Instructables

What lubricant to refill a fridge compressor with?

Hey all, I just grabbed a compressor from a fridge that had been badly mangled by a bulldozer at a demolition site, planning to make a vacuum pump or airbrush compressor (or both!) Trouble is, I thought the liquid it contained was leftover refrigerant, and drained it all out. I didn't really have a choice, as leftover freon was gassing out of the compressor (thought it had lost pressure, but there was still a little in the compressor) and it was sputtering the oil everywhere. I held it upside down while carrying it home, and when I got it here, it was apparently empty. Then I found out that what I poured out wasn't liquid freon, but actually vital oil that keeps it alive. The compressor runs fine, but I only tried it for a few seconds for fear of destruction. I have many lubricants here, motor oil, 2-stroke oil, bike chain oil, etc. If I'm to dump an oil into my compressor, any ideas on which is the best call, and roughly how much should it take?

Clearly Rectifier has done his research and has learned through direct experimentation. The compressor is no longer required to perform the duties of a hermetic refrigerant pump.
When repurposed as an open loop air pump (air compressor) the lubrication requirements are exactly as he stated: "non-foaming, non-conductive, and light enough to be sucked up by the hollow crankshaft". Additionally, Rectifier mentioned that using a compressor indoors can be problematic due to oil vapors. Mineral oil is the most logical choice.
Rectifier, I wish I could tell you the oil capacity of your compressor but you probably already know that having a manufacturer's name, part number, and the Google search engine will get you nothing but Chinese export salesmen trying to sell you a pallet of compressors.
You probably already know that the vacuum ports are not isolated from the oil supply like the pressure port. Too much oil will block off the vacuum ports or cause leakage. You could clean out the old oil and determine the maximum capacity of your compressor in one operation: Fill a graduated container with a suitable solvent. Cut an opening in the unused pipe stub (the #3 factory crimped pipe). This is referred to by several names but it is essentially a vacuum port and it is at the same level as the original vacuum port. Hook a funnel and some tubing into one of the vacuum pipes and begin pouring solvent into the funnel. Stop pouring when the other vacuum port begins bleeding solvent. Record the result and now you at least know the absolute max capaity of your compressor and can avoid overservicing it. Reseal that third pipe and affix a non-collapsable hose to your #1 vacuum line. Fill a container with your calculated amount of mineral oil and submerge the vacuum hose in that fluid. Turn on the compressor (yes, there is no oil in the sump). Watch the cup of mineral oil; an airtight and healthy compressor will suck up all that oil in 1-2 seconds. Of course, shut off the compressor if it fails to scavenge the oil. Good Luck sir and keep us informed!

Please notice that these posts are date-stamped.
Rectifier asked about this more than 3 years ago, you'd hope he isn't still waiting...

L
Goodhart6 years ago
It depends on the compressor: An R12 type system uses a special form of mineral oil, while an R13 system uses either an Ester-based oil or a PAG oil. Oils not made for the compressor could break down after continued use.
Rectifier (author)  Goodhart6 years ago
The compressor says "R-12" on the side. What kind of special is the mineral oil? Is it considerably different, then from an ordinary light mineral oil (say, 10W30 automotive oil)? Also, is the oil only special due to the requirements of the fridge while operating as a fridge? As it now will be running on plain air rather than R-12, and in an open system rather than closed - so I would think it no longer needs to do things like scavenge water? All it needs to do is be slippery and the right weight? When it comes to oil breakdown, would it be OK to just change the oil once in awhile - I don't mind if the compressor is being slowly damaged, I can always find another one if it dies in a year or two. It's more that I don't want it to lock up within a month while I've just built it into something. jackalope - Fridge compressors are weird. The oil inside is somehow also exchanged with the fluid being pumped. Or that's the idea I get from what I have read on them... someone correct me if I'm wrong?
Ah right, that's why it has special oil then... Umm you'll need a way of keeping th eoil out of the end airflow for airbrushing then... that's very odd, I wonder if they could be used a low power hydraulic pump, lubricated and no worries, I may need a small pump for a massive art project using scrap parts including several large hydraulic rams which could in theory make it move but it's all just sketches now...
Rectifier (author)  killerjackalope6 years ago
It's possible they could pump hydraulic fluid, but I don't find it very likely.

My guess is that they would choke on anything that was not compressible, as I believe that is what kills fridges if you turn them on right after moving (the oil ends up filling the cylinder completely, locking up the piston and cooking the motor), though, again, I'm not sure on this. Also, they push pretty low volume - for airbrushing, it would require a decent size reservoir tank (I have a scrap CO2 tank that I plan to use for this).

