Scroll Seizure

[jwasir]

We've supplied a condensing unit with falling film evaporator, year back.

Since then, we've replaced 4 scrolls, 1 after every 3 months.

Comp is copleland ZR-300KC-TWE- 25 HP - 575V.

Tear down report says that oil is diluted, scrolls spun, etc.

After every replacement, the subcooling, superheat, amps draw, discharge temp, etc was checked, they were always in limits.

The compressor oil seems to be black after failure.

The oil seems to be little acidic.

After 1st failure, LL sight glass becomes blackish in colour, which is better now.

The suction and liquid filters were replced after every failure with charcoal and high water capacity cores.

Oil is checked frequently, which at 1 point seems ok but later becomes acidic.

System has HG bypass and pump down option.

Pump down is done down to 15 PSIG.

System pressures are 55/220 PSIG with R-22 refg.

Timer is installed in series with LL soln for 10 mins.

System is indoor, complete with CC heaters.

Sometimes, comp runs for few mins. and stops due to open flow switch.

Besides this, there is another system with same design and running under very similar conditions with bitzer recip.

This is running perfectly since 1 year.

Does the scroll system needs new refrigerant and system flush?

Is too many starts could be problem?

Is shorter running time could be issue?

Still couldn't figure the actual problem!!!

[WINJA]

sounds like liquid flood back , could be due to user error like no evap load etc , have you got an acumulator and oil seperator fitted? you could find out what your lowest running suction preasure is under normal conditions and set the LP cut out just 5 or 10 psi less.
those copeland scrolls are quite reliable

[wambat]

Have you ck all of these conditions;
Compressor oversized for load
The "cycle on" and "cycle off" range of low pressure control is set too close
A leak in liquid line solenoid valve

and with regards to hot gas bypass make sure you have a check valve installed in the evaporator section in the hot gas line before it enters the suction side. This is to prevent the liquid in the bypass “off cycle” from filling the line and slugging the refrigerant lines on bypass/compressor start cycle thus deluting compressor oil

Line sizing should be calculated to not exceed a 6 to 12 psi pressure drop in hot gas line and it should be insulated and with HGBP an accumulator is always a good idea , the kind used with heat pumps are the best

[chemi-cool]

Hi jwasir.
Had a similar problem with laser cooling unit.
I have replaced the HGBP with evaporator pressure regulator and it runs perfect for a few years now.

What controls the condenser fans? Keep the head pressure low [200 psi] to prevent the refrigerant from getting too hot.

Did you find any traces of water in the oil?

If your timer is set for 10 min, after the LSV was activated, you are risking the compressor with liquid flood back.

I would change the control so the temp controller will activate the LSV and not the compressor and let the compressor start when pressure rises.
Scrolls don't have problems frequent starts.

[jwasir]

We have temp sensors in the suction line, which stops the comp, if superheat goes below 10F.

The timer energizes the valve and not the compr.

No traces of moisture in the system.

The check valve has been installed in the HGBP line.

Huge accumulator is there, which can hold 60-70% of the evap volume.

Any other comments!

[jwasir]

Hi All,

I Am Still Looking For More Views, Please.

Need To Resolve This Time!!

[SteinarN]

How is your hot gas by pass system operating? Where is the hot gas by pass line conected to the suction line?
What are the suction and discharge pressure and the suction and discharge temp when the hot gas by pass is activated?
How long is the hot gas by pass activated?

Personally I dont like hot gas by pass the least due to low system efficiency and potential problems with high discharge.

[majo]

couldn't the oil be flushed away because of high bypass flow? Had this once because pressure regulator was set too high en flushed the oil out of the sump every time.

[jwasir]

SteinarN,

Hot Gas is dumped in the evap thru the side port.

Hot Gas is always activated with bypass valve, when comp is running.

The Superheat at the comp is 17-20F.

The pressures with HG on is 52/210 PSI with R-22.

How can we check if too much HG is bypassed, when superheat is normal?

As mentioned, there is another system next to this running with exact conditions and never had problem. The only diff. is that other system has Bitzer recip comp.

[nike123]

Tear down report says that oil is diluted, scrolls spun, etc.


The compressor oil seems to be black after failure.

The oil seems to be little acidic.

After 1st failure, LL sight glass becomes blackish in colour, which is better now.

The suction and liquid filters were replced after every failure with charcoal and high water capacity cores.

Oil is checked frequently, which at 1 point seems ok but later becomes acidic.


Does the scroll system needs new refrigerant and system flush?




From above i presume that first compressor motor was burnt because of mechanical failure of scrolls. Is that correct?

Second, you asking here " does the scroll system needs new refrigerant". Does that mean that after first compressor burn out you recovered and then returned same refrigerant?

