This air compressor will fail 

Working in a garage at a car dealership, I once had a stroke of brilliance where I decided to see how far I could shoot an empty soda bottle. I poked a hole in the cap, stuck it on my air nozzle and squezzed the trigger. About 10 milliseconds later the bottle exploded with an explosion that I'm sure troubled a lot of customers in the waiting area. It also troubled my boss, who troubled me about it.

Hi Matthias. Very nice video! I am an antique and vintage refrigeration repair guy. I love this stuff and have made many videos! Your compressor is a high-side housing compressor as you know. The output from the rotary pump goes into the motor housing. Boyle's law applies with all gases including air. The rise in pressure ratio; comparing the absolute pressure of the inlet versus the absolute pressure of the outlet determines how much the temperature rises. The fact that the original refrigerant was coming in at a much higher pressure limits this ratio and therefore the discharge temperature. You'll need to limit the discharge pressure accordingly to prevent some extreme discharge temperatures. It will likely last a long time as you are using it, assuming you don't run it for extended periods of time. Laughed a lot at the soda bottle with shavings exploding! The one real worry you need to consider with this compressor is that it does compress air into the motor housing, with the motor winding and oil. This may not seem like a problem; however you need to think about the chemicals involved. Refrigerant and oil never react. Air and oil can react, in a combustion reaction. If the compressor overheats badly and the oil reaches its flash point then something inside fails and creates a spark, there can be a flash fire inside the compressor. This can create a massive pressure all at once. Normally this won't rupture the casing, but with older compressors and rusted casings it can. There have been fatalities as much as I hate to say that. You won't have that problem as long as you keep the run cycles short and the temperatures low. Back in the early 1930's General Motors, in their Frigidaire division, invented a compressor called the Meter-Miser. It was highly energy efficient. This used an orbiting cylinder in a round chamber, with a moving divider block to create a pumping action. This design was used for many decades and there are still plenty of them around today. The design was sold to Matsushita (Panasonic). Eventually the design became public domain and many Far East manufacturers copied it. Yours is a rotary compressor based on the Matsushita design. It isn't actually a scroll compressor. Scroll designs are low-pressure housing designs and operate on a different principle from the Matsushita rotary. Both designs are good, but different. Refrigeration history fascinates me! I have items in my collection as old as 1926 and am delighted to talk about them. It's one of my passions. I have posted two more comments with more links. Hopefully Matthias will approve it and allow it to share.

What you have there is a rotary compressor. Internally, the motor is at the top of the unit and the compressor mechanism is on the bottom. Both rotary and scroll compressors have higher volumetric efficiency than reciprocating types. The vessel on the side of the compressor is an accumulator. It captures any liquid refrigerant that happens to make it back to the compressor and holds it, pulling only the vapor into the compressor since the liquid is not compressible.

It's been a while since I studied pneumatics, but back then we were advised never to block off a pressurised line with any part of our body (fingers etc.) because of the risk of causing a bubble in the blood which could lead to an embolism.

I've watched a few of those "convert a refrigerator compressor to blow air" videos, and this has been the most informative by far.

Seems like it would make a great second stage for helping your regular compressor go above 100psi. More efficient with already compressed air, and less duty cycle from doing work outside its efficiency range, and also pre-filtered air, so a lil less condensation.

Do not worry! I have been using such a compressor for 2 and a half years. Mostly for normal purposes like car tires or blowing dirt. I even painted the fence with it. I fitted him with a LPG bottle. after the bottle, I put an "oil trap" and pumped the oil through a precipitator and back into the compressor! BUT IT IS IMPORTANT THAT THE OIL IS AUTOMOBILE "0W-30". The problem is that winter is sometimes hard to start because of the thick oil. But it works without a problem. There is also a fan to blow the compressor itself. Also, it works no more 100-150psi (10 Bar) with pressostat and separate pressure releaser + check valve between the compressor and the bottle!

Man, do I love it when engineers have the freedom to play around with destructive toys. You could have an entire channel dedicated to this line of thought and it'd be a smash hit, guaranteed.

