorrect calculation of pipe sizes: It should be remembered that the entire system will be
coated with oil to some extent. Oil viscosity changes with temperature. More oil stays in the
system than was originally expected.
 Low gas velocity: System gas velocity changes depending on temperature and load (capacity
control). In low load conditions the gas velocity may not be high enough to return oil to the
compressor.
 Faulty or badly designed oil return system.
 Incorrect pipework.
 Leaks.
In time, lubrication problems lead to failure of the main moving parts. A standard oil pressure switch
protects the compressor against low oil pressure if the problem lasts for some considerable time.
The typical breakdown symptom of a compressor with inadequate lubrication is failure of the bearing
furthest away from the oil supply, the nearest having just enough oil to be properly lubricated.
7.2

Oil dilution

During the off-cycle a certain refrigerant concentration is always present in the compressor oil. This
depends on the compressor temperature and crankcase pressure. The rapid reduction of pressure
on start-up causes the refrigerant to evaporate from the oil. This causes oil foaming which can be
seen in the compressor oil sight glass. The oil pump draws in significant amounts of diluted oil and
foam and cannot build up oil pressure. If this cycle is repeated often enough bearing failure will
eventually occur. To prevent this type of failure a crankcase heater and/or a pumpdown system
should be fitted.
7.3

Inadequate suction superheat

The suction superheat should not fall below 10 K. Low superheat will cause valve plate, piston,
cylinder wall and connecting rod damage. Low superheat can be caused by a defective or badly
adjusted expansion valve, incorrect sensor bulb mounting or by very short refrigeration lines. If
refrigeration lines are very short the installation of a heat exchanger or an accumulator is
recommended.
7.4

Acid formation

Acid forms in the presence of moisture, oxygen, metal salts and metal oxides, and/or high discharge
temperatures. The chemical reactions are accelerated at higher temperatures. Oil and acid react with
each other. Acid formation leads to damage of the moving parts and in extreme cases to motor burn-
out. Different test methods can be used to test for acid formation. If acid is present, a complete oil
change (including the oil in the oil separator) will help. A suction filter that removes acid should also
be fitted. Check filter-dryer condition.
7.5

Inadequate compressor cooling

For some compressor models and applications, cylinder head fans can be options to improve
compressor cooling. If the fan does not provide sufficient cooling high discharge temperatures can
result. The only solution is to fit an appropriate cooling fan.
32 AGL_HA_ST_Discus_A2L_A1_EN_Rev00