Copeland tandem compressors over amping.

[acguy951]

Having a problem with copeland tandem scroll compressors. The compressors are over amping and tripping breakers in machine. They will run but the amps at startup are 100 + then fall back to 60 amps then gradually climb to over 100 amps before tripping breakers. Checked subcooling and superheat. 12 degrees SC & 17 degrees SH. The compressors also sound like theyre binding up inside sometimes. The oil color is light gray. Plan on having oil analysis performed. This is the second set of compressors replaced on a just installed new 60 ton Mcquay air cooled condensing unit. The 2nd circuit of compressors on the machine have no problems. We removed 2 o6e compressors and water cooled condensers and a cooling tower. This was a retrofit from R-22 to R407C. We drilled holes at the bottom of the refrigerant traps located at the air handler and tried blowing out and residual mineral oil. Checked txv's and they are labeled for R407c or R-22. Hooked up nitro during brazing. When we had the first set of compressors doing the samething we turned to our local reps service dept for answers. We never got any feedback and were given new replacment compressors. Hoping we can save these!

[ryan1088]

The oil color really bothers me. Did you already get the oil sample out? Have you tried changing the oil in the sumps?

Also what are the RLA on the compressors?

[acguy951]

I plan on doing oil analysis on monday. I did drain some oil. That was when I noticed the color. The RLA are 58 amps. Changing the oil in the compressors is going to be my first attempt at saving these along with changing drier and flushing system.

[hands]

Sounds like there is metal in the oil and the compressors are damaged from a lack of oil. I would say you will be replacing them soon. It could be there was still mineral oil in the system. What is the oil pressure and how does it compair to the compressors that are running good. After adding the 407c was there any leaks. If so you would have to recover the charge and add all new.

[ryan1088]

Metal in the oil is what I was just sitting here thinking. What was the oil level in the crossover tube?

[ascj]

Is this a 2 circuit condenser with 2 sets of 2 scrolls?
I have never seen that from McQuay is R407C.

[acguy951]

Metal in the oil is what I was just sitting here thinking. What was the oil level in the crossover tube?

The compressor oil level was half way when they were off. While running one compressor the sight glass was full when both compressors run they both are below the halfway mark on the sight glass. Oil is a milky gray. When we changed the first compressors the oil color was normal. I did perform acid test on oil and refrigerant. No acid.

[ryan1088]

That doesn't seem too out of the ordinary. You have a real mess on your hands....

[socotech]

Grey oil. Sounds like aluminium in the oil.

[GoColts]

What are the refrigerant pressures doing when the amps climbed? When these compressors were installed was the system properly flushed and cleaned? The milky color in the oil could be moisture, there is definitly metal in the oil. You should get you answers with an oil sample.

[Push It]

What is the amperage draw of the other compressors on the second circuit? If you are drawing 60 amps on a RLA of 58, with all else you descibed you are changing those compressors. What was the ambient, head pressure at time of amperage readings? I would look at your piping and verify that with 407c you have the correct velocity for oil return with the staging. How many stages of cooling is there? You stated 1 compressor does run at once. What about your air flow? What kid of AHU system is it? Constant volume? VAV?

Good luck man I agree with Ryan

[flange]

go to the parts store and buy a bunch of oil and driers. start cleaning the system up. in the meantime, ask whomever did this if they considered the effect of going to a higher condensing temp when they sized it....

[jayguy]

...The oil color is light gray. Plan on having oil analysis performed...

save your money and time on the oil analysis. your compressors are toast. there is a lot of clean up to perform now and you can not do it with these compressors as they are just filling the system with more garbage.

[alcomech]

It sounds like you have a serious issue with the design and layout of the refrigerant piping. More than likely if the piping has been improperly sized it has resulted in the lack of oil return to the compressors. Usually this problem will be the result of a low load condition and will dramatically increase when compressor‘s are staged off. This will result in low velocity of refrigerant through the system as previously stated by others. It is the velocity of refrigerant that brings back oil at an equal rate as it leaves the compressor. There are many things to consider when designing the piping arrangement, such as capacity of all components and correct size of pipe so as to maintain a certain pressure loss throughout the system and also maintain velocity. Velocity usually should not be less than 1000 FPM for suction lines. As for the liquid line it is important to maintain pressure loss at no more than 45 PSI so as to maintain sub cooling and if exceeding this pressure it is certain that flash gas will be present before the TXV.

Do you have a two circuit system; each with tandem compressors…..but it’s not clear how many TXV’s you have per circuit. It is important to properly adjust superheat settings and if not set correctly as you know will result in flood back of refrigerant which will wash oil from bearings. Verify the safety margin of the TXV’s and that it is feeding correctly. If using the same TXV verify that superheat has been increased to compensate for the higher temperature Glide.

The superheat will be lower with 407C compared to R-22 if using the same TXV.
Remember that 407C has a high temperature glide of 10 °. The setting of the TXV using R-22 and the initial super heat setting above the saturated temperature was say 10 °. Now with the blend of 407C the same evaporator temperature is achieved - but now this only provides 2 ° F of superheat above the blends vapor temperature.

Refrigerant blends need two columns pressure/temperature charts:
Zeotropic Blends have different temperatures for saturated liquid and saturated vapors at constant pressure.
•Bubble Point (or Liquid) gives pressure for saturated liquid; used as the reference point for sub-cooling calculations.
• Dew point (or Vapor) gives pressure for saturated vapor; used as the reference point for superheat calculations.