Ah the scroll.. I was a mechanic in the secret scroll machining room at Copeland Corp in Lebanon Missouri. Interesting place to work in the layer 90s. Was paid $5000 to keep my mouth shut for 3 years about the manufacturing process. The shaft in the center your mentioned is called a "green shaft". It utilizes garlock bushings. Takes an incredible amount of work to create the orbit and base scroll. 4 cnc machine with multiple tooling per machine. Then they have to be lapped. That's done on a machine called an "aspenizer". Then the "luberight" dry lube system. That is basically non phosphate parkerizing. Anyway cool to see a project with one. They are the best compressor made. I personally own one.

Heyhey, AC dipl. technician from germany here :) a few tips: dont turn the compressor on its head or turn it on when its upside down, the rotor etc can fall out of its bearing. And dont pump oil with it, the hydrolocking can damage the valves. Use an oil trap to recirculate it into the intake. And finally, visit the manufactures website on information which oils you can use. I recommend all ester oils

Air compressors for work shops have oil coming out the line anyway. Hence the filtering if you do spray shop painting. So I wouldn't worry. It's partly by design to keep air tools lubricated.

Matthias, you never fail to entertain, and educate

These compressors are really nice for small occasional hobby use at home where noise and price is a issue. I’ve put together mine with a 6 liter tank from a old compressor that was scrapped along with fine moisture/oil filter and pressure switch. It’s a bit slow building to very high pressures, but works excellent for blowing out dust from electronics, airbrushing and pumping tires, which is what I’ve been using mine for. It’s nice that I don’t have to worry about bothering neighbors too given living in an apartment, where people would get annoyed if I wanted to use it later at night, and most of the components were salvaged for free.

With all the leakage issues, I just realized this guy must be the lead engineer for the Starliner.

To help keep the compressor from having issues with water collecting in it, before putting it away after experiments, run it with no load for a minute or so to evaporate and remove any water that built up.

I used a similar compressor to build my first refrigerant recovery machine . That was well over thirty years ago. I was on a budget and the EPA was requiring you to capture refrigerant rather than release it to the atmosphere. I even registered it with the EPA. I designated it as the " SUX 2000". It worked well until I was able to afford a real one.

Matthias, Thanks! Always wondered about the way the pressure was increased. Scroll seems great!

Very thorough, thanks for covering all the points brought up.

Old ones would die pretty fast after oil starvation (assuming you'd dump all the oil out). These newer units are ... less susceptible to the issue, tho i think that's because of the inherent robustness of sintered parts rather than "better parts". Even so, the death would occur after a loooong long time. I have one of these for an automated air tank that compresses air and decloggs a vent twice a month. I think it's been ~7 years since i fabricobbled it together, never once had to work on it.

Great explanation of the scroll compressor.

I have a buddy that's a mobile mechanic, not sure of his exact set up, but he has a re purposed ac compressor that feeds a custom built air rank in his van, making a whole lot of extra room in the truck. Biggest thing is an ac compressor doesn't produce a lot of volume of air, so it takes time to build up the tank.

That's not a scroll compressor as you suggest - it's a rotary compressor (an eccentric rotor spinning in a chamber with a stationary spring loaded vane and a couple of reed valves). I'm not sure how much cooling would be had from the refrigerant on rotary style compressors anyway, as the motor windings are on the high-pressure vapor (hot) side of the compressor, so no cold returning refrigerant vapor to wash the inside of the motor like a scroll compressor has. The desiccant chamber on the side is actually an accumulator, designed to boil off any liquid refrigerant that may be entrained in the returning vapor from the evaporator.

Lots of valid points and cool experiments. I used a window unit compressor and an old fire extinguisher tank to build an airbrush compressor, I drilled an oil port in the base and installed a drain plug for easy oil maintainance, the pressure switch is set at 80 psi max, the inline water/oil trap combined with a regulator helps with moisture ect. the airbrush hose has a secondary filter/trap. So far it's been working fine, the airbrush uses about 20 psi max and mostly around 12-15.

Do add a input filter to avoid it filling up with wood dust. Also, I am sure you can arrange a oil drip lubrication if you wanted. a check valve on the low pressure side may help it hold pressure too.

