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View Full Version : Doh!!!! Another one bites the dust!



herefishy
18-09-2003, 06:48 PM
A few months ago I performed a compressor change-out on a minus20F storage. The compressor had spun a bearing. Looking for possible causes -

Compressor contactor lock-out timer set for 5 minutes after thermostat calls (or defrost termination :eek: )... I got rid of that.

Faulty fan delay/defrost terminate... I Replaced that.


Now the replacement compressor is locked rotor. :confused:


My tech comes back to the shop to change-out recovery bottles and I tell him to tip the compressor (hermetic) and measure the oil charge that comes from the crankcase to determine if the previous compressor had left its charge in the system to overfill the new crankcase.

He pours 3oz of oil out. :eek:

Thinking about it a bit, I consider that the oil must be in the accumulator. The particular accumulator has a threaded port in order to accomodate inspection, according to one man on the job, so I instruct to inspect.

"We've struck a gusher", he reported, relating to his past oilfield experiences. :rolleyes:


I assume that the oil-pickup facility in the accumulator is plugged or otherwise "not conducive to proper oil return". It is now going to be replaced.

This is the first time that I have experienced this phenomenon (in 22 years). Did I not properly service this system with a mechanical compressor failure?

My understanding is that a burn out is best addressed by replacement of any accumulator in the system, but should I have changed out the accumulator during the process of the initial compressor change-out, as a matter of course?

Dan
19-09-2003, 12:57 AM
That's a tough question. I wouldn't normaly change out an accumulator after a compressor failure. When you are working on small units, even a compressor change gets close to the cost of condensing unit replacement. More than likely the clogged accumulator was the reason for the first failure.

You got snake bit. Let's face it, a service call begins with some sort mistake that affected the machinery.

I think it is not asking too much for a service tech to be permitted to make a mistake before he makes proper repair.

There's a point where practical economics dictates that we do not do a completely thorough job of analysis.

Me, I would be thinking, this thing has a filter drier on it, why suspect the accumulator? As you say, this isn't a common occurance.

When we diagnose a failed compressor on a warrantied True glass door freezer, they just send us a replacement condensing unit.

It makes a lot of sense to me, in the long run.

herefishy
19-09-2003, 01:53 AM
Originally posted by Dan
I wouldn't normally change out an accumulator after a compressor failure.... (but).... More than likely the (problematic) accumulator was the reason for the first failure.

Precisely! I know that, now. There was enough that was screwed up in control side of the sytem however, that I did not pursue it any further than the obvious (but in hindsight, the discrepancies would rather be indicative of valve failure (efficiency), rather than (bearing) failure :eek: ). Thank you! :)


You got snake bit. Let's face it, a service call begins with some sort mistake that affected the machinery.

Yeah, I diligently searched for the causes, and addressed several issues... I consider a compressor failure a "symptom" of the problem. Are you implying that you would waranty the replacement?... I'm sincerely asking for advice here, on a "customer relations" type scenario... :)

My vendor has suggested that I attempt to claim compressor warranty (even by putting oil back into the compressor), but I feel self-conscious about that... maybe I should take it on the chin. I know what killed it, and it wasn't any discrepancy by the mfgr of the compressor. Though I think a lot of shops would have never even discovered the cause (after four compressor replacements)!!!!!!! Then the CU would've been replaced, and the problem over (because the effected accumulator is gone! LOL!!!)


As you say, this isn't a common occurance.

Well, thanks for the compliment, but I wasn't sure (if the occurence was uncommon) when I first posted. I feel better since you think it's unusual.... and honestly, I feel really good that I thought to consider the cause of the failure in the first place!!! ;) I was sitting at the desk contemplating the scenario (with my men in the field) when the thought struck me (re: the accumulator) :D I was persnally on the job during the initial failure, and I knew the job!



Thanks for the response. I feel better.....

Would you (try to) bill this out?.... or eat it?

Argus
19-09-2003, 09:40 AM
No, as far as I can see it is not customary to change an accumulator after a burn out, unless there is an obvious problem
I suspect you have bought this one it's difficult explaining to the customer that we overlooked something however unlikely.....

But it reminds me of an experience some years ago on an air conditioning split system.

In this instance it was the usual scenario ? the serial death of several hermetic compressors and as the manufacturers we were called to site to enjoy the usual castigation party.

Eventually, we couldn?t explain it and did the decent thing. We replaced the entire outdoor unit, gratis (far cheaper than throwing good money after bad with further repairs).

I decided after this that I need some parts to cut up for training exhibits and raided the old unit for bits. I wanted amongst other things the accumulator, particularly as most technicians I came across had a sketchy idea of what was inside it.

And that was when the penny dropped.

The accumulator was crammed with oil, and when cut through the middle we saw that it was piped in back to front. Oil could never get out until it reached the top of the vessel to what should be the entry port. All was clear. Further the original manufacturer of the thing had labelled the pipes in reverse. "In" was out and "out" was in....

Ho Hum. That's the joy of refrigeration always something you never thought of.
________
Kawasaki ZG1000 (http://www.cyclechaos.com/wiki/Kawasaki_ZG1000)

RogGoetsch
20-09-2003, 01:11 AM
This is a good one. I've never seen it either and am wondering what was plugging the oil return hole in the accumulator return bend. Could it have been copper oxides or other installation detritus?

