Making the best of the worst...

Okay, looking for any insight that maybe I've overlooked here.

Customer had compressor (Copeland 9RS1-1505-THC) compressor that started to trip the oil pressure safety. Through troubleshooting, found TXV's were at fault, and were replaced (both of them on both evaporators). Superheats were normal, but compressor had be subjected to much flooding overtime. You could hear lower end problems, and recommended replacement of the compressor.

Customer then found a used compressor at another jobsite, that HE opted to have installed instead of new compressor. The original compressor that was removed had a serial number from 1990. This compressor found on another site had a 1983 serial number. (A step in the right direction, eh?)

Installed this replacement compressor. Oil pressure much better, no lower end noise from it. After startup, saw that the oil in the site glass was low. I said, I would have to return on Monday, would fill up then. (did not have any on the truck right then).

Over the weekend, this compressor tripped the oil safety. I thought, could be expected, since oil level was low. Added oil, on Monday. Ran great.... until

Friday morning, got the phone call again, tripped oil safety AGAIN. Customer had reset, and was running upon arrival. Pumped system down (shut off solenoid) Oil level went high on the site glass. Restarted, ran for a while, pumped down again. Oil level finished BELOW the site glass. Every pump down, the oil level was at a totally different level everytime.

Flo-Con head pressure regulator not working, and maintaining head pressure properly. It has a working crankcase heater (newly installed). Also has an oversized liquid line. (+20°F evaporator) which is 1 1/8". It appears for this line set run, it should only be about 5/8".

It appears that the compressor is passing a lot of oil into the system through worn piston rings and blow by. So, here's the question(s)....

1).Could the oversized liquid line be playing a part in not allowing the oil to consistantly return to the sump of the compressor?

2).Could the head pressure regulating valve not working properly also have that significant impact on the oil return?

The real answer I know is the compressor should be replaced with a new one that would not have this type of problem. But I'm just checking the "what if" department since the customer doesn't seem to want to spend any more money on this project.

I don't think you don't need to look any further than the piston seals. Everything else is a fine tuning.

i have had this years ago when the compressor was too small sat on a large system,it cant move the gas round the system fast enough and the oil ends up sitting in the evaporator,sounds like the liquid line pipwork should be the suction !,those semi,s do chuck oil about when getting on a bit but assuming you have a seperator that works with a sight glass in to see it returning it should settle out,other thing is run it on a synthetic oil if its not allready on it,that may help,good luck.

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Originally Posted by old gas bottle

i have had this years ago when the compressor was too small sat on a large system,it cant move the gas round the system fast enough and the oil ends up sitting in the evaporator,sounds like the liquid line pipwork should be the suction !,those semi,s do chuck oil about when getting on a bit but assuming you have a seperator that works with a sight glass in to see it returning it should settle out,other thing is run it on a synthetic oil if its not allready on it,that may help,good luck.

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Please take note of the above.

1/ has the system got an oil separator:confused:

2/ If not the liquid line is acting as one

Even with an oil sep, the oil can still have problems comming back in an instance such as this.

Junk is junk, I will work at most systems, but if the customer is not listening, either make him listen or cut your losses, he will blame you for the problems, not himself when it all goes pear shape;)

Kind Regards and good luck, Andy:)

Thanks all for your input.

No oil seperator on this hunk of junk. One of the other service techs had offered that as an idea, but the cost involved in putting that on just to keep an old compressor running, just isn't cost effective.

The customer of course isn't happy, but HE choose to install an old compressor, so tough luck on him. I came into the middle of this project. I don't have any hard feelings if this guy is not happy, because he has dug his own hole.

I was just wondering here if there was any other remedy being over looked before informing him that his idea was a bad idea.

Who ever said that the customer was always right, was dead wrong.

Over sized liquid line shouldnt realy affect your oil return, although an incorect suction line size will, Just one question is the gas charge Ok I have come across systems especaily semi hemetic condensing units where they start to go short of gas not enough initailly to cuase temperature problems but enough to effect the gas velocity in the suction line & cuase intemitant oil trips?

got to say that a liquid line twice the size of what it should be will throw all sorts of problems up, oil being one of them,theres bound to be a pressure drop leaving the reciever entering a much larger bore pipe and oil will be slow to move through and be laying arround and upto the valves,also slow to get through the coils,maybe thats why its getting a bit back when being pumped down.

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1).Could the oversized liquid line be playing a part in not allowing the oil to consistantly return to the sump of the compressor?

2).Could the head pressure regulating valve not working properly also have that significant impact on the oil return?

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Yes and Yes. The liquid line is so massively oversized that it is a likely culprit simply because it can trap a lot of oil. I would change that to a reasonable size. You never mentioned the refrigerant or the location of the liquid line solenoid valve, but I will assume R22 and the solenoid at the refrigerated fixture.

You also never described how the head pressure regulating valve is not working properly. I will assume, since you said "Flo-con" that it is a two-valve system with an A7or 8 upstream pressure regulating valve and an A9 receiver pressure downstream regulating valve.

Without bothering with those details, you could well have oil trapping in the suction line if your discharge pressure is permitted to be so low that you starve the evaporator and lose suction line velocity.

I wouldn't be too quick to recommend a new compressor until I have thought through all the other possible issues.

Were I in your postion, I would take simultaneous amp, suction, and discharge pressure readings and look up the compressor curve with Copeland software such as Cp calc. If you are within 5 or even 10% of the curve, I would take advantage of using the old compressor to fix the things that you suspect are being problematical... for example, running a 5/8 OD liquid line and rebuilding or re-adjusting the Discharge pressure regulating valves. You could advise your customer that his compressor is 8% inefficient but you will try to nurse it along.