Love that you're putting a bicycle valve in the pop can top at 7:18. I did this years ago when I was screwing around (after being told pop bottles could hold quite a bit of pressure)... Never tried to burst one, but I've also heard the threads are intended to fail first.

Had never heard of a scroll compressor before, interesting mechanism. Thanks for sharing

Bambi and Sil-Air sell air compressors that use fridge style compressors. They are occasionally sold as dental air compressors with multiple compressors so they can fill a large tank quickly and, more importantly, quietly. You can solve some of of the lost oil problem by making a coil of copper tube above the compressor, so that the oil condenses in the tube and then drains back into the compressor. These, if done properly, can actually provide decades of service. In fact, air compressors with these style compressors are a popular choice for fine airbrushing due to how quiet they are.

Well I’m sure you’re going to get this a million times but here goes. Eastwood does use a scroll compressor for there shop compressors. I personally have one and I can say it is incredibly quiet for a 12.5 CFM compressor and they clearly went through some effort to ensure limited amounts of oil make it though the output but yes it always has a bit of oil in the compressed air.

My car 12v tyre compressor has a screw on connection to the tyre valve. That’s what you need for your crazy experiments. Keep up the good work. 👍🏻

The compressor is a A rotary compressor. The rotor is on the bottom and the suction pipe has a separator or a suction Receiver to keep the compressor from getting liquid refrigerant.

I feel like a sweated fitting on the output would benefit you greatly as well as a water oil separator and even a small tank to reduce cycle times on the compressor. even a filter on the input to help

When I was a kid, my dad and I made a water rocket out of a 2 liter bottle by attaching a quick connect through the cap. This served as both the fill port and the rocket nozzle. We discovered that the bottle could withstand 120 psi... a couple of times. We were refilling it after the 4th or 5th launch and there was a loud explosion. The bottle was gone. We found it later off in the woods with a huge hole in the side. Luckily we were smart that day and were not holding it while it was filling.

Sealed compressor pumps are actually used as compressor heads. combined with a small receiver tank, pressure switch, oil separator, etc. they can be very effective for small applications. I use one as a vacuum pump. Works a treat.

Had no idea about the scroll mechanism. Awesome stuff as always

If there is a better channel than this on Ytube, I've never found it.

I'm so glad you went over the scroll compression. That is one of my favorite inventions. Yes, they are horrible for low pressure, and as you also stated the oil is transferred along with the compressed gas, but still a phenomenal feat.

The biggest risk for bun up is that you've changed the design load and that will alter the power factor correction of the run capacitor. But that is only if you run it for long periods, whereas you will be doing intermittent duty. There are calculations to determine a new run cap value, but probably easier just to measure power factor with various capacitor values. The precipitation of moisture is the same problem that is with HVAC vacuum pumps and the need to change the oil during pump down. Those units use a bypass that draws in a bit of fresh air to keep the partial pressures out of condensation range during the start of the process then close it off to get the deep vacuum.

I've seen them used in printing equipment to drive pneumatics. They have a sight glass to check the oil level and the oil blow-by is actually a good thing since it lubricates the cylinders. Kind of acts as a central lubricator for the entire machine.

Wow! I never knew there was oil in there! AND you can change it? I learn so much watching you, Mattias!

Well... I don't remember for what exactly you're going to use it, Matthias. 😬 But, if it ever fails, I believe the refrigerator's compressor is pretty strong! And many times people throw off old refrigerators with perfectly good compressors! Anyway, stay safe there with your family! 🖖😊

Kinda impressed with how well wood works as makeshift pneumatic fittings.

**********The device on the suction line on the side of the compressor is an accumulator to stop excessive liquid refrigerant from dragging the oil out of the crankcase and also keeps the scroll from damage from trying to pump liquid. You can probably cut it off. Although I’ve not run across an accumulator that had desiccant installed, it could be implemented as a manufacturing cost savings…. Love your technical videos….Retired HVAC/R guy here Oh, For years small compressors were repurposed as vacuum pumps and whatever. I have an original Whirlpool ECP127 vacuum pump that uses a large domestic refrigerator compressor….and this thing has been left running for more than 24hours multiple times a month with no problems….and it’s 53 years old. If it works..you win! If it fails, get another one and make it work!

