Automobile Air Conditioning Compressor

FlaAlchemist · Mon May 02, 2005 12:43 am

Does anyone know if a automoble air conditioning compressor can be converted to a vacuum source?
Idea

thenewrunne · Chemically Balanced

Yes, this has been done before. But be careful of:

1) It may run too hot and burn-out.
2) It may need oil coolant (depending on model)
3) It may not pull a consistant vacuum (it will probably be fine though)

ApprenticeCook · DILLIGAF

The also need a high torque electric motor to drive them (normally this is where the car engine comes in).

-AC

thenewrunne · Chemically Balanced

A better idea may be a fridge compressor. You can get new ones from fridge repair supply companies. That is what I used in the beginning, they pull massive vacuum the only problem I had was with heat generation (but a fan blowing over it was enough to keep it reasonable).

brixtonj · Tue May 03, 2005 1:56 am

Yep, It will definitely work flawlessly .

No , It won't heat up, as -its designed to compress air *which in itself generates lots of heat- and doing it in an very hot engine-bay with no overheating failure.

You need a serious electric motor to move this thing , probbably a 2 HP one. You need to feed also 12 volts to the electric clutch .Otherwise the pulley will spin without moving the compressor itself (as when in a car , the AC switch is in off , that the compressor is not operating , and the pulley is slipping).

Re:Lubrication :

Well , at least there are 3 types which are of the independent oil reservoir kind . These are the (US) York , the (EU) Sanden and the (JP ) Saniko. These are proven that they wont mix the oil with the air (and in any case .that's irrelevant) . How do I know that ? 'cos there's now a trend to use these AC compressors as engine-driven air compressors for pumping up tyres , power tools , for 4Wds ,, etc... Just google about "On Board Air" and you will get tons of info about using automotive AC compressors as air/vacuum pumps.

How much vacuum would IT pump ? LOTS . That's for sure . I am using a workshop-type Air Compressor , of an approximate displacement , and so far ,the results are impressive.

A Fridge compressor will make up as that much vacuum , but It has not the capacity to hold-it . I mean , anything can create decent vacuum, . The difficult part is to keep that vacuum when vapours are gennerated . I mean , "swallow" all these gases (refluxes , vapours , etc) and still KEEP that vacuum to 29.9. For that , you need a large , efficient , and powerfull vacuum pump.

If I had a AC compressor , and need a vacuum pump , Id definitely give it a go.

->Sorry for my clunky English<-

BrixtonJ.

bio · Working Bee

This might be a little overkill unless you already have all the parts or need to distill at high thruputs with a 50L flask.

Interesting website, I might add. These compressors will probably handle a lot of vapors if not too corrosive.

But hey, If you need to buy the motor it makes more sense to get a 1/4HP water pump rated about 2-3LPM at 20-30M head with a N......ene poly aspirator for a few bucks. Placed in a plastic 3 gallon cooler it will easily pull 10mm Hg with cold water and keeps up with a 6liter rig w/ 2 traps and column.. A 1 inch hose draped over the side to the suction means no holes to drill either. Put a slot in the cover for the suction line and aspirator to minimize splashing and noise.

If jugs of ice are frozen solid only about half a gallon of water is needed and they can be changed on the fly. Beats ice cubes all to hell. For 20mm just use a tap water feed that overflows to drain to keep a steady temperature. One of these around here sometimes runs for days at a time with no fuss no muss and NO FUMES.

drayen · Fri Aug 26, 2005 6:20 pm

oddly enough i've been dreaming about clendestine uses for air conditioning units, and i see a post on it...
anyhoo.....
this is a slightly different twist on the idea of using an A/C unit as a vacuum pump, but this would also have the added benefit of producing a very effective cold bath.
(this is just what i have thought in my head, pure theory. so if anyone's tried this, lemmie know)

what if one were to acquire and modify a home air conditioning unit,
so that the cooling coils were to sit in an insulated cooler.
add a pump, aspirator, and a length of hose from the outlet to recirculate the water.
i'm thinking this would be an excellent way to keep your water as cold as possible for aspiration purposes.
Also, a 2nd unit could be used to keep an antifreeze(or acetone) cold bath at a temperature that ensures things like anhydrious ammonia doesn't get above it's boiling point.

thoughts on this dream?

lusitania · Mon Sep 19, 2005 1:18 pm

Yes its actually very possible. You should search "phase change cooling +computer modding" or some shit like that. I was into this stuff before ever discovering my love of chemistry and its very feasible. It would be expensive to run a chilled aspirator because the cost to produce something like that would rival a decent vacuum and the device would easily be able to chill the water to something like -40C or so. For a bath it would be very easy. So lets say we're fabricating left to right here.

