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I have an A/C compressor to convert. Questions.

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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I have an A/C compressor to convert. Questions.

Unread postAuthor: boyntonstu » Sun Jul 26, 2009 6:23 pm

I replaced an 8,000 BTU window A/C yesterday that had a good compressor but a faulty touch pad controller.


Today I removed the old compressor and I would like your input/advice.

How does a 25 cu ft refrigerator compressor compare to on from an 8,000 A/C compressor?

There is a starting capacitor. Use it or not needed?

Do I need to add any oil for lubrication or is there enough left behind from the Freon?

There is a small cylinder dryer. Keep or remove?

What fittings to use to transition from the copper lines to the filter and to the output hose?

What filter do you recommend?


Many thanks.

BoyntonStu
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Re: I have an A/C compressor to convert. Questions.

Unread postAuthor: Technician1002 » Sun Jul 26, 2009 7:16 pm

boyntonstu wrote:I replaced an 8,000 BTU window A/C yesterday that had a good compressor but a faulty touch pad controller.


Today I removed the old compressor and I would like your input/advice.

How does a 25 cu ft refrigerator compressor compare to on from an 8,000 A/C compressor?


The AC is much higher volume. It's made to cool a larger area. The power for the fridge is about 200-300 watts when running. The AC about 600-800. Big difference in capacity.

There is a starting capacitor. Use it or not needed?


You will need it to get it to start, along with the start relay. Wiring diagrams for the 3 pin compressors are online. A quick search brings them up.

Do I need to add any oil for lubrication or is there enough left behind from the Freon?


Usually the old lube is fine for several years. Don't tip over the compressor. Oil may run out the pipe.

There is a small cylinder dryer. Keep or remove?


Remove. It's the filter dryer to keep moisture in the system from freezing and plugging up in the freezer. Normal moisture in the air will plug the dryer filter up when the system is no longer sealed.

What fittings to use to transition from the copper lines to the filter and to the output hose?


Anything you wish that fits.. Silver brazing, Silver solder, Flare fittings, etc to fit the tubes.

What filter do you recommend?


Auto gas filters work fine as an air filter on the inlet to keep out dust.


Many thanks.


BoyntonStu


You are welcome.
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Unread postAuthor: mark.f » Sun Jul 26, 2009 7:50 pm

Kind of off-topic, but...

You completely replaced a 8,000 BTU window unit because of a touch-pad controller? :shock:

While a greater electronics buff than myself could fix it with parts lying around, I'm sure a replacement pad would be chips compared to a new unit, for people like you and me.

Also, a key reason I buy things with mechanical interfaces. :D
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Unread postAuthor: boyntonstu » Sun Jul 26, 2009 8:02 pm

mark.f wrote:Kind of off-topic, but...

You completely replaced a 8,000 BTU window unit because of a touch-pad controller? :shock:

While a greater electronics buff than myself could fix it with parts lying around, I'm sure a replacement pad would be chips compared to a new unit, for people like you and me.

Also, a key reason I buy things with mechanical interfaces. :D


A new touchpad is $94.

I Googled this GE model and there are a lot of problems with it.

When I opened it up the unit was completely corroded.

(We are 1 block from the Ocean.)

A new unit and 2 years instant service warranty was $185.

I wanted a mechanical/simple unit but they are twice the price and made in China.

There is no relay of any size.

I suppose that I'll need to buy one unless it it a run capacitor:

Two basic types are used in electric motor:

1) Run capacitors are rated in a range of 3-70 microfarad (mfd). Run capacitors are also rated by voltage classification. The voltage classifications are 370V and 440V. Capacitors with ratings above 70 microfarad (mfd) are starting capacitors. Run capacitors are designed for continuous duty, and are energized the entire time the motor is running. Single phase electric motors need a capacitor to energize a second phase winding. This is why sizing is so critical. If the wrong run capacitor is installed, the motor will not have an even magnetic field. This will cause the rotor to hesitate at those spots that are uneven. This hesitation will cause the motor to become noisy, increase energy consumption, cause performance to drop, and cause the motor to overheat.

