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Re: Fridge compressor for vacuum pump?
Tesla List wrote:
> Original Poster: Alex Crow <user-at-alexcrow.clara-dot-net>
>
> Dear All
>
> I just managed to rip out a compressor from an old freezer (doing my bit
> for the ozone layer in the process!) and was wondering which bit sucked
> and which blows - the big pipe at the top which went into the freezer or
> the one at the back that went to the radiator?
The big 'un sucks and the small one blows. :-) You'll probably also have
another fitting that is silver-soldered shut. that is called the process
fitting and is also connnected to the suction side. Be aware that the
suction empties into the can and so any trash will contaminate the oil.
> It's also got three mains
> wires, but I haven't opened the junction box yet so maybe I'll work it
> out then.
if one wire is green, then you have power, neutral and ground. A starting
relay will be under the cover. If all the wires are black or if there are
colors like red, yellow, orange and such, then the compressor needs an
external start relay. You should have gotten that with the compressor. the
three wires are common, run winding, start winding. The start winding will
be the higher resistance. the starting relay momentarily connects the line
to the start relay until the starting current drops enough for the relay to
drop out. the run winding connects to the line. Start relays are cheap,
only $5 or so but if you don't have one and don't want the hassle of getting
one, you can start the compressor manually by applying power between the
neutral and run winding and then momemtarily connecting the start winding to
the run winding. Do it no more than 10 or 15 seconds or the start winding
will be burned out.
Some compressors use a cap to start and/or run but they are rare on
consumer-grade freezers.
> Anyone used these as a vacuum pump before? what sort of performance can
> I expect?
Yes. You will get quite excellent results. Not as good as a real 2 stage
sliding vane pump but more than enough for vacuum impregnating. For even
better results run 2 in series. You'll get some oil mist out the discharge
so you'll need to trap the oil and return it to the compressor via the
inlet. Commercial oil traps are available or you can make one from a
section of 1" pipe arranged vertically and loosely filled with steel wool.
this is a coalescing filter. it will be easiest to just collect the oil,
toss it and replenish a similar amount through the suction line.
If you use it as a compressor, be aware that it will probably not be able to
start under pressure. Bleed off the pressure side before attempting to
start.
John
--
John De Armond
johngd-at-bellsouth-dot-net
Neon John's Custom Neon
"Bendin' Glass 'n Passin' Gas"