Air compressor from a fridge compressor

[Bainford]

Has anyone tried to build an air compressor for painting, using the compressor from a refrigerator?  If so, did you experience any oil presence in the output air?

[Pete J.]

Good question and I don't know the answer.  I do know that every compressor that is designed for refrigerants will have some form of lubricant. Either mineral oil(R12) or a synthetic(R134). Not sure that they can run without it and if it got in your paint it could cause a problem. Without it, I can't imagine the compressor would last long. 

[disabled modeler]

Id expect they would put oil..etc. into the air.  I have used them to vac out AC systems for repairs and charging them.

[Bainford]

Yeah, it looks like a problem, and I can't imagine a separator being sufficiently effective at removing oil from the air to permit painting. However, I have been hearing of people making quiet compressors for painting from fridge compressors, but can't imagine how they deal with the oil output. Actually, I don't have a good idea of how much oil would end up being released in the first place, but I imagine there would be some, and any would be too much if it can't be effectively removed.

[cowboy rich]

Hey my line of work! A refrigeration compressor is designed to pump out a small amount of it's in to the closed loop to keep everything lubed so yes you will get oil that would normally return to the compressor.

[Bainford]

Cheers Rich!

[robdebie]

On 4/30/2018 at 8:22 PM, Bainford said:

Has anyone tried to build an air compressor for painting, using the compressor from a refrigerator?  If so, did you experience any oil presence in the output air?

Way back I ran a fridge compressor that had most of the oil poured out. Not very smart with regards to lubrication, but it worked well enough, for many years :-) Later, when I sawed the 'lid' off,  I found out it heated up very fast, mostly because of the air compression. That created a smell of burned oil in the output air. I also ran it without the flap valves, and it did not heat up in that configuration.

I now have a Sil-Air 20 quiet compressor hat basically also uses a fridge compressor. I'm pretty sure it 'inhales' its air from inside the black steel casing, where the oil is splashing around due to the electric motor turning in it. So yes, there's oil in the output. That also becomes clear when you drain the small air tank: what comes out is a smelly combination of water and oil. Of course there's a water/oil trap included in the pressure regulator, but frankly I don't think it works that well. Still, I don't experience problems that I would link to oil contamination.

Rob

Edited May 29, 2018 by robdebie

[Ace-Garageguy]

Even the large compressors we use in real-car body and paint shops are lubricated internally, and introduce a small amount of oil into the compressed air. A GOOD oil separator / filter is essential, along with a water trap, located far enough from the compressor so that the air cools and contaminants tend to condense out of the air prior to going through the filters.

[robdebie]

1 hour ago, robdebie said:

I now have a Sil-Air 20 quiet compressor hat basically also uses a fridge compressor.

Here's a view of my Sil-Air 20 opened up for oil replacement. Mine has a ring clamp for the 'lid' (that is not shown here), there are also versions where the lid is welded on, as is always the case in fridge compressors.

You can see the vertical crankshaft poking out at the top, the cilinder is horizontal to the left. The cilinder head has a lighter color. The electric motor is down below. The oil level is about 20% of the height of the the casing. I'm pretty sure the electric motor splashes it around quite vigorously.

The air enters the black casing through the pipe on the left, that has a air filter at the end. It also serves as the oil filling point, as indicated by the label. The air exits the pump through the long brass pipe at the top. Its length allows the motor to move around, since it is hung in springs.

Hiding behind the plastic refill oil container is the rectangular steel air tank, and to the right is the pressure regulator with oil/water seperator below it.

Rob

[Bainford]

4 hours ago, robdebie said:

Way back I ran a fridge compressor that had most of the oil poured out. Not very smart with regards to lubrication, but it worked well enough, for many years :-) Later, when I sawed the 'lid' off,  I found out it heated up very fast, mostly because of the air compression. That created a smell of burned oil in the output air. I also ran it without the flap valves, and it did not heat up in that configuration.

I now have a Sil-Air 20 quiet compressor hat basically also uses a fridge compressor. I'm pretty sure it 'inhales' its air from inside the black steel casing, where the oil is splashing around due to the electric motor turning in it. So yes, there's oil in the output. That also becomes clear when you drain the small air tank: what comes out is a smelly combination of water and oil. Of course there's a water/oil trap included in the pressure regulator, but frankly I don't think it works that well. Still, I don't experience problems that I would link to oil contamination.

Rob

Thank you, sir. Very helpful information.

[Can-Con]

Here's a pic of my old "Frankenstein" compressor. I got it third hand and used it for almost 15 years. I don't know how long it existed before I got it but I do know it was built by a Canadian Armed Forces helicopter mechanic. That little air switch  on the left is to dump excess air pressure. I's the windshield wiper switch form something, some sort of APC, IIRC. The silver thing behind the pressure gauge was a moisture trap. I've had to clean the oil out of it a couple times over the years but it was no big deal. And an old air tank for storage. Only thing it didn't have was an automatic pressure switch. I had a Christmas tree light remote control hooked to it to turn it on and off.  I've had it run up to around 80 or 90 PSi before a hose blew off. 

I kept it hid back in a corner under some boxes etc with just the gauge sticking out.  Didn't get cleaned back there very often.