Trouble Shooting

[Vincent Yu]

Hello All,

Recently, I experienced an interesting thing about refrigeration system trouble shooting. I would like to share it with you, and hope you guys could give me a reasonable explanation.

Our company manufactures 5 hp chiller. The compressor is Copeland ZR72KC. TEV is Sporlan EBFVE-C-GA. R22 is used in the system. When the ambient temperature is 95 degree Fahrenheit and outlet water temperature is 50 degree Fahrenheit, the condensing temperature and the evaporating temperature should be 120 degree Fahrenheit and 40 degree Fahrenheit respectively. The corresponding pressure should be 18.9 bars in high side and 5.7 bars in low side. We have built this kind of chillers for a long time, and did not have any trouble before.

Last week, there was a very strange unit. The high side pressure was always about 23 bars. At beginning, the low side pressure is OK. But after running about 1 hour, the low side pressure was below 4.5 bars. The compressor surface temperature was a little bit higher than normal. The compressor current was normal. The cooling capacity was about ½ of the normal value. At beginning, the side glass was clear. But after one hour, I could see some bubbles in the side glass. The superheat and the suction line temperature were always much higher than normal.

I had a hard time to figure it out. Many things are tried. Finally I found the problem came from the compressor. After replacing the compressor, the system works well. Now the unit has already shipped out. But I still do not have any idea about what is wrong with the compressor. I hope you guys could give me a reasonable explanation about what happens in the compressor.

I wonder if it is possible that the compressor burns oil to generate some gas and the gas is mixed with the refrigerant (just as there are some moisture and air in the system)?

I am looking forward to hearing your comments.

Thanks
Vincent