If nothing else, when you DO propose a change, include system repairs such as a new liquid line and analysis plus repair of the discharge pressure control valves.

The last thing you need is to put a brand new compressor in and subject it to systemic conditions that caused previous compressor failures.

These compressors have certainly seen their service life. The way the system was installed certainly is not helping the situation at all with the oversized liquid lines.

The piping is 13ft horiz.->6ft lift->13 ft horz ->Solenoid valve-> T (7/8x7/8) [20ft to second evaporator] Each evaporator is reduced from the 7/8 to 5/8 inlet of the TXV.

The customer asked "why do I have another system just like this one on the other side of the building and it's not having this problem." To which I answered "that is a newer compressor (1998) which has has slightly tighter tolerances and is not pumping oil out into your system as quickly as this/these older compressors have been."

The overall system design doesn't appear to be a setup for a compressor failure, but certainly offers no fudge factor for an older compressor slobbering oil all through out the system. At least that is my take on this...

Back for more information: R22 refrigerant. 1 Flo-Con A8 is the only information that is ledgable on the valve. Two check valves are used in the system, and it appears that once a pressure differential is established, one or the other check valve (based on pressure drop) will allow it to devert hot gas to the receiver, or to the condenser. The Manufacturer is Kramer-Trenton.

Personally I would not get too excited about the over sized liquid line.

I think your problem lies within the compressor or system.

First thing I would check is if the compressor can pump down into a vacuum quickly by closing the suction valve.

If the compressor will pull down reasonably well in say 30 seconds, shut the compressor off. If the suction pressure does not rise quickly, then the valves are probably OK.

The piston rings sound like the problem. If the rings are loose the oil will blow right past them into the discharge line.

Here is some information that may help you.

http://66.28.63.222/documents/Kramer_System_IOM.pdf

love how dan descibes it, SLOBERING, must remember that,thought it just applied to me when i see a nice curry!! got to say though,most semi,s when older or even rebuilds chuck oil about the system, either the pipework has to be right or a seperator and enough oil in the system,it allways said, check oil level after running for a period !

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If the rings are loose the oil will blow right past them into the discharge line.

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I think I have asked this on another thread, but I don't recall a satisfactory answer. How does oil blow from a low pressure into a higher pressure?

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Personally I would not get too excited about the over sized liquid line.

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Perhaps. But I like to remove all anomolies. I am trying to remember... is R22 less dense than mineral oil? Could the oil be lying there in a liquid line that moves like a slow stream because it is so oversized?

On the other hand, if the liquid line is so massively oversized, is it possible that the suction line is too?

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The customer asked "why do I have another system just like this one on the other side of the building and it's not having this problem."

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This is a wonderful question. I would take a very close look at the system that is just like this one. Maybe the lines are sized differently, or there is another difference.

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love how dan descibes it, SLOBERING

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I like it too, OGB. But KNKREB deserves credit for the "Slobber" allusion.:)

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How does oil blow from a low pressure into a higher pressure?

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When the piston starts down on the suction stroke, the residual high pressure gas (in the cylinder) expands and it's pressure is reduced. No vapor from the suction line can enter the cylinder until the pressure in the cylinder has been reduced below the suction line pressure.

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Above is an excerpt from Copeland Volume 2.

If the rings are not sealing properly, the oil gets sucked up into the cylinder. When compression starts, the oil is pumped from the cylinder.

Oil carryover may also be precipitated by high oil levels, excessive suction superheat, or oil that is too hot.

Problem: Excessive lubricant consumption
Possible Cause

1. Piston rings damaged or worn (broken, rough, scratched, excessive end gap or side clearance).

2. Piston rings not seated, stuck in grooves, or end gaps not staggered - Clean and adjust piston rings. Replace as required.

3. Cylinder scratched, worn or scored - Repair or replace as required.

4. Piston scratched, worn or scored - Repair or replace as required.

Problem: Oil in discharge gas
Possible Cause:

1. Clogged or dirty inlet and/or discharge filter - replace filter element

2. Oil viscosity too low - Drain existing lubricant from frame. Refill with proper
lubricant.

3. Oil level too high - Drain lubricant from frame to proper level.

4. Detergent type lubricant being used - Drain existing lubricant from frame. Refill with
specified lubricant.

5. Piston rings damaged or worn (broken, rough, scratched, excessive end gap or side
{clearance) - Replace piston rings.

6. Piston rings not seated, stuck in grooves, or end gaps not staggered. - Clean and adjust
piston rings. Replace as required.

7. Cylinder scratched, worn or scored. - Replace or repair as required.

8. Piston scratched, worn or scored. - Repair or replace as required.

Problem: Abnormal piston, ring and cylinder wear.
Possible Cause

1. Clogged or dirty inlet and/or discharge filter - replace filter element.

2. Oil viscosity too low - Drain existing lubricant from frame. Refill with proper lubricant

3. Oil viscosity too high - Drain existing lubricant from frame. Refill with proper lubricant.

4. Oil level too low - Add lubricant to frame to bring level up to an acceptable point.

5. Detergent type lubricant being used - Drain existing lubricant from frame. Refill with specified lubricant.

6. Extremely wet gas - Install dryer.

Above remarks from: http://www.mckenziecorp.com/compressor_guide.htm