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

[Lc_shi]

It's really a strange problem.
Have you requested compressor guys to do some FA?

rgds
LC

[frank]

Sounds like a circuit blockage to me

[wambat]

Were you monitering the voltage on this system while this was going on? Was the source voltage constant or was it drooping?

[fridge51]

without being there it is difficult to diagnose, but i tend to agree with frank as it does sound like a partial blockage of the system and the unit is partially pumping over hence high discharge and low suction. were any other parts changed i.e drier, or was it just the pot?

[Vincent Yu]

Thank you for your notice. It takes me at long time to fix this unit. I can provide more informaiton about the system. At beginning, I guess there is some air or moisture in the system. So I recover the system and recharge it. It does not help at all. I also wonder if there exists circuit blockage. I check the pressure drop in the system. The high side pressure drop (from compressor outlet to the dryer) is less than 2 bars. The pressure drop in low side (from the outlet of the TEV to the inlet of the compressor) is less than 0.25 bars. So I can conclude that there is no circuit blockage, both the condenser and the evaporator are OK. After that, I recover the system again and replace the drier and the TEV. It still does not work. At that time, I really run out of all my ideas. Based on high side and low side pressure drop, I know both the condenser and the evaporator work well. I have already replaced the drier and TEV. The only thing I did not touch is the compressor. Although I did not have any reason to replace it, it is the only thing I could do. So I replace it by a new compressor. Since the compressor is hooked in the system by thread connection, it is very simple to replace it. I do not need to touch any other parts. After replacing the compressor, the system works perfectly. Each time after recovering the system, I use high pressure nitrogen to purge the circuit for about 5 minutes.

Since I recover the system many times, and when I replace the compressor, I did not touch any other parts in the system, I believe the problem comes from the compressor.

Please let me know if any other information is needed.

Thanks
Vincent

[Cofreth]

Could it be either the compressor service valve not fully backseated??

[frank]

Could it be either the compressor service valve not fully backseated??

Would that cause a blockage?

[Gary]

Each time after recovering the system, I use high pressure nitrogen to purge the circuit for about 5 minutes.

Since I recover the system many times, and when I replace the compressor, I did not touch any other parts in the system, I believe the problem comes from the compressor.

Please let me know if any other information is needed.

Thanks
Vincent

Is it possible that nitrogen was left in the system? Could that nitrogen have been removed while replacing the compressor?

It might be helpful to decribe your compressor replacement in detail, step-by-step.

It is difficult to diagnose from here, but I suspect the nitrogen is your problem, not the compressor.

[afeef]

hi
yes ,, i agree that the problem is with the compressor , precisly: the intake & discharge valves
they are not doing well,a leakage of gas or the spring of valve is weak

because the pressure build in compressor is is the act of these valves
there is some manufacturing defect in them
thanks

[dogma]

Did you split the compressor and check the internals?? I'm only familiar with hermetics so this may be way off base but......

If the suction reed wasn't fully opening and the acess port was in the case would this give u those reading????



I'm a 1st yr apprentice but I thought I'd give it a stab.

[dogma]

s#*t. I should have looked at page 2 before i replied. lol oh well least i was on the right track.....................or was I

[Gary]

Exactly so. If the system is purged with nitrogen, this should be followed by an evacuation, the vacuum broken with refrigerant, and then another evacuation, then the normal refrigerant charge. It is important to get all of the nitrogen out of the system.

[lana]

Hi there,
I agree with Gary and Mark.
If there was a compressor problem then LP would rise and HP would drop. This is the only fault which makes the two pressures act opposite each other. For other faults if LP drops then HP drops too and vise versa.
If there was a HP problem then you may have 3 families of faults:
1- Lack of condenser capacity.
2- Excess refrigerant charge.
3- Non-condensables present.
The symptoms for 2 and 3 are exactly the same and you have to do "non-condensables test" to diagnose the exact one.
Cheers.

[SHERYCOOL]

I Agre Gary The Problem Is Nitrogen Not The Comp.

[engazaym]

Hi
i agre with that evacuating the system after using nitrogen is amust

[dogma]

Gary, Is breaking a vac with refrigerant allowed in your country under regulations and Codes of Good Practice.


Yes It seems like the ideal way, but I'm pretty sure we would be fined in Australia if we did this.

[Peter_1]

Finally he said it, he's an Aussie.
Dogma, same here, not allowed to do this any longer....legally.
But what's better for the environment: let the system run with nitrogen in it or vacuum it the old fashion way and then be sure that the system is free of non-condensables?
Do you purge you hose lines?
Do you always use a recovery unit for each job?
Our job is many times the use of common sense, what the law may prescribe you.

[Vincent Yu]

It has been the practice in the past to remove contaminant and moisture by purging the system with refrigerant. But now it is not allowed to do like this. I know in some area people still use this way to clean the system. We have some repairing technicians in South America who told me they still use R502 to purge the system. For the environment reason, I do hope all the refrigeration engineers and technicians stop using it!

I follow the same procedure to purge the system with nitrogen, vacuum the system and all the hoses, and charge the system. This procedure has been used in our production line for several years. So I do not think I made any mistakes when I vacuum and charge the system.

Thanks all guys who involve in this discussion.
Vincent

[coolman]

the Copeland ZR72KC is a scrollcompressor.
These compressor do have a internal pressure relief valve on the high pressure site.
These valves do leak sometimes, and hot gas is discharged directly into the suction, giving it a high hotgas temperature and lack of performance.
This might have been the problem with this compressor

Regards Victor

[Robearbam]

It has been the practice in the past to remove contaminant and moisture by purging the system with refrigerant. But now it is not allowed to do like this. I know in some area people still use this way to clean the system. We have some repairing technicians in South America who told me they still use R502 to purge the system. For the environment reason, I do hope all the refrigeration engineers and technicians stop using it!

I follow the same procedure to purge the system with nitrogen, vacuum the system and all the hoses, and charge the system. This procedure has been used in our production line for several years. So I do not think I made any mistakes when I vacuum and charge the system.

Thanks all guys who involve in this discussion.
Vincent

How about if the system wasn't tight. A deep vac after nitrogen, still have air. ???