So if the current compressor container should rust out, I can replace it with a soda bottle, good to know :D

"I've had enough of all this leakage!" *poke* _poof_ Me: "I wonder what the particle counter says now?"

If you're still playing with it, some soap on the end grain of the wood adapter block may (or may not) be interesting to see how much air gets through the wood fibers.

the piece on the side should be an accumulator and not a desiccant...rotary compressors like this will have an accumulator to catch liquid refrigerant and oil to prevent it from entering directly into the pump and causing damage. the biggest issue with using these for an air compressor is that their compression ratio is typically designed at less than 4 to 1...typical return pressure around 130 and discharge 350, so exceeding this will likely be the biggest threat to reliability

Another reason you may not want to do this is that refrigerant compressors can diesel. It's rare, especially at the pressures and temperatures we are talking about here, but not inconceivable.

I turned a compressor from a water cooler into a vacuum pump. It had three copper pipes coming off of it. One of them needed to be sealed off, so I crushed the pipe closed and soldered it closed. I put some shop towel around the exhaust to catch any oil, and used some 1/4" compression fittings used in swamp coolers to adapt the copper on the intake side to some 1/4" irrigation line that I had laying around. I used a mason jar as the vacuum chamber, so I drilled two 1/4" holes in the lid and pushed the irrigation line that was hooked to the pump in one hole, and my vacuum release line into the other. For the small silicone and epoxy projects that I needed this for, I just needed to degas after mixing, so to seal off the irrigation line, I just added a liberal amount of hot glue to the inside and outside of the lid. For the vacuum release valve, I just took two coke bottles and cut off the very top. I sanded until I got to the rim just under the threads, and glued both necks together with more hot glue. One cap got a 1/4" hole for the irrigation line and plenty of sealing hot glue. To break the vacuum once I'm done, I just unscrew one of the coke caps. I usually just used it with a small mason jar, but I did use it with a quart size jar a few times.

I think that the biggest risk to the compressor’s life will be from the compression ratio. Normally, you might have between a 1 to 4 ratio up to 1 to 10 depending on your suction pressure. But when pulling air from atmosphere your suction pressure is going to be below zero and your discharge pressure will be whatever you pump it up to so your ratio will be very high. That said, if you do end up killing it, you shouldn’t have much trouble finding another one. Have fun and be careful.

I have a friend who has a booth at the state fair every year. She air brushes caricatures of folks onto t-shirts. She uses an old refrigerator compressor and a bank of 2-liter soda bottles as her air tank. She has the shut off set to 40psi. I'm not sure what pressure she needs to spray but, I assume it's half of that. Anyway, she cut her compressor open and made flanged rings for the two halves so she could bolt it together and open it up after every year and dry it out and replace the mineral oil. She replaces the soda bottles regularly but, has been using the same compressor for the entire 22 years I've known her. Just thought I'd throw my 2¢ into the works.

Yet another great video.

I used an old fridge compressor for years to recharge my 100psi air tanks. I did install an oil/water separator and a pressure shut-off switch.

Really interesting and nicely hands-on :)

1) You might like to add a drain plug to allow easy removal of water and replacement of the oil. 2) An oil trap with an area of low flow or cyclone flow will help remove the oil from the air.

The moment he lose patience with the soda bottle is hilarious! Education and Entertainment.

I've enjoyed using these scroll type pumps as a crude vacuum pump, never measured vacuum, but for filtration it's fine.

That appears to be a rotary compressor not a scroll. Why'll it will probably last a long time pumping air, because the piston rolls inside the housing. The one thing to be mindful of is the shell is full of oil, and is pressurized to discharge pressure. Therefore a potentially dangerous condition exists, that of superheated fuel/air mixture that might meet its flashpoint.

this video has it all! explosions , things to make people argue about, an awesome diagram, and even some 2x4s!

when I made my fridge compressor-compressor I added an inline oiler unit to act as a carburetor and lubricate the internals, and then used an oil separator on the tail end. I also used an electronically controlled dump valve between the compressor and the check valve that went to the tank. This unloaded the pump so it wasn't starting up with a high resistance when trying to fill a partially filled tank. I used the whole unit daily for 5ish years before upgrading to a larger compressor/tank.

