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Modified compressor.

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james_s:

--- Quote from: davelectronic on March 26, 2021, 01:51:25 pm ---Yes I have thought about the troubles I could be getting into by opening these compressors up. I'm going to use a water trap to avoid any contaminants in the air supply. It was only for checking oil anyway, I guess I'd see if any oil accumulated in the water trap and access if it needed a top up. I have tried to find the oil quantity these compressors take, but it appears the lubricant is integrated with the refrigerant. The closest thing I could find was a Bambi compressor video showing the guy using 500 ml of oil in the new unit he'd just received. The compressors I have are about 2/3 the size of the Bambi compressor the guy is filling in the video. And I only need to add oil, as they came with about 50 ml oil in each compressor. I'm sure that can't be enough oil, I'm guessing a ball park figure of 250 ml oil for each compressor. I might have that wrong, I guess it's to much if it starts spitting oil out. Tried to think of a way to calculate the oil quantity needed, but it's not easy because of the shape of the housing. I would prefer not to open them up. For filling port, yes I could use the suction entry tube. But an oil site glass would be good. I have reservations on drilling where I can't se what's behind it. Although my drill control skills a excellent, so I could just break through with out the drill bit going to far. I had planned a friend to hold a vacuum cleaner nozzle close to the drilling site, I could at least minimise any swarf getting inside the compressor. I can see on the Bambi compressors, they have a U shaped oval clamp around what I expect is two flanges, one on each section, and removable for servicing purposes. Think I've orded the correct oil, probably have to guesstimate the quantity needed.

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If you can find a datasheet for the compressor it should tell you how much oil and what type it's meant to use. In this application the type doesn't really matter though, and the quantity is not too hard to guess, you want around 1.5" of oil in the sump though a bit more shouldn't hurt anything. The compressor head is at the top and there is a spiral groove in the shaft that pumps oil up from the sump and sprays it out from the top as the shaft spins. Excess oil will cause drag on the rotor but even that shouldn't really hurt anything.

davelectronic:
It was many years ago now, but I did open one up out of curiosity. I found the oil pick up screw at the bottom of the shaft, one thing that puzzled me was how clean the oil was. As it was a fridge I had used for over 10 years, it hadn't broken down, I just upgraded it. So surplus fridge, I investigated the compressor. There is a component in addition to the relay in the two units I currently have. It's about an inch in diameter with two leads attached to it, it doesn't come in contact with the compressor shell at all, but sits above and to the left of the starting relay. No idea what that is, there is a start / run capacitor, but I can't see a PTC anywhere. I've tried frequent start stop cycles and it restarts fine.

amyk:

--- Quote from: davelectronic on March 27, 2021, 11:06:11 am ---It was many years ago now, but I did open one up out of curiosity. I found the oil pick up screw at the bottom of the shaft, one thing that puzzled me was how clean the oil was.
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That's what you get with a hermetically sealed system. Unless the motor burnt out, there's essentially zero wear and the parts can look like new after several decades.

User davida1hiwaaynet on YouTube has a series of videos on rebuilding a fridge compressor from 1937, whose only problem was leaking terminals:


--- Code: ---[url]https://www.youtube.com/watch?v=v0MLNuOF0Ds[/url]

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(I put the URL without embed so you can click through to the other parts.)


--- Quote from: davelectronic on March 27, 2021, 11:06:11 am ---There is a component in addition to the relay in the two units I currently have. It's about an inch in diameter with two leads attached to it, it doesn't come in contact with the compressor shell at all, but sits above and to the left of the starting relay.
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That might be the overload protector. Post pictures if you want an identification.

davelectronic:
Yes interesting, when you think of a piston engine it's oil change always shows wear. Even other types of oil case crankshaft piston compressors show some oil wear going on during oil change. Yet these hematically sealed piston compressors show virtually no wear after decades. I'm not sure how or why, oil properties have excellent coating and surface film abilities... Or the materials, cylinder piston and all moving parts have some super wear protection properties, who knows. I will take a picture of this cylindrical two lead small devise that's mounted to the left of the starting relay.

james_s:

--- Quote from: davelectronic on March 28, 2021, 12:31:46 pm ---Yes interesting, when you think of a piston engine it's oil change always shows wear. Even other types of oil case crankshaft piston compressors show some oil wear going on during oil change. Yet these hematically sealed piston compressors show virtually no wear after decades. I'm not sure how or why, oil properties have excellent coating and surface film abilities... Or the materials, cylinder piston and all moving parts have some super wear protection properties, who knows. I will take a picture of this cylindrical two lead small devise that's mounted to the left of the starting relay.

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I've opened up several different refrigeration compressors, and aside from the two that had burned out they looked like new inside. I think it's largely because unlike an engine, there is no combustion going on to dirty up the oil, and unlike both engines and air compressors there is no ambient air with all of the various dirt and pollution it carries into the system. Also the oil circulates through the system as it is carried by the refrigerant and typically there is a filter, while most air compressors don't have any kind of oil filtration. The parts can also be more thoroughly oiled because the entire assembly is being constantly doused in oil and it is circulating through the compressor too, you can't do that with an engine or a standard air compressor or you'd be losing massive amounts of oil out the exhaust. It all adds up to a machine that can reliably run many tens of thousands of hours. Compressor failure in a refrigerator is quite rare, the vast majority of refrigerators get replaced because things like door seals, hinges or shelves break or they're just out of style. Still there are many 40-50 year old refrigerators out there that still work. We have a 1973 fridge at our cabin that has been in continuous service since then, it has never had a problem with the hermetic system.

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