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Finally Got a Fridge Compressor (Need Help Setting Up)

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Finally Got a Fridge Compressor (Need Help Setting Up)

Unread postAuthor: BeaverRat » Sat Sep 04, 2010 9:34 pm

Well, today I managed to find a fridge compressor in a medium sized fridge. I was just curious how I am supposed to wire it up. Here are some pics:

There were only 3 wires entering the compressor, 2 wires (blue and black) to the side of the compressor, and one wire (green) bolted to the frame. I would assume that green is ground, black is -120 volts, and blue is neutral. How should I hook them up? I did not see any starting capaciters or relays. Just those 3 wires that entered the inside of the fridge compartment by the top. I just cut them near the hole, and unbolted the compressor.

Thanks
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Unread postAuthor: Technician1002 » Sun Sep 05, 2010 2:15 am

Your assumption is correct. The phase shift for starting is taken care of by the starting relay which is the lump that the blue and black wires attach to. Underneath the lump (it unplugs from the compressor) is 3 terminals that goes through the steel shell. The 3 terminals are Common, Start, and Run. The frame safety ground is the green wire.

The US and EU colors can be seen here;
http://www.regiscoyne.com/tech/pwrcordcc/
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Unread postAuthor: BeaverRat » Sun Sep 05, 2010 10:57 am

So are there two windings on the compressor? One for starting it up and one for running it? That little lump will take care of diverting the AC power from the startup coil to the running coil after the compressor has started?
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Unread postAuthor: Technician1002 » Sun Sep 05, 2010 11:10 am

Yes, that lump is the starting relay. When stalled (not running) the run coil draws high current which pulls in the relay and connects the start winding too. When the compressor comes up to speed, the run current drops (start current is still high) and the relay drops out leaving power on just the run winding.

This external relay eliminates the internal centrifical switch on normal single phase induction motors such as found on sump pumps, bench grinders, drill presses, table saws and such.

The spark of an internal switch would damage the freon with each operation eventually destroying the freon. Placing the relay external allows the relay to be replaced when it fails and reduces the probability of a failure inside the sealed case.

Here is a photo of one that has the winding exposed.
Image
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Unread postAuthor: BeaverRat » Sun Sep 05, 2010 11:43 am

Thank you,
So I am also wondering, why do some of the bigger ones have large capacitors and such? It appears mine was very easy to setup, because I connected those wires to a outlet plug, and it worked perfectly. I also discovered that the inlet is actually the larger of the three tubes. The outlet is the smallest diameter tube (1/8th inch I believe).

Now that I have it working, I have to complete the plumbing. I am going to use a compression fitting on the output that will give me 1/4th NPT male. Then I will have a brass tee, with a high pressure gauge and hose attached. I will be left with a 1/4th NPT male connector off of the hose. My question is, How should I go about filling the chamber? Should I use a schrader, quick disconnect?

Thanks again
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Unread postAuthor: Technician1002 » Sun Sep 05, 2010 12:14 pm

Small refrigerators use a capillary tube for the expansion valve. When the compressor shuts off, the pressure equalizes through the system so the next time the compressor starts, it does not start against a high pressure load. Low torque is all that is needed to get them up to speed.

An air conditioner or heat pump uses a thermostatic expansion valve and the thermostat may kick the compressor on when it was off for a very short time, so the compressor may be trying to start under a high pressure load. This requires high torque. The capacitor (if a single) is placed in series with the start winding to provide a current phase shift. This allows high rotational torque at stall or low speed to start the compressor under load.

Some high load systems also include a "Run" capacitor in additon to the start capacitor. It is a smaller value than the start cap and it remains providing lower run current into the start winding after the compressor is started and the high start current from the start capacitor is removed.

