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Old 05-10-2022, 05:52 PM   #41
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Default Re: A/C Refrigerent Line Pressure Switch

Finally sorted out the suction hose mixup; I will post the results of that later so that it is documented for anyone that comes across this in the future.

I now have the system under vacuum, and am going to wait overnight to make sure it still shows a vacuum in the morning.

But - I have a stupid question. The compressor came with 3oz of oil in it, and I added 2 more oz and 1/4 oz of dye to the compressor and filter/dryer (combined, not each).

I watched a different You Tube video and the guy was saying that vacuuming the system removes the oil so you need to be sure to add oil via an oil injector when you recharge it.

That really got me thinking....I'm not vacuuming out my oil, right? I mean, there isnt any oil all over the floor by the vacuum pump, so unless it vaporized it I don't know where it would be other than still in the system. It also wouldn't make sense that the compressor would come pre-charged with 3 oz of oil in it. But at the same time - how are we pulling a vacuum on the system without removing the oil?

If the gauges still show vacuum tomorrow morning, am I good to recharge? I don't want to fry this brand new compressor because of something stupid like a lack of oil...
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Old 05-10-2022, 07:11 PM   #42
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Default Re: A/C Refrigerent Line Pressure Switch

The vacuum will not remove the oil. The vacuum removes gas molecules bouncing around, and the oil is sitting on its butt as a liquid; little-to-no oil molecules are floating around to be removed.

Just checking... your pump will get the vacuum down to 29" Hg or lower?
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Old 05-10-2022, 07:54 PM   #43
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Default Re: A/C Refrigerent Line Pressure Switch

Strictly my personal thoughts as a diyer and not a professional with a license in hvac systems and years of repairs to speak of. When a repair is completed oiled/dye added and a vacuum is created, an initial vacuum around 10-20 minutes for most vehicles should result in a near absolute vacuum, 29.99in hg@sea level (a little less as elevation from sea level increases). Shutting off pump should not result in this evacuated system allowing air and moisture back in and the best time to determine if repairs were done correctly (zero vacuum change). Be aware that every seal is strained, including hose fittings, hose connections to gauges, manifold valves and gauges. If the vacuum creeps back to zero then the question to ask is where is the leak? If zero leak back occurs then continue. Any leak from incorrect repairs or questionable equipment should show almost immediately or soon after shutting off the vacuum pump. Refrigeration repairs are unforgiving of mistakes if taking everything at face value and never understanding basic physics related to refrigeration and repairs. Beware of the following physics discussion and I welcome any comments to correct me.

In my repairs, every time I turned on my electric vacuum pump, The exhaust blows out a oil mist for about 5-10 minutes. If I remember, I usually wrap the exhaust (in the handle) with a rag to capture this oil mist. This is only a guess on my part as I wrestled with this phenomenon until I thought about it. Refrigerant as a gas permeates refrigeration oil. If you're familiar with deep diving, if a diver isn't trained to surface slowly as required from a deep dive, the body was under pressure in the deep and quickly surfacing allows compressed gases in our blood to 'boil' out as surrounding ocean water pressure drops. This is known as the bends as nitrogen in blood (air is 80% nitrogen) comes out of solution from a diver surfacing too quickly. This can be painful with deaths occurring to some foolish enough to disregard the perils of deep diving. The same would occur when any refrigeration system loses pressure whether from a crash or slow leak. Refrigerant remains in oil and continually bubbles out of solution. Normal vehicle ac system standby pressures vary from 40-90 psi in direct proportion to ambient temperatures. Under pressure, refrigerant is like nitrogen in our blood but in solution with oil. Generating a vacuum would accelerate boiling out remaining refrigerant. Boiling occurs because of the vacuum created, going from normal atmospheric pressure (14.7psi@sea level) to a near vacuum. Heat isn't needed to have a gas come out of solution when a vacuum is all that's needed. Boiling refrigerant would imply creating an oil mist and a mist would travel along with remaining refrigerant gas to the vacuum pump and exhausted. Once a full vacuum is created, 29.99in hg, its presumed no more refrigerant remains so oil isn't expelled. My guess is less than half and ounce is removed during evacuation. The oil misting from gas boiling out would be the oil spewed out the exhaust port of vacuum pumps and shouldn't be of much concern. My Saturn service manuals (presuming all service manuals for all vehicles) never mentions adding additional oil to makeup for oil (as a mist) removed during evacuating a system.