2) Starting capacitors are housed in a black plastic case and have a mfd range as opposed to a specific mfd rating on run capacitors. Start capacitors (ratings of 70 microfared or higher) have three voltage classifications: 125V, 250V, and 330V. Examples would be a 35 mfd at 370V run capacitor and an 88-108 mfd at 250V start capacitor. Start capacitors increase motor starting torque and allow a motor to be cycled on and off rapidly. Start capacitors are designed for momentary use. Start capacitors stay energized long enough to rapidly bring the motor to 3/4 of full speed and are then taken out of the circuit.

I will determine which type it is tomorrow.

OTOH Perhaps a compressor with no load should start O.K. without a capacitor?

Edit: I just found this: http://highperformancehvac.com/capacitors.html

The dual run capacitor looks exactly like mine.

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Unread postAuthor: Technician1002 » Sun Jul 26, 2009 9:18 pm

Most motors with a run capacitor are low torque starting items such as fans. If the air conditioner has full electronic control (you mentioned it) then an off delay can be guaranteed so the system pressure equalizes while off. It can use just a run capicator.

Compressors with just a mechanical thermostat that may cycle back on before the high side pressure has bled off most often uses a start relay and cap. The start relay attaches directly to the side of the compressor. If the AC did not come with a start relay, it is most likely a run cap only style. These will not restart with any head pressure on the compressor. They will need to be bled completely down before re starting. They will stall and not start if you try to run them on a pressure switch in a normal air compressor setup.

It will need the cap of either a start or run cap to start up even with no load.
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Last edited by Technician1002 on Mon Jul 27, 2009 3:03 am, edited 1 time in total.
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Unread postAuthor: POLAND_SPUD » Mon Jul 27, 2009 1:26 am

Usually the old lube is fine for several years. Don't tip over the compressor. Oil may run out the pipe
it will leak out anyway overtime so you'd have to replace it
the exact amount you have to add is hard to determine so if you could get an oil filter it would be great... If you had one that separates oil and air and then let's you drain the oil then you could get a rough idea of how much oil you need to add

unfortunately, commercial ones are rated to 10 bar/145 psi so they are no good if you want to reach higher pressures... but you might copy their design and build one yourself... does anyone know how they are built ?? it doesn't have to be 99% efficient as some oil will lube your parts and prevent rusting



I use home-made compression fittings and they works ok at high pressures

they are built from two brass 1/2" male-female adapters. This type of compression fitting is very simple to build - several 1 or 2 rubber washers (with a hole big enough to put the copper tube through them) are sandwiched between the two adapters.

so you screw in one into the other the washers compress and they squeeze tightly around the tube...
you might need one or two steel washers to support the rubber washers but mine work all right without them


There is a starting capacitor. Use it or not needed?
I think you'll need one... does the compressor start up ?

as an air filter you can use car air filters.. they are dirt cheap and premade... some come with a nice plastic transparent casing and a length of tubing that oyu can easily attach to the air intake
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Unread postAuthor: boyntonstu » Wed Jul 29, 2009 1:37 pm

http://i348.photobucket.com/albums/q339 ... ressor.jpg

I connected the blue and the red to 110 VAC and off she ran.

No relay necessary.

I thought someone else may find it useful.

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Unread postAuthor: Technician1002 » Wed Jul 29, 2009 1:54 pm

boyntonstu wrote:http://i348.photobucket.com/albums/q339/BoyntonStu/8000compressor.jpg

I connected the blue and the red to 110 VAC and off she ran.

No relay necessary.

I thought someone else may find it useful.

BoyntonStu


Grab a pic of the connections on the compressor itself. Most often the relay is disguised as a plug that attaches to the terminals of the compressor. If you didn't remove it, it if it exists, is still on the compressor.

http://www.e-refrigeration.com/index.php?page=repairing-a-compressor

The relay will plug directly onto the three pins shown in the link above.

Various start relays look like these, but are most often black in color.
http://www.tdspares.co.uk/products.asp?cat=81
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Unread postAuthor: POLAND_SPUD » Wed Jul 29, 2009 2:18 pm

@tech
Some compressor manufacturers state that a high percent of the compressors that are returned to them have no faults.