I am fanatical about nitrogen purging during installation and will put in a suction filter if I sub out the piping or if any of the equipment is suspect. But I've put them downstream of the accumulator before. . . . something I won't do after reading this thread!

I always measure the oil left after a hermetic compressor change because it has to be removed in order to dispose of the compressor in California, but in a low temp, I would normally assume it to be in the evaporator. What made you think of the accumulator?

Dan
20-09-2003, 03:09 AM
Would you (try to) bill this out?.... or eat it?

Yes. Recall my comments how we are only called when something has a mistake? But I would be gentle and just try to recover my cost. If, on the other hand, you had been the contractor who went through 4 compressors, I would write it off without hesitation. But I would make a bit of a show to the customer regarding my generosity and honesty as I pummelled my technicians during our next get-together.


Yeah, I diligently searched for the causes, and addressed several issues... I consider a compressor failure a "symptom" of the problem. Are you implying that you would waranty the replacement?... I'm sincerely asking for advice here, on a "customer relations" type scenario...

I think I responded to this in the paragraph above, but if you are referring to my mention of the True Corp just sending us a condensing unit when we condemned a compressor, they are likely providing good service to themselves, the customer, and the contractor. They make the repair in the factory at greatly reduced pricing and without worry of anomalies such as a clogged orifice somewhere.

As far as customer relationships scenarios go, you either choose to look at history or into the future and you make your decisions irrespective of warranty issues. It's never that simple of course, but a manner to think about whether you want to keep or lose a customer.




The accumulator was crammed with oil, and when cut through the middle we saw that it was piped in back to front.

Now that is something I more often see than a clogged return! It's good practice to look for the "inlet" and "outlet" or little arrows on directional devices such as check valves and accumulators when one can.

Sort of like checking the positive and negative on DC devices.

Fixing things implies there is a mistake.

"For gosh sake, Mr. customer, do I, the person who finally fixes it have to bear the entire burden of the mistakes I repaired, even if I missed some along the way?"

I then tell the customer, "I will do whatever you think is fair"... to a customer I want to retain... but which is most of them. Then I take my licks.

I am a true believer that a trusting relationship between a customer and ourselves, the contractors, can achieve good balance regardless of our mutual mistakes.

Dan
20-09-2003, 03:16 AM
But I've put them downstream of the accumulator before. . . . something I won't do after reading this thread!

I don't think so. I think the suction filter should be as close to the compressor as possible. It is the last chance, so to speak.

What if the residue that clogged the oil return was stirred up rust from the day it was installed? I think you should stick with the way you do things. A clogged oil return in an accumulator is a rare exception in my observations.

Gary
20-09-2003, 08:10 AM
That's an excellent and very difficult call, herefishy. I'm impressed. :D

herefishy
20-09-2003, 05:00 PM
Originally posted by RogGoetsch
I've never seen it either and am wondering what was plugging the oil return hole in the accumulator return bend. Could it have been copper oxides or other installation detritus?


I (personally) completed the repair yesterday evening. I have the accumulator in possesion, and will cut it open and explore. the lubricant in the system is prestine, a lovely clear unclouded translucenecy.


What made you think of the accumulator?

We scrubbed over the system upon the first visit (compressor change-out). Checked/corrrected superheat, repaired/corrected control circuitry... the thing was running like a champ. Of course Upon the (second) failure I had the feeling (knew) that this failure was lubricant related (even though I originally thought that the compressor was full of oil... and I didn't consider it possible that the lube would be left in the evap, because the velocities (capacity) were correct. This system has been in service for 4.95 years.

There has been a lot of discussion on this forumn regarding accumulator application, and I have paid a lot of attention to it. I guess the accumulator was something that I just didn't overlook. :) ... otherwise, I dunno :p

.... isn't it best that the accumulator be capable of containing the entire system oil charge of the compressor? LOL!!! .. just kidding. :p

Dan
21-09-2003, 03:19 AM
There has been a lot of discussion on this forumn regarding accumulator application, and I have paid a lot of attention to it. I guess the accumulator was something that I just didn't overlook. ... otherwise, I dunno

LOL! But there is an element of truth. Every bulge we build into a system affects another unbulged part. A receiver is a bulge in the liquid line, for example, but it begets storage somewhere else.. maybe in a condenser or evaporator.

Bulges and traps. The bane of our trade. Our band-aids. Our necessary band-aids, nonetheless.

I go along with Gary. Good thinking.

Dan
21-09-2003, 03:41 AM
There has been a lot of discussion on this forumn regarding accumulator application, and I have paid a lot of attention to it. I guess the accumulator was something that I just didn't overlook. ... otherwise, I dunno

LOL! But there is an element of truth. Every bulge we build into a system affects another unbulged part. A receiver is a bulge in the liquid line, for example, but it begets storage somewhere else.. maybe in a condenser or evaporator, or in the piping.