For further reading on the subject, the bible on refrigeration is this book.
http://www.amazon.com/Modern-Refrigeration-Conditioning-Andrew-Althouse/dp/1590702808
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Unread postAuthor: POLAND_SPUD » Sun Sep 05, 2010 12:14 pm

Don't forget to add another T with a BV for venting
In the past I used QCs but now I prefer polyamide tubing and push to connect fittings

Some people use QCs for hydraulic lines - they are pretty good AFAIK but a bit pricey
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Unread postAuthor: BeaverRat » Sun Sep 05, 2010 2:13 pm

If I used quick disconnect fittings, wouldn't the pressure just drain out of the chamber when I turned the ball valve? Is it impossible to disconnect them with 400PSI in the line?
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Unread postAuthor: c11man » Sun Sep 05, 2010 2:16 pm

i use hydraulic quick disconnect fittings on all my high pressure stuff. the male ends do have a check vavlve in them unlike normal shop compressor ones so that is nice. but about 400psi they are hard to remove under pressure and at about 500psi they are impossible to get off. so i either but a ball valve or a check valve on the male side so that i can vent the line before disconnecting the hose
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Unread postAuthor: BeaverRat » Sun Sep 05, 2010 4:13 pm

Can normal quick disconnect fittings handle 500 PSI, or do I need to buy hydraulic ones? If they are strong enough, I will just attach a ball valve to the male side on the gun and use that to seal the chamber so I can release the hose pressure.
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Unread postAuthor: POLAND_SPUD » Sun Sep 05, 2010 5:07 pm

there are pneumatic QCs that can handle 500psi and more but they are hard to find

It's not the best idea to use standard QCs at pressures close to and higher than, let say 500 psi... some of them can disconnect violently... lol and trust me that's scary - especially with a piston valve

hydraulic QCs are more robust and they are rated to 3000 psi so they should work fine... unfortunatelly they are also the most expensive option

ohh AFAIK screw on shrader adapters are not that bad so they are also an option



Personally I prefer push to connect fittings and tubing rated to over 50 bar... I've never had any problems with them (other than low flow - but that's not a problem on single shot guns... anyway you can buy 6x4 tubing which should completely eliminate this problem).
They are lighter than any other air hose, relatively cheap (let say 0.5$ per metre). There is no way I am going to get back to pneuamtic QCs.

Unfortunately you might have some problems with finding them in HP version. The stuff that's normally used in pneumatics is usually rated to 10-18 bar
yeah I ma probably going to mention push to connect fittings and tubing at least twice in this thread : )
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Unread postAuthor: wyz2285 » Sun Sep 05, 2010 6:00 pm

Nice fridge compressor you got there :) .one question, how much pressure can a normal fridge compressor produce?
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Unread postAuthor: BeaverRat » Sun Sep 05, 2010 6:06 pm

Oh, I see... You have a push to connect pipe adapter fitting with a check valve or ball valve on the gun itself, and the high pressure tubing with a drain valve on the compressor. To fill, you push in the tubing and start the compressor. To disconnect, you close the ball valve (if you don't have a check valve) and shut off the compressor. Then you drain the tubing, and disconnect it.

Am I correct?
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Unread postAuthor: POLAND_SPUD » Sun Sep 05, 2010 6:51 pm

yeah, but I use 3 way valves so I don't have to disconnect the gun (or turn the compressor off) as the valve closes off air supply and vents the pilot side at the same time...

I've got 15 meters of the tubing and it is really really light so it's not that I even notice that there is a direct link between the compressor and the gun.
It's not that I have to be hooked up to the compressor - I've got a portable 4L HPA tank too - but I've only used it once when testing the setup

But you are right, I use a BV to vent the the whole system after I am done. Well, not exactly the whole system - I have another BV between the compressor and the main tank so I can close it and vent the output side without venting the main tank... This means that the next day I don't have to wait - I've got plenty of air in the tank


Of course you can use the same method you described
To disconnect, you close the ball valve (if you don't have a check valve) and shut off the compressor. Then you drain the tubing, and disconnect it.

but once you've got an air reservoir it seems so wasteful...
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Unread postAuthor: BeaverRat » Sun Sep 05, 2010 10:38 pm

How did you find a high pressure push to connect fitting? This is the highest pressure one I could find (300 PSI)

Mcmaster: 51025K241
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