A key to pre lubing a repaired system is distributing oil to all major parts as described in service manuals. Major parts replaced (compressor, condenser coil, evaporator coil, filter/drier) means those parts need a specific amount of oil to balance what was removed. This guarantees starting up a new, used or rebuilt compressor having lube oil immediately. The combination of dispersed oil and refrigerant guarantees oil moving towards the suction side to continue lubricating compressors. Oil misting occurs when liquid refrigerant moves oil (some being absorbed) thru a system, returning to the compressor and discharged again to the condenser coil. Refrigerant, oil and dye continuously circulate throughout a system. Oil is incompressible and returns as a mist for the compressor to operate without creating a hydraulic lock, damaging a compressor.

The only way to know if a compressor has oil in it is to turn it with the discharge port allowed to pour oil into a container for measurement.
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Old 05-11-2022, 07:12 AM   #44
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Default Re: A/C Refrigerent Line Pressure Switch

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Strictly my personal thoughts as a diyer
totally off-topic but when i read that i saw "strictly my personal thoughts as a dryer" due to your username. i'm curious, how'd you pick it?
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Old 05-11-2022, 08:14 AM   #45
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Default Re: A/C Refrigerent Line Pressure Switch

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totally off-topic but when i read that i saw "strictly my personal thoughts as a dryer" due to your username. i'm curious, how'd you pick it?
diyer, like do-it-yourself er. Not dryer like his handle.
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Old 05-11-2022, 09:09 AM   #46
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Default Re: A/C Refrigerent Line Pressure Switch

The pump and manifold set I'm using are a rental set from O'Reilly. It only pulled down to about 25" though on the low side gauge. The high side gauge bottomed out, but doesn't have any negative pressure 'ticks' on it so idk where it actually is. Both ports are open so I presume they would have to be at the same pressure. I am at 1,278' elevation above sea level if that makes enough of a difference? Is 25" compared to 29" something worth worrying about?

@Fdryer:
I turned the pump off and left it overnight and there was zero movement on the needles when I checked this morning. Based on that I am confident that I do not have any leaks.
Edit: Forgot to thank you for all of your input throughout this project. Although that really goes for everyone on here as well. So - thank you. =)


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The vacuum will not remove the oil. The vacuum removes gas molecules bouncing around, and the oil is sitting on its butt as a liquid; little-to-no oil molecules are floating around to be removed.

Just checking... your pump will get the vacuum down to 29" Hg or lower?
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Old 05-11-2022, 12:18 PM   #47
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Default Re: A/C Refrigerent Line Pressure Switch

At an elevation of 1300' you should still get better than 28" Hg vacuum. I would not be happy with that 25", if it is accurate, but suspect that gauge is inaccurate. Small mechanical gauges like that are only good for about +/- 3%, of full-scale range, and that accuracy is usually only for the middle third of the reading range. If you can, check the pump with a gauge that reads only 0-30" vacuum, those are common and will give considerably better accuracy

The fact that vacuum held overnight is good, 25" is as good as 29" for ensuring there are no leaks
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Old 05-11-2022, 03:43 PM   #48
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Default Re: A/C Refrigerent Line Pressure Switch

I agree with billr. Below is a chart correlating expected vacuum values against sea level@14.7 psi. 28.5 in hg should be seen on your vacuum gauge. In olden days before electronics and transducers, analog vacuum and pressure gauges are considered accurate in the middle range of readings. The combination vacuum/pressure (blue) gauge met specs for hvac purposes with lower high pressure to accommodate vacuum values. The wider sweep range of vacuum is more important than pressure readings on low side. The high pressure readings of (red) pressure gauges are important to display high operating pressures. There's an old tried and true method of finger tapping analog gauges due to mechanical gearing movements sometimes affecting needle position. Tapping gauges with a finger and seeing needle movement can nudge final needle position. In vibration environments, vibration can help with needle movement. Electronic transducers are used by most hvac techs for greater accuracy and measure in microns to determine how long to keep a vacuum pump running as opposed to analog gauges and a reasonable time to run a pump.

When measuring for vacuum after a pump is shut down, both gauge valves are closed to isolate the center port. Manifolds are designed to allow gauge measurement with side/front valves open or closed.

