The main causes of excessive heating of a compressor can be the following: a very high compression ratio (low suction pressure and high discharge pressure), a low refrigerant charge, an operation below the permitted capacity reduction limits.

The oil temperature is measured on the outer surface of the sump on the delivery side; the discharge temperature can be measured on the delivery line at about six times the diameter of the pipe itself from the compressor.

Measurement of these temperatures must be performed on smooth and clean surfaces, free from traces of paint, rust, etc.

To obtain a good reading the thermometers or thermocouples must be kept in close contact with the surface to be measured and be isolated. When performing these checks, it must be taken into account that the measurements cannot be accurate due to conduction losses in the metal.

The process of dissociation of the oil develops within a wide range of temperatures and depends on many other parameters, in the range of temperatures indicated, however, this dissociation of the oil occurs and develops in an accelerated manner.

A high compression ratio is generally attributed to problems arising from the condenser, from the evaporator, from the regulation system or sometimes from all these together. In this case it must therefore be checked whether the condenser and the evaporator are clean, and check both the water and air flow rates on the heat exchangers, and the inlet and outlet temperatures of the water and air. The regulation system must also be checked to ensure that no anomaly causes a reduction in the refrigerant flow rate.

A low charge of coolant is also characterized by the disappearance of bubbles at the control glass of the expansion valve from a low suction pressure and excessive overheating of the sucked gases. The solution to these problems obviously consists in adding other refrigerant to the system, after having established the origin of this charge too low and repairing any leaks.

Finally, a reduced power operation, beyond the limits set by the manufacturer for certain suction and delivery temperature ranges, can reduce the refrigerant flow rate which is necessary for adequate cooling of the compressor. It is therefore advisable to refrain from the limits prescribed by the manufacturer with regard to the discharge of the compressor under certain conditions.

A correct diagnosis of the origins of a fault (and this not only in the field of refrigeration machines) not only makes it possible to restore normal conditions in less time, but it is crucial in preventing the failure from happening again.