To keep the oil out of the airflow to the brush, generally I've read suggestions just to make it flow through a relatively tall chamber - most of the oil drops out due to its weight, and then later flows back into the compressor when it is turned off (thus replenishing its oil supply. what weird things these compressors are?). Then, an inline filter gets the rest before it enters the reservoir tank.

Airbrush is a later plan and not really my priority - first I want to set it up as a vacuum pump with a settling tank inline and use it to do vacuum desoldering. I salvage a lot of parts from scrap, and power vacuum desoldering looks 100% awesome and appears to be a far superior way of removing ICs!
i want to know is it possible to use refrigerator compressor for airbrushing or not? and does the oil mixed with air ?
Sounds like a really good project...
Although I was aware of the fact that the oil used was "different" somehow, I am not really that familiar with these types of compressors.

However, this article referenced at this link, may help some.

Sorry I haven't been of much help.
Your link looks like it was hi-jacked by the illegal Turks.
What's up with that? ?
Rectifier (author)  Goodhart6 years ago
You've been of much help! That link was great! It explains so much about the workings of the thing! Anyone interested in fridge compressors, I recommend reading the above link, showing a disassembled compressor. It appears the oil gets in the air because it's sprayed liberally around the inside of the housing, and the air is drawn from the inside of the housing. As such, atomized oil gets picked up by the piston and pumped out the outlet. Also, if there is freon in the compressor, and you hold it upside down, all the oil will be driven out the inlet pipe by the pressure. Oops. I also see why it must be an oil that won't outgas badly under vacuum, as the whole motor is under vacuum. However, it appears an ordinary light mineral oil should do the job of basic lubrication fine, and shouldn't break down badly unless it gets too hot (or really dislikes vacuum) And it's now obvious that it cannot pump fluids! The whole engine would bog down under the viscosity. I'm not quite sure why they are so quiet, though. Must be because they run in a partial vacuum.
Sandisk1duo5 years ago
the lowest friction one..... that would be the obvious choice
I don't know if a fridge compressor is different but we just chucked light engine oil in our big compressor from time to time, even hydraulic in a pinch and it's thirty days older than me, well the pump is, the engine was swapped when the exhaust detonated due to age, then fell off on the way round so the new silencer was a bit of pipe welded directly to the manifold... My guess would be that two stroke wouldn't murder it but it may be a little heavy, I don't know much about fridge compressors as I said, however it may need a few repairs if the oil's coming out like that, it should be trapped inside it. Assuming it's piston based that is...
Hi guys, I converted a fridge compressor to supply air to my fish tank. I cut off the top of the case and ran a pipe dow the usual air inlet and straight into the actual pump inlet, this stopped any oil entering the air entering the tank. I use sewing machine oil in the pump as lubrication.
Hi dudes. I use a fridge compressor to power airstones in my 300ltr aquarium. I found the same way as you that the air intake comes from inside the sealed case and didn't fancy any oil getting into the air going into my tank My solution was to cut off the top of the case and have a pvc pipe fed down the usual air intake and straight into the air inlet of the pump itself. This setup bypasses any oil and then I added an inline air filter just to be sure. Running without any back pressure, the pump draws about 0.6 amps and 66 watts, but this of course rises as soon as there is any back pressure in the outlet pipe.
skunkbait6 years ago
I'd think ATF, power steering fluid, or hydraulic fluid.
Rectifier (author) 6 years ago
Oh yeah for the record, I went with ATF and it runs great on it. The only problem is the exhaust stinks of ATF. Ecch. I have to exhaust it outside or it will stink up the place. It's even worse because the vacuum pulls even more odor out of the ATF than usual, concentrating it to a sickly sweet cherry smell. If I do another one I'll be using a light mineral oil with a low vapor pressure, so I can run it indoors. It appears the lubricant doesn't matter that much as long as it is non-foaming, non-conductive, and light enough to be sucked up by the hollow crankshaft.
Rishnai6 years ago
I couldn't help you with your oil problem, but I sure learned a lot in the process of discovering that I couldn't help! Good luck with your project.
NachoMahma6 years ago
. Part of the reason that a special oil is required is that there is a partial vacuum in the compressor and one needs a lubricant that won't lose the more volatile components. It also requires a lube that won't be affected by the refrigerant. . I'd stick with lube designed and labeled for A/C compressor use. You can usually find it at automotive, hardware, and larger department stores. It often comes in the same size/shape ~1# can as refrigerant, so you can use the same equipment.
And the R-12 looks to be fairly common, too.