Compressor => Condenser (like a radiator AC) => Capillary tubing => Evaporator (simply copper tubing twisted however you want submerged in bath) => back to compressor.

simple loop. Could easily chill baths to -50C. haha finally an area of this site where i'm not a total newbee Smile

lol

bio · Working Bee

A dehumidifier was used to chill a giant cooler full of antifreeze to -20. The compressor was maybe 1/5HP and the spiral evaporator with coarse fins was placed in the liquid.
This is used as a vapor recovery unit and works very well but to keep up with an aspirator pump something much larger would be needed.

My aspirator pump setup needs maybe 2gallons of subcooled ice every 2-3 hours to keep the water below 5deg in an insulated 3gal igloo. So take the latent heat in 17lbs of ice as an indication of the btu's needed to be removed to size the compressor.

1ton=12000btuh
1kw=3414btuh

drayen · Sat Sep 24, 2005 4:56 am

mayhaps it could be used with ice as a way to avoid dumping ice in every 2-3hrs.
and mayhaps it'd be easier to adapt a household AC unit for cooling bath use.

bio · Working Bee

.......mayhaps it could be used with ice .............mayhaps it'd be easier to adapt a household AC unit for cooling bath use.......................

Ice has poor heat transfer compared to water but it could certainly be made to work. I freeze the ice in containers which are placed in the cooler and exchanged before totally melted. It is a pain in the ass for sure.

Window unit AC could be made to work as well however the evaporator coils are very large and the fins are very close. Something with a water cooled evaporator like a drinking fountain or even the flat plates from a small freezer would be much better.

One refrigeration Ton (12000btu)is about 1HP or say 1- 1.2KW actual used power.
This is the latent heat in a ton of ice. Forget the 770 some watts/hp as this is
theoretical assuming 100% efficiency.

So depending on all the other various factors my quess is that 5-8000 btu/hr should do the job with good insulation and a small effiicient aspirator pump of about 1/4 hp.

Check the sizing of the commercial units (lab chillers) for some ideas.

drayen · Mon Sep 26, 2005 4:39 am

blah....when i said ice i ment a saltwater+ice/antifreeze+ice bath
Razz

but anyhoo...

this would take a trip to the local home hardware store thingy.
but it shouldn't be too daunting of a task to carefully cut a bit back from where the cooling coils connect to the compressor, use something like a swedgelok fitting to give yourself enough tube that you can have the AC unit out of the way, but the coils fully immersed in the cooling solution.

the only difficult part of this task that i can fathom.
is that to disconnect the coils, it would require a draining of the refrigerent. and the the addition of (possibly?) more refridgerent when you add the extensions because the total volume of the system has been increased from the factory volume.

hahas · Mon Sep 26, 2005 6:37 am

if salt is involved, so is the possibility of corrosion, on untreated surfaces.

cutting tubing, flaring or swaging, yes, this is easy. but a strong vacuum needs to be pulled afterwards, or else you will find that air and moisture in the system is not a good thing.

perhaps it would be easiest to use a home chest freezer (a little big), or a 0.5 m3 supermarket open-top freezer if these are as common where you are as they are here.

if not using a system designed to produce low temps, you may have a hard time getting them without adjusting the metering device or removing some of the charge.

bio · Working Bee

......if not using a system designed to produce low temps..........

AC units are designed for a 45deg F evaporating temp and if operated very far below this the capacity falls off drasticaly and the compressor will overheat as the compression ratio rises. Capacity curves are readily available from the manufacturers.

Metering device is almost always a capillary tube in cheap AC units. They are not adjustable and will not work if the pressure differential varies much from the design.

If you expect the thing to last more than a few hours and don't have refrigeration experience with the proper tools then about the only SIMPLE thing to do is procure a
refrigerator/freezer unit (full size). These have enough tubing from the compressor to the freezer plate evaporator so that the gas circuit could be undisturbed when dissmantled and placed in the cooler box. The older ones have only a flat plate that cools both compartments. Forget a forced fan coil as not enough surface are and the aluminum fins will corrode away in short order so epoxy paint the plate.