refrigeration techs here?

[rust in the eye]

EDIT: 2/15/23 I had forgotten about this thread I started years ago but now wanted to give closure.
After consulting various service companies that wanted to send their kids to college on my dime I decided to buy the parts and equipment needed to replace the compressor myself. Attempts to braze self piecing fittings failed due to selecting the wrong solder so I put the job off.
Well SHAZAM the damn thing healed itself. All I can figure is that it had shook loose form the internal mounts but had somehow managed to shake itself back into place.
Its been quiet for a long time now.
Man, I hope I didn't just jinx myself.
Read on for the weird temp related behavior if it interests you.

Okay, Here is one that has me stumped.
refrigerator is rattling after completing it's cooling cycle.
The compressor mounts to the fridge chassis are sound, the compressor is banging inside the hermetic can. This only occurs after the compressor turns off, it is silent in operation.
Assuming the compressor has come loose of the internal springs I've looked at new ones and they seem to have the same amount of rattle given a shake.
After removed the cabinets above(built in 'fridge)and the cover over the compressor it does it much more frequently and louder. Covering the works(effectively insulating it)reduces the frequency and vigor with which it shakes. Remove the cover and it bangs like hell again. It's not the cover diminishing the noise, it's diminishing the event.
There are no charge ports to see what the pressures are but I am thinking that perhaps it may simply be low and the ambient temp around the works is effecting things.
I'd love to know the thoughts of any refrigeration techs out there.

 

[Milton Shaw]

The compressor hangs or sits on springs. One of the springs has broken and letting the compressor bang against the case. This will eventually cause the compressor to internally break a line and quit pumping. The noise happens sometimes when they start or cutoff. Plan on having to replace the compressor or refrigerator in the near future. I had to replace my heat pump compressor for the same reason 15 years ago. It made a noise for a couple of weeks and then just about quit pumping.In answer to your question, the ambient temp makes a big difference in the pressures in the system and that makes the compressor work harder and jump more when it switches off/on

 

[rust in the eye]

The compressor hangs or sits on springs. One of the springs has broken and letting the compressor bang against the case. This will eventually cause the compressor to internally break a line and quit pumping. The noise happens sometimes when they start or cutoff. Plan on having to replace the compressor or refrigerator in the near future. I had to replace my heat pump compressor for the same reason 15 years ago. It made a noise for a couple of weeks and then just about quit pumping.

This was also my assumption.
How do you explain the difference when it is kept warm or exposed to ambient temps?
The old compressor has ~ the same wiggle as a new one too?

 

[oldgoaly]

If the internal compressor works loose of it's mountings it will break connections refer or electrical sometime. Just a matter of time.

 

[Full Throttle]

Time bomb

 

[BillK]

My garage fridge which was manufactured in 1951 has done that almost its entire life. I wouldn't know how to act if I didn't hear it every once in a while. My Wife's parents had it when she was a kid and she says it made that noise as long as she can remember

 

[rust in the eye]

Can anyone experienced with refrigeration help me understand why the difference when the compressor area is kept warm? What is actually going on inside a hermetic compressor AFTER it shuts down?
And why does a new compressor seem to have the same amount of jiggle?
I'd rather not replace an engine in order to address the need for a tune up.

 

[oldgoaly]

Kept warm? how warm? The compressor is cooled by the refrigerant gas returning to it. Some a/c compressors use a crankcase heater or a bleeder circuit on the windings to keep the oil warm in case the unit is turned on during cooler/colder time.
Compressors generate heat.

When the compressor stops it's not doing anything, the higher pressure aka condenser to the expansion device (valve or restrictor) will bleed thru the expansion device to equalize the pressure so the compressor will not start under load.

Now some scroll compressor have check valves that make a odd noise when the shut down. Hopefully that answers your question.

Those old 4 pole motor/compressors in older fridges and a/c units do clang some, but they start easier than the 2 pole ones.

 

[rust in the eye]

It's a dramatic difference first noticed when I removed the cabinet above which also served to keep the warmth in. After that was gone the episodes became much more frequent, lasted longer(30 seconds or so)and louder.

I threw a foam cushion on top in an effort to dampen the noise when this occurs and found the knocks less frequent and with less vigor as before the cabinet was removed. It isn't that I'm not hearing it, it's way better when covered.
To answer your question, the bottom of the cushion seems about body temp, perhaps a bit more, not hot by any means. It surely makes a big difference though.
The knocking is absolutely in that equalization phase you mention. I can shut off the power while it's knocking and it will carry on as always.
I'm thinking the compressor knock is a symptom of another issue not THE issue. Just trying to understand how these work.
Can you think of a scenario that would cause this?
It's a typical hermetic fridge compressor(Embraco) on top of a Thermador.
Thanks for your thoughts

 

[oldgoaly]

How old is it? I've heard all kinds of compressor noises, most are signs of a total failure. Worst noise? Stuck a hard start kit on a older window a/c unit. You could hear metal parts being thrown against the outer case. Needless to say it was scrap metal then.

 

[rust in the eye]

How old is it?

