Cooling Compressors

We consulted to an expert team on the repair and maintenance of the cooling compressors.
Let’s see what are their comments.

What is the biggest enemy of the cooling compressors?
- I suppose that the air in the system is the biggest enemy of the cooling compressors. It is therefore, the compressor should be evacuated if taken out of operation for long period of time. As an average, this is 36 hours in foreign countries, but 1 hour for us. The oils of the vacuum pumps should also be replaced at every 6 hours. Unfortunately, we don’t observe this rule. These oils collect the moisture. They give the moisture off in the system. I tell you that, the service dealers mostly work on the vacuum and keep the system under vacuum by using 5 to 10 vacuum pump to do that. In addition, there is a solenoid valve at the output of the vacuum pumps. This valve is for safety purpose not to waste the vacuum. There are numerous small tunnels and channels in the compressor and it takes time to evacuate the air trapped in these cavities. I repeat; the air in the system is the biggest enemy of the cooling compressors.

On the other hand, failure to perform superheating adjustment or even being unaware of such adjustment is another point to consider. There is not so much expert experienced on this matter. The compressor should be cooled with return refrigerant. This is true for all types of the compressors. All hermetic, semi-hermetic, scroll, screw and similar compressors are cooled with the return refrigerant. rT temperature difference should be adjusted for 7 – 8°C. This is the difference between the temperatures of the refrigerant at evaporator pressure corresponding to low pressure at the entry to the compressor. By this way, cooling is provided for the coil, bearings, piston and valves. I repeat; the superheat is the temperature difference of the refrigerant at the evaporator and at the entry of the compressor. It is ideal to make it 7 – 8°C. It is not easy to adjust 6°C. The control for the superheat is performed by the sticker affixed onto the return pipe.

What we see when we disassemble a compressor?
If we are a service dealer that can disassemble the compressor, we should also be able to determine the reason that caused the failure of the compressor so that it will not be sent us again for repair. That is to say, it is not wise to say: “I repaired the compressor and that’s all what I can do”. When we come to what we should pay attention, we may say that we should look at the depleted oil, valve dislocations, piston ring wear, bearing wear, coil breakage imagining their possible reasons as well. We in fact see all the stages that have given rise to the breakage of the compressor when we disassembled and see all its parts.

Would you provide us some information about state-of-art compressors?
- It is COP value that matters for us. That is, the ratio between the power consumed and work performed. In the past, Trane or similar 8-cylinder or 6-cylinder compressors had very high COP values. Now, every effort is made to reduce the amount of power consumed by the screw compressors. There will be an energy summit in 2010. The power consumption rates will be considered by assigning g Class A and Class B cooling units and the manufacturers will be certified by Ministry of Energy. The works on that is under progress.

Do you inform us about the screw compressors?
- COP values of the screw compressors are very high. They require high peak current at the startup. Where 4-stage capacity controlled compressor is switched on 5 times in a hour, it means that the startup current of it has already been very high. The compressor efficiency is inversely proportional to the interruptions.

How do compressors with invertors operate?
- There is a fixed compressor that operates continuously. There is also inventor controlled compressors. When the operation is started, the fixed compressor is operated first. It is switched of as needed. But inverter-controlled compressor is operated for its 20% capacity, up to 90%. When the capacity reaches to 90%, it is switched off; fixed compressor is started until 100%. This ensures extreme saving in power consumption.

Thank you very much to Mahmut TURGUT, senior staff, HCS (Hermetic Compressor Service).