407C has a slightly lower discharge temperature, so you will need to ensure that the TXV has sufficient capacity in low ambient condensing temperature which is expected in the winter months. If the system utilizes fan cycling or head pressure control valves and fixes the minimum condensing temperature at say 70 ° (140 psi), the TXV capacity will need to be considered at this condition.
Sometimes the addition of a hot gas by-pass will improve oil return when under a part load. You may want to consider adding a suction accumulator. At start up and after a long period of down time it is likely for refrigerant to condense in the evaporator and suction line which will result in slugging at start up. But now we are getting technical and that’s a long story for another day. Be sure to install a suction filter drier.
Is the condenser located above the compressor and have you considered the net lift or drop. Also what about the evaporator? Are there traps in place for oil return where needed? What is the developed length from compressor to condenser and from condenser to the evaporator?

Troubleshooting is not part of the repair…understand the symptoms and you will find a solution.

[jayguy]

...Velocity usually should not be less than 1000 FPM for suction lines. As for the liquid line it is important to maintain pressure loss at no more than 45 PSI so as to maintain sub cooling and if exceeding this pressure it is certain that flash gas will be present before the TXV...

please be careful quoting numbers like those above...there are so many variables. i know of instances where < 200 fpm in the suction line was the most perfect choice...and places where 1000 fpm was not enough to bring the oil back in all cases.

...Is the condenser located above the compressor and have you considered the net lift or drop. Also what about the evaporator? Are there traps in place for oil return where needed?....

traps in the suction or discharge line can be very dangerous if not sized or installed correctly. even if they were, many compressor these days (including scrolls) hold so little oil that you could fill the traps and not have enough oil for the compressors. then when all of the compressors come on, you slug the compressors with oil since there isn't enough room for the extra oil. i prefer oil separators in difficult situations.

i agree on the suction filter drier. i think an oversized (and properly installed) suction line filter drier is very important at this point as well.

[alcomech]

I understand, just throwing out some ideas.

[Mrak]

Been there, done that......
If and when you change the compressor don't be surprised if they recommend and send you a pipe changing kit. The two compressors are in parallel correct? If so, they may possibly have you change the oil pipe connection from where it may be, high on the compressors and they may have you put caps on those ports, take out the sight glass on the compressor and put a new line lower, screwed in at the old sight glass threads.

I may be completely off the mark here.
But if they do indeed have you do that, in my little mind it tells me that they know they had a design problem and the oil wasn't getting to each compressor evenly and the one suffered to the point that it messed up the bearings to the point that you are at now.

Just an observation from what I've gone through on a McQuay unit I've worked on.

And yes! I too think the compressor is toast. You may keep it running for a short while, but it's on it's way out.

Sorry!

[AiResearch]

Hate to say it but it sounds like a rushed through installation. One where all of the parameters were not looked at. And I can't blame the contractor 100%. Few want to pay for a job done right.

Large split systems like this require much thought and consideration on the application and installation if they are to succeed and live long. Especially with a refrigerant retrofit.

[acguy951]

Been there, done that......
If and when you change the compressor don't be surprised if they recommend and send you a pipe changing kit. The two compressors are in parallel correct? If so, they may possibly have you change the oil pipe connection from where it may be, high on the compressors and they may have you put caps on those ports, take out the sight glass on the compressor and put a new line lower, screwed in at the old sight glass threads.

I may be completely off the mark here.
But if they do indeed have you do that, in my little mind it tells me that they know they had a design problem and the oil wasn't getting to each compressor evenly and the one suffered to the point that it messed up the bearings to the point that you are at now.

Just an observation from what I've gone through on a McQuay unit I've worked on.

And yes! I too think the compressor is toast. You may keep it running for a short while, but it's on it's way out.

Sorry!

Mrak: We got the oil analysis back indicating minimal moisture, high acid, high aluminum high iron and silicon. Mcquay just sent us 2 more compressors. Had a quality assurance guy come out from Mcquay to look over the job for a second time. Took refrigerant line sizes and lengths, pics etc. They now want a sequence of operation report. Unsure what the outcome is going to be on this. We arent installing the new compressors until we get feedback from Mcquay. Also fyi, the second circuit of tandem compressors is piped exactly the same as the first circuit, same refrigerant charge amount, same everything! No problems on that circuit. When we do replace these compressors we intend on doing multiple oil changes, installing removable core filter driers and installing some other type of controls possibly. We did look at the oil line and were thinking the samething about that. Well have to wait and see.

[acguy951]

Been there, done that......
If and when you change the compressor don't be surprised if they recommend and send you a pipe changing kit. The two compressors are in parallel correct? If so, they may possibly have you change the oil pipe connection from where it may be, high on the compressors and they may have you put caps on those ports, take out the sight glass on the compressor and put a new line lower, screwed in at the old sight glass threads.

I may be completely off the mark here.
But if they do indeed have you do that, in my little mind it tells me that they know they had a design problem and the oil wasn't getting to each compressor evenly and the one suffered to the point that it messed up the bearings to the point that you are at now.

Just an observation from what I've gone through on a McQuay unit I've worked on.

And yes! I too think the compressor is toast. You may keep it running for a short while, but it's on it's way out.

Sorry!

Mrak, tell me some more about your particular experience with the Mcquay unit you referred to?