more newbie questions: compressors and ideas

[FoxTrottZero]

Just read chilly's awesome link to the SWEP manual thingy... very informative

Question: how does the compressor know when to shutoff? specifically on window airconditioners, but I imagine most others... I can tell that the thermostat regulates when to turn on the compressor... but why does it shutoff at a certain point? don't get me wrong... I'm glad it turns off! lol! BANG!
is it a pressure gauge or a timer or something?

Also... I've been looking through a Grainger Industrial Catalog and found these neat little brass fittings for flared copper pipe to convert the ends to threaded adapters... you guys've probably seen them and used them on shrader access valves... I'm thinking about using them to fit the pipes together- they're rated from 650 to 1400 psi... so it should hold up pretty darn well... look ma... No brazing! think about how quick a captube length change would be.
Any tips there?

I also have a HUGE industrial air compressor for my woodworking crap at home... thinking of converting the intake so that I can evacuate my loop with it.. ANyone ever seen or done it? there's a nice threaded pipe adapter on the intake, so I figure... why not? Probably get a full evacuation in less than two minutes with that ten-horse compressor sucking on the end of my evac line! Again... tips?

[FoxTrottZero]

one other thing...
I was a very lucky lad... found an almost new (busted thermostat -a lighter heating the temp bulb gets everything running, lol.) 10000 btu/hr wall-A/C at the dump with a beautiful tecumseh scroll compressor in it.
New to scroll compressors (new to everything mostly)
What's that bulb on the side of the compressor housing... i can see that it is an intake... but does it serve as a last-ditch filter/suction line accumulator or something?

I've definately caught this Phase Change-OC bug!

[craig588]

Window air conditioners use timers and temp probes to shut them off because people don't like cold temps. (R22, the most common gas used in A/Cs is cabable of doing -40C) The phase change systems we build never turn off the compressor while they are on.

I belive that a regular air compressor is "dirty", it will allow dust and other contaminants into the system, I'm not sure though.

I think the bulb you are talking about on the side of the compressor is the start capacitor. It is used to provide the amperage required to provide the huge amount of torque required to get it started.

You might also be talking about the drier. A drier is a filter that traps moisture before it is sent to the evaporator, freezes, and clogs up the system. It should be right before the cap tube.

[FoxTrottZero]

So the compressor never shuts off on your systems? how do you keep the high side from overpressurizing and damaging things? well... actually... as the loop cycles, I imagine that at some point, the pressure in the high side is high enough and the refrigerant in the low side sparse enough, that the system reaches some sort of equilibrium but still... pressures would scare the sh*t out of me.

As for my question about using an air compressor to evacuate my loop... it's sucking air! how could dirt infiltrate the lines if all the air is moving out of them?

and the bulb thing on my compressor can't be a capicitor... the low side enters through it... and there's a capacitor elsewhere in the A/C.
can't be a drier because it accepts the low side to the compressor... the drier is over by the evaporator and capillary tubing...

damn... what is this thing!?

[Scout255]

So the compressor never shuts off on your systems? how do you keep the high side from overpressurizing and damaging things? well... actually... as the loop cycles, I imagine that at some point, the pressure in the high side is high enough and the refrigerant in the low side sparse enough, that the system reaches some sort of equilibrium but still... pressures would scare the sh*t out of me.

Correct, the compressors never turn off. Once the high side has reached it's target pressure (10 bar lets say) it will ideally never increase unless something is seriously wrong. Then it goes through the metering device to the low side (i.e cap tube, txv), is evaporated, and then sucked in through the suction line.

I think your thinking of the refrigeration cycle a wee bit wrong from what I can see. It appears you think that the compressor just pumps refrigerant from a storage tank to the highside. Instead, gas is constantly recirculateing. Emagine a small element of gas moving completely through the system. It will first be drawen from the suction side and compressed to the high side pressure, be cooled to a liquid in the condensor, expanded and boiled off in the evaporator, then drawen in from the suction side to be compressed again. Their is no accumulation of gas or pressure on the high side once it's target pressure is reached.

As for my question about using an air compressor to evacuate my loop... it's sucking air! how could dirt infiltrate the lines if all the air is moving out of them?

I don't believe contamination would be a major problem because (as you said) no air enters the system. However, what would be a problem is using your compressor to evacuate the system to the correct vaccum. Most compressors are incapable of produceing the low 50-100 micron vaccum that most commercial airconditioning vaccum pumps are (this low vaccum is required to remove any water from the system). Depending on the quality of your compressor you *may* be able to use it as a vaccum pump, but you should DEFINATELY tripple evacuate the system and get an accurate vaccum gauge to tell what your compressor is capable of handleing.


and the bulb thing on my compressor can't be a capicitor... the low side enters through it... and there's a capacitor elsewhere in the A/C.
can't be a drier because it accepts the low side to the compressor... the drier is over by the evaporator and capillary tubing...

damn... what is this thing!?

Not sure exactly what your describeing, but perhapse it's an accumulator of some sort?

[FoxTrottZero]

thanks for the help scout... sorry to be misleading... Of course I know that the refrigerant runs in a loop! that's like the second thing you learn in refrigeration! I just imagined the refrigerant building and building up behind the metering device... silly.

[Scout255]

No worries, glad I could help :)

[gkiing]

By the way foxtrot you can't flare your system together, and if you did, have fun checking for leaks :)

You might want to look at the direct die guide on vr-zone.com, its in the stickies.