It might overheat if you leave it idle, but the good news is, under normal flow it's always sucking in fresh cool air and expelling warm/hot compressed air (not recycling hot gasses) so it may reach an equalibrium temperature.

When I was a kid, dad fixed refrigeration systems for people, from auto A/C to refrigerators to home air conditioners. He had a compressor he'd taken out of a broken fridge that he used as a vacuum pump, and he used it for years. I'd never tried to use an air compressor to rupture a soda bottle, but I've done it plenty of times with dry ice!

I have been using silent airbrush compressor called Sil-Air for years, I have used it for everything including vacuum, it’s made of air conditioner compressor, it also have automatic pressure that disconnects the power to the compressor when it reaches pre-set pressure and have pressure regulator with oil and moisture filter all those can be retrofitted to any air compressor.

I enjoyed this. Thanks.

It was the first time I saw a explanation of the house scroll compressor worked that made sense.

Awesome stuff as always😀

I've been upgrading my vacuum pumps in the lab to scroll pumps. They are quiet, efficient and they do not mist or leak oil. There are seals on the tips that wear.

I used to pump soda bottles up to ~100psi for a project and didn't have a single failure...until one unexpectedly failed after I became comfortable around them. It sent some plastic shards in my eyes and really messed up my eardrums for a few days. Plastic shrapnel in the eyes is not fun. I would not do it again.

You could always put an air oil separator on the output. Autobody shops have them on the air lines for the paint booth so you could always buy one or make something similar and just keep an eye on how much oil has come out and replace the lost oil from the compressor. I was thinking weigh the separator when new then weigh it again in a week or so and add the weight gain back into the compressor. My friend used his jeeps ac compressor for onboard air for filling tires when he went 4 wheeling.

I ran a 1/4 hp piston compressor for several years, only added oil one or twice. Ran great, used a truck muffler as tank, never failed. I did had to drain water out of tank, of course.

That compressor isn’t a scroll compressor. It is a rotary compressor. That’s why it increases in size in the suction line to eliminate any liquid because the gas is going right into the compression chamber of the compressor.

Would work well as the second stage after a piston compressor, or even a fan just to slightly pre-pressurise the air.

I saw an e.Europe guy like to use these as a home brew vacuum pump to evacuate the lines for diy AC work. Instead of an air compressor, it could make a decent infrequent vacuum pump.

You are doing some pretty crazy stuff :)

My dad used a compressor from a car as a compressor for years. We just put 10w30 engine oil inside it. A few drops occasionally, to replace what was lost. It would make oily water. But not bad. The tank had a small leak. So it kept drained out.

I've been using that kind of compressor for pressure testing various aircon parts. From hoses, evaporator and condenser.

I can't believe the timing of this video. Two days ago, I dragged a discarded-but-still-working window a/c from next to the dumpster and extracted the compressor--it looks just like this one. Now I'm excited. I've got a 5-gal air tank from HF I'm going to hook it to. I think I'll make an inline filter from PVC and stuff it with polyfill to trap the oil mist. I think I can get an idea of when to top up the oil in the compressor by weighing the fiberfill every so often. I think I'll also add some valves and tubing to make it reversible: sometimes a compressor and sometimes a vacuum pump (for degassing resins, etc.).

With a regular compressor inline ahead of it a lot of the moisture would condense out and you could use this one just to boost the 120-150psi up to 300psi. The oil coming out could be passed through a filter before use. I run a small CNC machine using compressed air as the coolant. The small air compressor has to run almost constantly to keep up, so a small and quiet compressor like this would be ideal. There are literally bins full of these compressors at the scrapyard and also small appliances being dumped all over the city every day.

Mine lasted around 8 years, I just replaced it a few weeks ago. First one I gave very little love, just poured some kompressor oil into the intake 2 times in 8 years. It was attached to a pretty well sealed system but hooked up to power for the better part of thoose 8 years.

There are scroll air compressors, but generally they go from piston to screw/roots. For air compressors generally scroll and screw are oil free, while piston can be oiled or oil free. Scroll air compressors are generally used in lab or medical due to the low noise. Piston is the low to medium shop usage. Screw/roots compressors are for large shops and industrial applications. You can get screw blowers in 1000s of cfm. Screw and scroll do the best with variable speed.

