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perdu

fridge motor compressor question

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I have a fridge motor compressor which a friend gave me a year or two ago

 

When I start it up it runs for a few seconds then stops, air bleeds through if I have the brush trigger open then after a short 'intermission' it starts up and doesn't do it again during the session

 

But in use it smells very industrial and sometimes the usual liquids need bleeding out of the trap/regulator

 

Can the oil be causing this and if so can I service the oil levels?

 

I didn't see how it was extracted from the old fridge so I'm wondering if the smell is liquified refrigerant and oil mixed 

 

The compressor seems to work very well and can give decent pressure if I play with the regulator, just these admittedly minor niggles

 

If anyone can advise I'd be grateful

 

Bill

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Hi Bill

I have a Revell Omega compressor, which uses the same sort of compressor but specifically set up for airbrushing

2 hours ago, perdu said:

When I start it up it runs for a few seconds then stops, air bleeds through if I have the brush trigger open then after a short 'intermission' it starts up and doesn't do it again during the session

Don't know what's happening here, rather depends on what control circuits are being used for the compressor

 

2 hours ago, perdu said:

But in use it smells very industrial and sometimes the usual liquids need bleeding out of the trap/regulator

 

Can the oil be causing this and if so can I service the oil levels?

Yes and maybe

 

My compressor uses a small amount of oil, carried over into the air tank which needs draining off periodically together with the condensate. As it uses oil it needs topping up occasionally as well, mine has a filling tube and a sight glass level gauge (which I guess yours doesn't have?)

 

2 hours ago, perdu said:

I didn't see how it was extracted from the old fridge so I'm wondering if the smell is liquified refrigerant and oil mixed

I doubt very much there'd be any refrigerant left in the compressor after a short while in use, however the smell is most likely related to the oil.

 

Most refrigerant oils are hygroscopic (absorb water), not a problem in a sealed refrigerating system, but not good in an open compressor. If the oil in the compressor is the original oil from when it was recycled from the fridge, then given it's use it's probably well past it's sell by date and the smell is likely the oil breaking down and wear from compressor parts if it's not doing it's job properly.

 

If you can work out a way of getting the oil out and refilling it to a working level I'd recommend draining it, refilling with a good quality synthetic compressor oil, running it off load (vent to atmosphere) for 10 minutes or so, then draining and refilling again. Flushing (filling twice) will get rid of most of the contaminants inside the compressor and will ensure there's no compatibility problems between the old and new oil.

 

Here's what it probably looks like inside:-

compressor.jpg

There's lots of stuff on google and youtube on abusing old fridge compressors.

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Thank you for that Dave I've never seen the insides of one before

 

I know maybe I ought to generate some googlefu to look into these things 

 

My compressor has an in and out pipe, considering there's another one soldered up I suppose that will be the oil fill method so I might doo the doo with Google to see if I can check it out and find a drain hole

 

Off we go to the net, cheers again Dave

 

Taught me what I needed to know,

 

B

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Bill, the 3rd pipe will be for freon filling from when it was in a fridge.

If there's a reasonable length, you could cut the end off this (lclose to the end as possible, you just want to open it up) Then tilt the compressor so that either this or the suction pipe connection is on the bottom, you should be able to drain it from there, the filling and suction should go into the same space, oil out of one, air in the other. Drain it into a container so you can get an idea of how much is in it eg old plastic mik bottle. If this works, you can put it right way up and fill through the filling tube at least as much as came out, best plus a bit more (20-30%?). I use a large bore syringe for this. My filling tube has a rubber cap on it, doesn't need to be pressure tight, just to keep dirt out

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Posted (edited)

Right I get that (even though I'm a bit slow I'm getting the hang of that) so if I open that and drain through that I can simply put a rubber bung afterwards

 

What oil do I use? I see mention in here of even Castrol GTX, surely that can't be right

 

 

Oooh Kay, like a proper dope I didn't look in your post above

 

Proper hi quality compressor oil, Machine Mart?

Edited by perdu

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42 minutes ago, perdu said:

Right I get that (even though I'm a bit slow I'm getting the hang of that) so if I open that and drain through that I can simply put a rubber bung afterwards

Yes. You need to open this to let air in (if you drain it through the suction line) or to let the oil out (and the air goes in the suction line) which ever is easier to use as the drain.

45 minutes ago, perdu said:

 

What oil do I use? I see mention in here of even Castrol GTX, surely that can't be right

It would be OK, better than fridge oil, but not as good as

 

45 minutes ago, perdu said:

Proper hi quality compressor oil, Machine Mart?

This is what I use

Rather depends on what you want to spend, if you've got some good engine oil in stock and want to see if this improves the compressor performance it certainly won't do it any harm. However if your compressor has the original fridge oil in it and the compressor is starting to wear out filling it with expensive compressor oil isn't going to cure it.