[mickay]

Hi
Re scroll problems i notice the comp stops on flow switch does this mean at times there is no evap load?
Also i notice the l.p set at 15psi this could be set at 50psi or a touch lower
I have seen many a time l.p. on scrolls/rotarys set too low and no cooling coming back [short of gas ,t/x prob etc] and comps failing.Aiso a start to start timer on comp.Every 3 mths could be running short of gas but you are not going to be there 24/7 watching it so you wont know about a prob if the l.p is set to 15 psi by then the damage is done. The prob could be some thing completely different but this l.p.setting prob is something i have come across before as mentioned.The scrolls need heaps of cooling.

[jwasir]

From above i presume that first compressor motor was burnt because of mechanical failure of scrolls. Is that correct?

Comp's were never burnt but always got seized.

Their is contamination in the system due to carbon in the pipelines, while brazing w/o nitrogen.


Re scroll problems i notice the comp stops on flow switch does this mean at times there is no evap load?

Flow switch opens, when there is no flow over the evap.

There are instances, when load is low on the evap thats why HG by-pass is incorporated in the system.

The cut out pr is set to 15 PSI for pump down...

If set higher, there will be short cycling of the comp.

Will discharge line temp cut out control the low cooling of the comp??

[jwasir]

Any more feedbacks???

[nike123]

Lowest pump down pressure setting for Danfoss Performer scroll (R22) is 19 PSIG (33,7 PSI absolute). I don't know what is for Copeland, but I presume that is simmilar.

What is your total system charge?
Do you have liquid receiver?
What is temperature of suction gas when HGBP is active?



Sometimes, comp runs for few mins. and stops due to open flow switch.


I don't understand about what switch you are talking here. Does that switch is on secondary side of evaporator?



Besides this, there is another system with same design and running under very similar conditions with bitzer recip.


Bitzer semi-hermetics are very good in handling heat rejection (their motors are usually over sized in comparison with others and don't generate that much heat ) and that could indicate that you have problem with scroll compressor overheating in some points of operation. That also indicate black oil and gradual acid rise in oil.

You should closely monitor discharge temperatures and find when are they much higher than in normal operating conditions.

[jwasir]

What is your total system charge?
Do you have liquid receiver?
What is temperature of suction gas when HGBP is active?

System charge -- 250 lbs because of flooded condenser (Winter Charge)

YES-- There is receiver.

Superheat is 18F with HGBP active.


I don't understand about what switch you are talking here. Does that switch is on secondary side of evaporator?

This is the flow switch in evap, which opens during no flow.

[nike123]

Do you have in hand diagram of refrigerant circuit? Could you post it here?

[wambat]

Please ck your installation against this and see if there's something you can improve on
http://www.trane.com/commercial/library/vol32_2/adm_apn007_en_0503.pdf

[Fri3Oil System]

if the oil was black you were having acidity. The first part of your solution should be to clean properly the system.
I have tried, without success to insert here some pictures of a cleaning we did in the island of Jersey, UK, on a Carrier ductec system which had 2 burn outs in a few months before we cleaned it. This was 2 yrs ago now, and no probs since we did our job there. By the way, they are using still the same refrigerant, as we recycled it.

[hillbillywillie]

did you use high acid driers after each burn out?
Black oil could suggest extreme heating of oil-are the oil filters clean and allowing good oil flow?
Acid in the oil will burn winding insulation and eventually cause a failure in windings.
black oil could contain sludge, which would block pick up filters etc.
is the correct oil in the system, or could there have been cross contamination with a different non compatible oil?
check suction filters regularly as they'll cause problems if the flow is restricted.

[jwasir]

Yes, we used acid filter after each burn out. The filters were black at every change. After 5-6 changes, filters were pretty clean. Oil is Mineral oil, compatible with R-22.


did you use high acid driers after each burn out?
Black oil could suggest extreme heating of oil-are the oil filters clean and allowing good oil flow?
Acid in the oil will burn winding insulation and eventually cause a failure in windings.
black oil could contain sludge, which would block pick up filters etc.
is the correct oil in the system, or could there have been cross contamination with a different non compatible oil?
check suction filters regularly as they'll cause problems if the flow is restricted.

[Magoo]

You could still be getting acid build in system after multi drier core changes, Can you do an oil analysis, I am thinking that problem starts at HG defrost that fills evap with liquid. Then floods back, your suction accumulator should be able contain 80% of system charge safely. So with 250 system charge you need a huge accumulator. Concider revamping the hot gas defrost as per earlier posts.

[jwasir]

It is HG Bypass and not defrost. We have huge accumulator in the system, which can take 100% evap charge.

[sendhilkmar]

If it is a repeated failure then I guess it is related to system processing. At times slow vapor charging results in scroll failure after 3 to 4 months.

[shafaqat ali]

Dear jawasir
you must clean your system Dry nitrogen+R11 after you dont face the same problum .
goodluck