I’ve been using the Evaporator coil from a window air conditioner as an auxiliary transmission cooler for years

This compressor is a rotary compressor, I.e. stationary vane with an offset lobe that traps vapour. You can identify scrolls by the absence of a factory installed suction accumulator (the small black vessel fitted to your compressor), and the inlet, or suction line is almost always towards the top of the compressor body. Rotary compressors are the only compressors fitted with suction accumulators from factory, and with the majority of the compressor body being the high pressure side. This is why your volume is so great when compressing air. Scrolls would have minimal volume due to the design as you drew.

Really cool! Thanks.

What we did as kids with the bottle is the bicycle valve but we removed the valve inside that just screws out, made attaching a normal pump way easier and yes we exploded them by hand, just like 1m away from the bottle.

POE oil is hydroscopic. Yes, in a refrigeration system the coolant does cool the compressor. Refrigerant returns superheated about 20⁰ to 30⁰ degrees above its evaporation temperature of about 42⁰. (AC system) Refrigeration compressors running without refrigerant often cycle on thermal overload because no cool return gas.

I suggest trying to use it as a vacuum pump next :) That's what I'm trying to prep mine for. Careful with the chamber tough, implosions are not nice

Some compressor applications like painting do need to worry about oily air on the output, you'll need a catch can for that.

I have been using a fridge compressor on a 8 litre tank for a truly silent air brush set up for about 3 years now, all I did was measure the amount of oil I drained and replaced it with an equal amount of full synthetic 0W35 castrol oil. The oil mist is a real issue but I have a SMC micro-mist air/oil separator that removes 99% of the oil and water before it reaches the tank the water trap on my regulator has never had any condensate accumulate. As long as you replace the oil that escapes it will keep going for a long time.

Scroll compressors are super efficient and oil-less in the medical field. The scrolls have tip seals and grease on the bearings to prevent wear.

Back in the early days of my cabinet making I worked for a guy that had a refrigerator compressor for a pump, a big truck tire for a tank and we used that to build cabinets for 3 years.

The 2 liter rocket with it's shavings payload was successful for multiple launches! Alas, like most programs, interest and/or funds wane so it's brought to an end...in this case with loss of vehicle and payload....but in spectacular fashion!

There is a commercial air compressor vendor in Denmark, Jun Air, that has been selling quiet and compact air compressors using Danfoss refrigerator compressors for probably over 50 years by now. It's proven to work just fine.

That is a rotary compressor without a doubt, and when people say the refrigerant cools the internals it means that the cool lower pressure suction gas cools the internals, it's typically below 50°F gas coming back to the compressor, also the suction pressure doesn't matter when it pertains to how hard the compressor is working, what matters is the compression ratio. Typically on an airconditer you would have around 150 psi on the suction and 300 psi discharge which gives you a compression ratio of 1.9. What you are doing here is essentially 0 psig suction pressure and whatever pressure you decide to pump the tank up, say 150psi. A similar compression ratio. All things considered that compressor will likely survive a long time due to the fact that you will be running it for short periods of time.

Always fun to watch 🙂

They also make great vacuum pumps as well.

I would love to know more about how oil-less and ‘silent’ compressors work and if they’re DIYable!

The double spiral thing is genius.

Hey Matthias! A carbonation cap with a ball lock would be a great way to get pressure into that soda bottle without leakage. I've personally had a 2L bottle burst due to a faulty CO2 pressure regulator on my tank. You can find them on amazon for about 25 bucks.

this is so cool. i should find something like it and put a small solar panel over it with an external air tank to have an outdoor unit for air tools

You said it. the atmospheric moisture will eventually doom the unit, but that will take many years. My unit is well over 10 years old and still runs strong. I have it plumbed to an old inverted r22 bottle and I dribble a little oil in every time I start it up.

These scroll-compressors were used in the 90th by Volkswagen in the "G-Lader". Had the honor to drive a Corrado G60. The G-Lader sounds really angry, makes a lot of fun but has often problems with leakage and needs expensive service.