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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?

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markz3715 days ago

well if i were you i would go to homedepot or crappy tire in my case because i live in ca. and get compressor oil and if its a small skinny compressor then i would put in 120g (grams by weight{not oil wheight but the heavyness})and those fatter ones like on fridges then put 150-175g of oil through the suction but put a hoze on the discharge tocollect any oil that starts spewing out and in that case stop sucking up oil and let run for 10-20 munites un disturbed. your welcome and i expect a reply if it works!

Problem still is that the compressor needs the refrigerant to cool the motor, windings and actuall pump parts of the thing.
You can only run them for about an hour until they get seriuosly hot.
Just oil won't cut it, you need to add active cooling on the outside and even with that the inside will get boiling hot soon.
So in any case the runtimes should be checked as well as the oprating temp and if in doubt a temp cut off added.

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
Goodhart8 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)  Goodhart8 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)  killerjackalope8 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...
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