I borrow various tools from Autozone with one exception. A fuel pressure gauge failed to measure when needed for diagnosing a misfiring issue (ignition coil pack was determined the failure). User beware when borrowing loaner tools as the last person to use it may have inadvertently damaged it and doesn't report it fearing being charged for damages. I reported the damaged compression gauge and wasn't charged for damage. This was done to prevent this tool from being stored back on the shelf then loaned out to the next unsuspecting user. The cost of loaner tools compared to more traffic into stores that can result in more purchases.
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Old 05-11-2022, 09:03 PM   #49
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Default Re: A/C Refrigerent Line Pressure Switch

I made a fatal mistake. Everything with the recharge went well tonight, and the AC was blowing cold air (although maybe not as cold as it should have been? More below).

I put 2 solid cans of 12oz R134a in the system, and when I was all done went to disconnect my manifold hoses, and I have a catastrophic leak from the high pressure side schraeder valve. I quickly put the high pressure manifold fitting back on, and grabbed a screwdriver - disconnected the high pressure manifold fitting again and pushed the schraeder valve down thinking maybe it was stuck. No luck, the hissing got even worse.

So I'm sure the high pressure schraeder valve is loose in its seat. No....I didn't check it before I installed the brand new hoses. I don't even have the tool. Stupid mistake. Right now the high pressure manifold is connected to the line to maintain pressure. Several seconds (10 total maybe?) have leaked out. The low pressure valve is just fine.

So I will go and get the tool tomorrow and attempt to quickly tighten the schraeder valve before more freon is lost.

My question here is - how do I know how much freon to re-add to the system? Or...do I have to do the unthinkable, and go back to 0, vacuum the system, and add my 2 cans again?


Side note:

Outside temp tonight was 80F with wringing wet humidity - literally my garage floor had standing water on it from the humidity. Vent temps were 'only' 60F, but they felt about as cold as my other Saturn gets. If I hadn't actually looked at vent temps, I'd have said that was good and never thought anything of it. But I've seen other posts claiming a 40F difference in vent temps? Can someone elaborate on that? Should I be seeing colder?

@Fdryer - pressures recorded at 2k rpm (before any leaking occurred) are as follows:
Low side: 35psi
High side: 274 psi
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Old 05-11-2022, 10:32 PM   #50
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Default Re: A/C Refrigerent Line Pressure Switch

It's usually presumed schrader valves are screwed in correctly with every new hose so this may be an exception. If you are describing the valve core tools to remove/replace valve cores without losing or removing refrigerant, they usually come as a set as each fitting is sized differently to prevent connecting low side hose to high side and vice versa. These tools may be available as loaners. An open system simply requires a valve core tool that are used to replace valve cores in wheels.

The problem you have is not knowing how much refrigerant was released. Repair shops by EPA regulation are required to remove refrigerant into canisters, not vent it the atmosphere. Diyers are required to do the same otherwise a large fine can be issued if caught releasing refrigerant. In reality, what the EPA doesn't see in repair shops or diyers releasing refrigerant into the atmosphere going unreported or documented is a very large gray area. The majority of refrigerant loss occurs from catastrophic damage occurring in a front end crash, mishandling by anyone unfamiliar with handling refrigerant, ignoring simple guidelines to minimize refrigerant release and accidents like yours. There are two ways to work this dilemma and it depends on which way the valve is tightened or replaced.

The special valve core tools used to service valve cores on charged systems doesn't release refrigerant while replacing or tightening the valve core. Very little refrigerant is lost this way. If a valve core removal tool isn't used then legal removal of refrigerant requires a vacuum pump to evacuate and discharge remaining refrigerant into reclamation canisters. Diyers can call around and find a repair shop willing to remove refrigerant to little or no cost. A leak would release refrigerant. The best way of determining what remains is to remove refrigerant and start all over again to guarantee the correct charge amount. A knowledgeable person can use gauges and service manual info to add refrigerant until pressures match chart specs for temperature and humidity. The key to adding refrigerant with gauges is adding a few ounces then stopping to monitor gauge pressures as the system stabilizes with adjusted pressures to compare to charts. Slowly adding and creeping up to expected operating pressures with local temperature and humidity can achieve correct amounts without overfilling. Overfilling raises high and low side pressures above chart specs, loads the compressor and engine while creating more heat from higher discharge pressures. This may raise vent outlet temps too as the point of no return is reached. The trick is knowing when to stop adding refrigerant.