When you are done with this job, could you share how much it cost you compared to a condensing unit replacement?

herefishy
21-09-2003, 05:28 AM
The first compressor was covered under the mfgr (KeepRite) 5-year compressor warranty (gee, I hope they pay me for the replacement :p I've never done a claim with them)

the customer was charged about $1,200.00 for the (warranty) compressor replacement (rooftop), wiring/control remediation, defrost terminate/fan delay replacement, and a fresh R-404A refrigerant charge, filter-drier, yada, yada. This included emergency service, weekend rates for troubleshooting (1-1/2x labor), and essentially two visitis on that Saturday, because when I first visited, the circuit breaker was tripped, and when reset, the unit ran fine (we had an electrical storm the night before).

But the electronic freezer thermometer/alarm was malfunctioning and started beeping, and the store mgr called me back. When I re-arrived, I noticed the evap fans had stopped (no one else noticed). The breaker was tripped again, but when I reset it the second time, the compressor didn't sound so good. :(

The CU is a 3hp hermetic outdoor unit - low temp. I guess a complete CU change out would run about $4,000.00?


This second visit, we had gotten down to the accumulator problem within two hours of arrival. I spent 4-hours on performing the (second) change out including the accumulator replacement.

Argus
21-09-2003, 12:18 PM
Be interesting to hear what you find in that old slop pot, HF!

Remember, my dodgy accumulator all those years ago had been installed the 'right' way when they built the unit.... it's just that the original manufacurer put the wrong labels on the wrong pipes so that 'in' and 'out' were reversed. I hope you didn't get the other one!

It strikes me that if the draw hole at the base of the return tube is blocked, it will still return everything in the pot in the neat state when the contained level reaches the top of the return pipe, about halfway up the vessel as a rule. In that case you will probably get liquid carry-over, which may explain you bearing damage.

Sealed compressors and other items are a terrific idea, but aren't they a pain when you want to check what's going on without destructive surgery?

Ho Hum. There's an interesting thread in the offing about the most unusual cause of compressor death in a system - there must be some great stories out there.
________
BMW 132 (http://www.bmw-tech.org/wiki/BMW_132)

Dan
21-09-2003, 10:37 PM
Keep Rite are pretty good people to work with. Sounds like you provided some great service with fair pricing. Good Job, there, HF.

herefishy
24-09-2003, 10:34 PM
We opened up the accumulator, today. Couldn't find any discrepancies, however.

herefishy
24-09-2003, 10:39 PM
huh????????

Argus
25-09-2003, 09:25 AM
That Draw hole looks a little small to me HF........ I'm guessing from the scale that it's about 0.25 mm?

Any filters down stream of the slop pot?

Could it have got blocked by thickened oil at low temperature? I suspect that you were evaporating at -30 / -35 or more. (I have to convert to Celsius here!)

I have encountered oils that thicken to the consistency of treacle at low temperature but return to a normal viscosity at ambient temperatures. In the process they will block small orifices, gauze filter etc.

It's a long shot, but if you have a sample of the original oil left, you may consider putting it in a deep freeze overnight to see how low temperature affects the viscosity.
________
one vaporizer (http://www.vaporshop.com/one-vaporizer.html)

herefishy
25-09-2003, 01:37 PM
I had photo problems, yesterday. Here's pic 1 with the screen in place. Yes, the hole is tiny.

herefishy
25-09-2003, 01:41 PM
The first compressor was original, and it had been in commission for almost 5 years. The oil was prestine.

The design SST is -30F.

I am a little disturbed by the condition of the accumumlator. I certainly have not satisfied my curiosity in regard to what really happened. Is that hole supposed to be so tiny? Or was it to be the size of the 3/16" depression that the tiny hole is situated in? Like maybe the hole punch didn't make it all the way through the steel pipe at the bottom of the bend, perhaps?

:confused:

Argus
25-09-2003, 02:38 PM
HF - I did not realise that there was a gauze filter in place.
Superfluous insisde a sealed pot, my opinion, but it must be there for a reason. (If it blocks how are you supposed to clear it)?

Generally being sealed units, accumulators are seldom inspected on the inside, but for what its worth, the few I have seen have all had larger draw holes that that. About 1mm to 1.5 mm diameter seems to be the going rate. Never seen a filter on any of them, just a hole, because you don't need any pressure loss, however small, on what is, in effect, a small venturi.

Going back to my oil theory, we encoutered it on a wire strainer like that one positioned in front of an accumulator inlet pipe, (3/4 pipe as I remember).
It was unusual insofar as the oil thickened up enough to block the filter so that the compressor ran on a 25" vacuum. As soon as the temperature rose, it went nice and thin again.

I guess the kit is OK Now?
________
Nagare (http://www.ford-wiki.com/wiki/Mazda_Nagare)

herefishy
25-09-2003, 11:02 PM
Hi Argus :)

The first replacement took three months, thereabouts, to take a crap. The unit is running fine. Since we have removed the accumulator (that was holding the oil charge of "two" compressors), I assume if there was any discrepancy in the quality of the lubricant (contained in the accumulator), it is gone now.

We'll see.

baker
26-09-2003, 07:39 AM
I don't have my books with me, but I can remember my HVAC school text on accumulators showing a Number 80 drill hole for oil return.