2004
cools just fine, just this damn noise.
I'd really like to know what is going on inside that causes this. Compared with a new compressor this one doesn't seem to be any looser.

 

[oldgoaly]

No way to see inside unless you cut the housing open. There are special compressors with sight glasses in the housing for engineering purposes. Many moons ago 1979 -81 my task at Singer climate control division was to find out why the high failure rate in a 2.5 ton heat pump with a Tecumseh ah5529e compressor vs a Copeland and Sunstrand. Basically we over charged the unit with 20+ pounds of R22 and watched the waves of liquid refrigerant flood the compressor. This was done is a test lab in St.Louis which is long gone and a taco bell is in it's place. The only one they had it was special to blow it up! Also those compressors were to specs and verified for testing purposes. I won't get into all the beer we drank.... but they(engineering) bought us more. Ah ya should of seen Rich turn green when they gave him his.... We did figure it out, found the reason "over charged" Then a month or so later taking the heat pump certification class, found out marketing had not gotten the info. They were in the next building so I ended up running the class to show how and why with out the aid of sight glasses but still had the other toys. No computers, the data logger had nixie tubes, hundreds of thermal couples attached to everything, a vibration sensing device. Oh the fun....

 

[American Locomotive]

I really think you're looking too much into the compressor covering making a difference. I'm pretty sure you've convinced yourself it's made a difference more than anything. The compressor gets very little/no cooling from ambient air. It's cooled by the suction gas.

The knocking when coming to a stop comes from the compressor not being able to complete the compression stroke, coming to an abrupt halt, and then shaking around inside the hermetic can. Any hermetic compressor will clunk around a bit if you shake them hard, but if it does it in normal operation the springs inside are worn out/broken.

 

[rust in the eye]

Well, I also wonder if I am overthinking it but can assure you the difference when it is covered is dramatic. No doubt of this. the wife has noticed as well wondering if I had made a fix.
The compressor is NOT running when this occurs. It has shut down, I can disconnect power and it carries on. Uncovered it has done it loudly for 30 seconds or so.
Has to be liquid refrigerant boiling off where or when it is not supposed to.
Can a low charge or other condition contribute to/cause this?

 

[oldgoaly]

If it is the refrigerant boiling off / equalizing 30 seconds is about right. But that noise should be muffled in the low side coil. Now could you have a check valve and a scroll type compressor? you can check the compressor data plate, should say "scroll" on it. But all the check valves noises I have heard last 10-15 seconds at the max.

Generally a soldered system doesn't leak like the older automotive systems which had rubber/vitron compressor seals. A bad solder joint or some wear thru of a line or coil cause major leaks / problems. All these refer units are considered critical charge which means more is not better! Is the condenser fan cooled or hidden inside the case? Fan goes off when compressor or power is off.

 

[TRWham]

Perhaps liquid collecting in the crankcase during the run cycle because of floodback (maybe the evaporator is partially iced) is boiling during off cycle.

 

[rust in the eye]

Perhaps liquid collecting in the crankcase during the run cycle because of floodback (maybe the evaporator is partially iced) is boiling during off cycle.

Which, if so, would indicate that it isn't defrosting properly.
Fortunately we have another fridge so I'll move the food and let this sit off and open all day to defrost if that might be the case.
Will advise.
My compressor;

 

[rust in the eye]

I attempted to braze on a self piercing charge port but failed miserably. See the blobs on the suction line(back) in second photo
I cleaned the line and was using 56% silver brazing wire and MAPP gas. No trouble getting it hot enough to melt but the wire just won't flow into the joint. I'm told flux isn't needed when brazing copper to copper with this wire. What am I doing wrong?

EDIT: I removed the coverings to take the two photos above perhaps 10 minutes ago. The fridge has been quiet all morning until just now another raucous banging rattling event.
Something I've neglected to mention is that regardless if covered or not the events seem to occur when the fridge hasn't been opened for a long time. On a busy weekend cooking day when we are in and out every few minutes(and ostensibly working harder) it is quiet as a mouse.
Just banged again a few times while writing last paragraph

 

[American Locomotive]

A quick google search shows that 56% requires flux and 15% does not. Use 56% when joining dissimilar metals, use 15% when doing copper-copper.

 

[rust in the eye]

A quick google search shows that 56% requires flux and 15% does not. Use 56% when joining dissimilar metals, use 15% when doing copper-copper.

Thanks, I was advised elsewhere to use 56%. Glad I spent the money.
Will the 56% be okay with flux? The white stuff?
Regarding the issue;
Defrosted and no joy. Started knocking like mad during the night once it had fully cooled. I went down stairs and gave it it's blankey and it shut right up.

 

[rust in the eye]

This is nuts.
after the defrosting and getting back to temp it did the usual rattle & bang dance while uncovered.
With it covered it has been quiet since yesterday. The temp settings defaulted to the preset 36* & 0* in the freezer. Can't recall where it was before but I think the fridge was warmer. I just know that if I reinstall the cabinet overhead it will resume.
What the hell is going on here?