With r134a systems, there's a fixed amount of total volume to accommodate refrigerant, oil and dye. Adding more simply reduces the volume and increases operating pressures decreasing cooling efficiency. Honest mistakes occur to anyone including professionals.
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Old 05-11-2022, 10:44 PM   #51
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Default Re: A/C Refrigerent Line Pressure Switch

Do you happen to have the pressure charts? I can calculate the temperature and humidity and get to the right pressures if I know the numbers to shoot for.
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Old 05-12-2022, 08:00 AM   #52
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Default Re: A/C Refrigerent Line Pressure Switch

Quote:
Or...do I have to do the unthinkable
I'd probably do the unthinkable. It it's leaking anyway, just let it finish.
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Old 05-12-2022, 11:33 AM   #53
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Default Re: A/C Refrigerent Line Pressure Switch

Me too. I have come to the conclusion that is the easiest (only?) way to ensure charge is correct, unless you know the system components are all OK. Gauges can help trouble-shoot a system, if the charge is known to be OK; or can be used to check charge if the system is known to be OK.
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Old 05-12-2022, 11:35 AM   #54
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Default Re: A/C Refrigerent Line Pressure Switch

UGH. Absent any pressure charts or anything to meaningfully guide me here that's where I'm leaning as well.

This never showed on the vacuum leak test because the manifold fittings were holding the pressure. So what I want to do is tighten that valve (or otherwise assess why I think it may be leaking) and then pull vacuum again.

And once it's under vacuum, I want to completely remove the manifold fittings from the equation. Leave the system under vaccuum with everything totally disconnected, and then the next morning, reconnect the manifold gauges and hopefully measure the same vacuum pressure that I had prior to disconnecting it the night before.

The reason for doing this is to make absolutely sure this time that my schraeder valves are holding pressure before I go tossing another 2 cans of freon into the system.

My question is - will this idea work for what I'm trying to test? Or will connecting and disconnecting the manifold gauges somehow release vacuum or otherwise invalidate the test?


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I'd probably do the unthinkable. It it's leaking anyway, just let it finish.
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Old 05-12-2022, 03:12 PM   #55
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Default Re: A/C Refrigerent Line Pressure Switch

Disconnecting then reconnecting into an evacuated system presents issues. The manifold gauge set, if they're in good working condition, should retain their last vacuum measurement with both valves closed. This relies on both quick connects and screwed fittings free of leaks, gauges fitted onto manifold free of leaks and both valves free of leaks. My quality set of gauges and hoses will leak after disconnecting from a system the next time I use them. Nearly new. Nothing's perfect. I don't expect them to retain low and high pressures because of their complexity using tried and true mechanical designs that haven't changed and don't need improvement. The hvac community is world wide, using the same manifold sets for decades as testament to their durability for everyday use in a vast industry. Quick connect fittings are designed for minimal release of refrigerant. They weren't designed to work in vacuum scenarios as this suggests the moment a quick connect is connected, the momentary opening of the Schrader valve before a sealed connection occurs will allow atmospheric pressure into the near perfect vacuum resulting in a lower vacuum value. This would be seen on the low side gauge connection. Connecting the high side gauge would repeat another momentary atmospheric pressure intrusion into this vacuum. It's presumed valves are in working condition and relied on when they're expected to close when fittings are removed. Unfortunately you became a victim of circumstances.

The impractical application of reconnecting to a system already evacuated presents another issue. Schrader valves are mechanically designed to prevent pressure from leaving. Pressure and the spring loaded valve with a valve seat using a synthetic rubber as seal work together to keep the valve closed. Personally, I think they're not designed to work in a vacuum where atmospheric pressure is trying to force the valve into opening. If a vacuum were needed for hours then a different valve would be necessary, complicating things by possibly having a different set of hose connectors.
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Old 05-12-2022, 04:24 PM   #56
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Default Re: A/C Refrigerent Line Pressure Switch

Do you have a suggestion on how to verify that my valve isn't screwed before I put more refrigerant in? (Pun intended).

If I pull vacuum down to 25" like it was before, disconnect the gauges, and reconnect the low side only in the morning, and see even 20" of vacuum remaining, that will confirm there are no catastrophic leaks from that valve right? Or are you saying that atmospheric pressure will depress the schraeder valve and let itself into the system when the system is under vacuum, and this is an invalid test?