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You need to use a mineral oil for a compressor, ie compressor oil don't use car oil.Also when you use the compressor a little oil will always be carried out with the compressed air and caught in the water trap/filter, thats why you have to top up the oil depending on how often you use it in these types of compressors.

I wouldn't use it to spray directly to the airbrush without a filter/water trap as your air will be contaminated with oil else.

When they are connected to a refridgerator the system is a sealed unit so it never loses oil as it is carried around with the refridgerant and back into the compressor.

Also it's going to be a little hit or miss topping the oil up this way as you won't know how much to put in, too much and the compressor won't start.

The silent type compressors that use these motors normally have a little window in them with a mark so you know how full or empty the motor is.

 

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1 hour ago, colin said:

You need to use a mineral oil for a compressor, ie compressor oil don't use car oil.

Negative on that. You don't need to. You can, but synthetic oil is better. The compressor will run much cleaner and time between overhauls is significantly improved with synthetic oils (5-10 times longer), you don't get carbon build up on the discharge side like you do with mineral oil. A good quality car engine oil will work (an engine is just a compressor with added bang) but as always an oil specifically designed for the job will be much better.

 

1 hour ago, colin said:

Also when you use the compressor a little oil will always be carried out with the compressed air and caught in the water trap/filter, thats why you have to top up the oil depending on how often you use it in these types of compressors.

I wouldn't use it to spray directly to the airbrush without a filter/water trap as your air will be contaminated with oil else.

When they are connected to a refridgerator the system is a sealed unit so it never loses oil as it is carried around with the refridgerant and back into the compressor.

Also it's going to be a little hit or miss topping the oil up this way as you won't know how much to put in, too much and the compressor won't start.

Agreed, that's why I recommended Bil measure the quantity he drained out to get an idea of the minimum capacity

 

1 hour ago, colin said:

The silent type compressors that use these motors normally have a little window in them with a mark so you know how full or empty the motor is.

Yes, mine has a small sight glass, however adding one to Bill's compressor without causing it damage could be more hassle than it's worth

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It's probabley lost oil from using it this way so tipping out whats in there won't really help, 30yrs doing refridgeration and putting oil in vac pumps which we use to vaccum out the refridgeration systems which are basically a compressor and I've never been advised by anyone to replace the oil with car engine oil as it will do, I just go buy what the manufactuers advise. And I don't think I advised him to drill and put a sight glass in the compressor

Also not sure how you get carbon deposits on the discharge side from a electric brushless motor, unless it had burnt out

But then what do I know a ;)

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I intend getting the oil from Machine Mart is that the proper stuff?

 

I don't know any fridge repair guys round here

 

I really appreciate you two helping me with this, I hadn't given any thought to how my compressor actually worked so I think I'll stop calling myself a mechanic or engineer from now on

 

Shamed I am. :(

 

But seriously I will get the oil then try to empty and refill it over the weekend

 

Cheers guys

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Hi Colin, sorry if I ruffled your feathers, it wasn't intended.

 

My background is 35+ years as a marine engineer, the last 10 as Chief Engineer on large container ships. These carry a significant quantity of refrigerated cargo, I did 3 years as engineer operating the reefer plant (5 compressors as big as a small family car) and I'm still overall responsible for the maintenance of the reefer systems. I've also maintained and operated air compressors of all types and sizes and engines up to 100,000hp.

When I first went to sea air compressors were invariably lubricated with mineral oils, and required regular maintenance (200-500hrs) which included stripping and cleaning the discharge valves to remove the coke from carried over and burnt oil. With modern synthetic oils this is now usually a check/quick clean at 1500-2000 hrs.

Vacuum pumps use a special oil with a very low vapour pressure to enable them to pull very high vacuum levels. They will run fine on other oils, but won't achieve full vacuum. I've personally had a large reefer system under vacuum for a month to remove water after a condenser failure. Initially I was changing the oil every 30 minutes due to the level of water contamination being extracted from the system. Ordinary cheap compressor oil was used because a) vacuum pump oil is relatively expensive and b. we had limited stocks of vacuum pump oil on board, but we had hundreds of litre of compressor oil. I only switched to vacuum pump oil when I wasn't having to change the oil every day to pull the system down below 4 torr. That vacuum pump (Robinair) continued to give many years service afterwards.

Modern car engine oils, eaven the cheaper ones, are quality refined products and are available in a viscosity range similar to compressor oils. They have additives to deal with combustion products and to withstand the higher temps found in an engine, but these wouldn't be detrimental to a compressor.

Refrigeration oil is hygroscopic (attracts water) so cannot be used outside a sealed system without detriment to the oil and equipment in the long run.

 

So, Bill has an old fridge compressor that has been adapted to power an air brush, he's aquired it for very little outlay and has run it for several years. His initial post leads me to believe the oil is deteriorating (smell) and is running low (he hasn't topped it up, and reduced oil quantity will lead to overheating and oil deterioration).