Trying not to repeat the same mistake twice here...


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Disconnecting then reconnecting into an evacuated system presents issues. The manifold gauge set, if they're in good working condition, should retain their last vacuum measurement with both valves closed. This relies on both quick connects and screwed fittings free of leaks, gauges fitted onto manifold free of leaks and both valves free of leaks. My quality set of gauges and hoses will leak after disconnecting from a system the next time I use them. Nearly new. Nothing's perfect. I don't expect them to retain low and high pressures because of their complexity using tried and true mechanical designs that haven't changed and don't need improvement. The hvac community is world wide, using the same manifold sets for decades as testament to their durability for everyday use in a vast industry. Quick connect fittings are designed for minimal release of refrigerant. They weren't designed to work in vacuum scenarios as this suggests the moment a quick connect is connected, the momentary opening of the Schrader valve before a sealed connection occurs will allow atmospheric pressure into the near perfect vacuum resulting in a lower vacuum value. This would be seen on the low side gauge connection. Connecting the high side gauge would repeat another momentary atmospheric pressure intrusion into this vacuum. It's presumed valves are in working condition and relied on when they're expected to close when fittings are removed. Unfortunately you became a victim of circumstances.

The impractical application of reconnecting to a system already evacuated presents another issue. Schrader valves are mechanically designed to prevent pressure from leaving. Pressure and the spring loaded valve with a valve seat using a synthetic rubber as seal work together to keep the valve closed. Personally, I think they're not designed to work in a vacuum where atmospheric pressure is trying to force the valve into opening. If a vacuum were needed for hours then a different valve would be necessary, complicating things by possibly having a different set of hose connectors.
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Old 05-12-2022, 05:16 PM   #57
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Default Re: A/C Refrigerent Line Pressure Switch

Performing ac repairs doesn't allow for experimentation that allows introduction to other issues. Taking short cuts doesn't work with refrigeration repairs. Connecting gauges allows you to monitor two pressures once a system is charged to verify correct operating pressures as well as detect incorrect pressures as the only way to determine where a problem lies. It's like covering one eye; losing stereoscopic vision seeing everything in three dimensions now cut off with only one good eye. Or losing hearing in one ear. No one can predict repairs will turn out perfect except for those simple things like putting the cap back on the ketchup bottle so it won't spill out when turned upside down. Refrigeration repairs are not diy friendly at all.

Your best option is either using the special valve core removal tool or remove remaining refrigerant to assess why the high side valve was loose. It may be a defect in manufacturing but until you get past losing refrigerant, you're left to ponder choices. Most aren't addressing the value issue that should be examined up close without a valve core tool. Try not boxing yourself in.
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Old 05-12-2022, 08:40 PM   #58
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Default Re: A/C Refrigerent Line Pressure Switch

The nightmare continues.

The valve core was not loose in it's seat. So I removed it completely and found 2 distinct metal shavings wrapped around the sealing portion of the core. That explains why it wasn't holding pressure.

The million dollar question now is....where did those metal shavings come from? Is it possible that they were leftovers from the machining process for the valve core seat? Is the compressor self destructing already? I can unequivocally attest to 5oz of PAG 100 oil being present in the system. The new compressor and system has 1 hour on it so far, and I flushed the evaporator core and every other component was replaced with new.
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Old 05-12-2022, 09:06 PM   #59
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Default Re: A/C Refrigerent Line Pressure Switch

Post a picture of those shavings. Zoom in so we can examine them, and put a penny in the picture so we can gauge the size of the shavings.

PS: any guess what metal they are? Use a magnet to see if they are ferrous, sodium-hydroxide for aluminum.
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Old 05-12-2022, 09:48 PM   #60
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Default Re: A/C Refrigerent Line Pressure Switch

Let me know if this doesn't work. There were 2 of these, I found one on the garage floor, I cant find the other one. They were about the same. They were literally wrapped around the core and I was like 'what the heck is this on the valve core?' so I picked at it with my fingernail and it fell off on the floor.

It is not magnetic. I don't have sodium hydroxide.

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Post a picture of those shavings. Zoom in so we can examine them, and put a penny in the picture so we can gauge the size of the shavings.

PS: any guess what metal they are? Use a magnet to see if they are ferrous, sodium-hydroxide for aluminum.
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