The oil recommended by the manufacturer will have been a refrigeration oil, which as above is no longer suitable due to the change in duty of the compressor.

To avoid and compatiility problems beween the old and new oil I recommended flushing the compressor, 2 changes of oil = ££££.

For my Revell Omega (similar to Bill's but new built/purpose produced) a good quality synthetic oil is recommended, again ££££.

Like most of us of a certain age and who drive a car, we're likely to have  a can of engine oil in the garage, I have and I rather suspect Bill has. As this isn't going to incur any further cost, or do any further damage to the compressor, I suggested this as a replacement oil to see if the compressor performance improves.

With the limited use a compressor of this type gets, I'd also suggest that if it works, it will be fine for the remaining life of the compressor.

I wouldn't suggest using engine oil to top up a purpose designed compressor, I would recommend the same as the manufacturers, a 1 ltr can will last the lifetime of the compressor and is a small percentage of the cost of investing in a new compressor.

 

Regarding the oil level sight glass, I hadn't misunderstood your comment as an instruction/recommendation to fit one, I was merely pointing out that to attempt to do so on a compressor such as Bill's would most likely damage the compressor. If the above advice works and Bill wants to check the oil level in the future, it won't be too difficult once he's done it before, to drain the oil, check it's condition & quantity, and refill the compressor.

 

Hope this explains my reasoning for the above advice sufficiently

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Thanks for an excellent clarification Dave, I'll be having fun on Saturday

 

 

EEK

 

It seems that is tomorrow, retirement is a bugger

 

:)

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I opened up the compressor pipe and drained out the eggcupful of stinky oil

 

It seems logical to me that there'd be more oil in there than that but rather than bung a full pint in I have cautiously replaced about half a pint of semi synth

(All that was available)

 

I restarted the unit and it ran without stopping from the beginning and put out a few 'blerts' of oily vapour then began running a fine pressure

 

I cleared the filter bowl and tried a test spray of the new Sovereign RAFBlue Grey on the tail of my Wasp,

 

Everything seems so much better, though it hasn't killed all of the stink

 

I think I'll run awhile then redrain and see if the oil that comes out is less thick and gruesome

 

Thanks for your help with this

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Hopefully you've caught it in time, Bill. If its been running for a while with only the minimum oil in there, there's bound to be some residues that the new oil will flush out. Run for a while, drain and refill. Half pint seems about right for your average size fridge compressor, and semi synthetic will be fine.

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Posted (edited)

Hiya,I thought I ought to return (call me Zorro!) and let you know how I've got on since you helped me with the fridge motor compressor

 

After being still a bit stinky at first the smell has lessened to the extent that I'd even be prepared to use the airbrush without opening the doors to the outside world

 

It's in the garage next to the boss's domain, the cookhouse

 

The help you gave me means that now it starts up immediately, giving full pressure within a second or so and doesn't seem to get hot'n smelly at all now

 

So thanks for the help, that diagram of its innards was invaluable by the way

 

If I can see something I can usually deal with it

 

Falling meteorites don't count 😨

 

Cheers

Edited by perdu

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Isn't it amazing the expertise that exists on BM & that those who possess it share it so freely? Most excellent! I only ended up in here Bill as I appear to have misread the directions to the Cafeteria you posted in Fritag's 'ork  thread & I was fancying a fry up....!! 

 

Seriously I was looking for the thread you mentioned that said one could use a compresser to de-gas silicon moulds, but I haven't found it yet, do you have a link perchance? Intriqued me that has...

 

This thread has however reminded me that I haven't checked the oil in my compressor for, oh, a year or two...!! Must do so before it starts smelling...!! 

 

Keith

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You must have missed the door Keith, its just behind the entrance to the area selling ladies fine and fancy clobber

 

Maybe the over-strong smell of Charlie and Miss Dior hid the fine aroma of sos and beans heating up

 

As for the compressor bit, I can't find it either but I freely admit I was also trying concentrate on F1 from Sochi

 

I'm off far another delve now, catch you laters

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Found it

 

Down below a little bit

 

"Turning a compressor into a vacuum pump"

 

Includes helpful info from Nigel Heath amongst others

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Thanks Bill, I must have walked past that thread too, very distracting these ladies fine & fancy clobber places!

 

Had a read of the thread & I don't do enough casting to warrant spending the time (or any dosh) on modding my comperessor for it. Besides I'd likely blow it (& quite possibly the house) up when attempting it...!!

 

Ta again

 

Keith

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If I can pick up a cheap second hand old pressure cooker I intend giving it a go

 

Like you I'm not about to spend big dosh to cure a minor niggle

 

Not when I've got a couple of old electric toothbushes I can use as vibrating tables

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Just a minor update, six months in and very chuffed with the revitalised fridge motor

 

Thanks for your guidance

 

:thumbsup:

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