If you find that the compressor is not running or you hear the telltale "clicking sound" of the overload, then you need to check the start components as well as the compressor motor windings
I couldn't serve as a better example here... the compressor I use must have been produced about 30 years ago (or more)

it broke down in the early or mid 90ties and since then the fridge was kept outside...

a few months ago my previous compressor broke down so I decided that I might as well check that old piece of junk... and voila it works!!

@boyntonstu I am happy that you've managed to get it done... now consider getting a pressure reservoir (with proper pressure rating and pop-offs or at least a home made pressure release valve) for it...
trust me these things are ten times better with a tank

ohh one more thing - consider using adapters I described - they make life easier when you have to replace the compressor.. and stick to threaded fittings because modularity rulezz
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Unread postAuthor: boyntonstu » Wed Jul 29, 2009 5:02 pm

POLAND_SPUD wrote:@tech
Some compressor manufacturers state that a high percent of the compressors that are returned to them have no faults.

If you find that the compressor is not running or you hear the telltale "clicking sound" of the overload, then you need to check the start components as well as the compressor motor windings
I couldn't serve as a better example here... the compressor I use must have been produced about 30 years ago (or more)

it broke down in the early or mid 90ties and since then the fridge was kept outside...

a few months ago my previous compressor broke down so I decided that I might as well check that old piece of junk... and voila it works!!



@boyntonstu I am happy that you've managed to get it done... now consider getting a pressure reservoir (with proper pressure rating and pop-offs or at least a home made pressure release valve) for it...
trust me these things are ten times better with a tank

ohh one more thing - consider using adapters I described - they make life easier when you have to replace the compressor.. and stick to threaded fittings because modularity rulezz


Thanks,

I don't understand why filling a chamber directly from the A/C compressor is not as good as first pressurizing a reservoir and then filling a chamber from the reservoir. Isn't a chamber also a 'reservoir'?

The capacitor is definitely a run capacitor. Since it was connected with only 2 wires, it seems that the wiring is complete.

Next, a filter, and a quick disconnect.

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Unread postAuthor: POLAND_SPUD » Wed Jul 29, 2009 5:34 pm

well there is nothing wrong in not using a tank (well maybe apart from the fact that constant turning on and off will gradually damage any appliance )

trust me getting an air reservoir is well worth the fuss... sometimes I don't even need to turn the compressor on as the tank it's already pressurised...

besides I think you might need a chamber as a sort of buffer... it's already quite dangerous with a fridge compressor and an AC compressor has higher flow... you might not have enough time to turn the compressor off

if you could get a scuba trank or somethign you would only need to turn the compressor on and when you reach 600 psi or so you could turn it off... that shoudl last for a while
depending on the chamber volume of the gun of course... but if you are into high pressures then it's highly unlikely that you'll use large volume guns for practical reasons... (and even if you do then you'll really find that having a sort of buffer will save your time as the compressor could pump air when you aim and fire the gun)
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Unread postAuthor: boyntonstu » Wed Jul 29, 2009 7:05 pm

POLAND_SPUD wrote:well there is nothing wrong in not using a tank (well maybe apart from the fact that constant turning on and off will gradually damage any appliance )

trust me getting an air reservoir is well worth the fuss... sometimes I don't even need to turn the compressor on as the tank it's already pressurised...

besides I think you might need a chamber as a sort of buffer... it's already quite dangerous with a fridge compressor and an AC compressor has higher flow... you might not have enough time to turn the compressor off

if you could get a scuba trank or somethign you would only need to turn the compressor on and when you reach 600 psi or so you could turn it off... that shoudl last for a while
depending on the chamber volume of the gun of course... but if you are into high pressures then it's highly unlikely that you'll use large volume guns for practical reasons... (and even if you do then you'll really find that having a sort of buffer will save your time as the compressor could pump air when you aim and fire the gun)


O.K. I understand your point.

However there is an alternative.

I own a 2 cylinder wobble pump that goes to 150 psi, no tank.

I use it to fill my car tires.

There is a relief valve on the trigger mechanism.

I start the pump with no back pressure and the relief valve open.

I connect the Schrader and let go of the relief valve.

When I remove the connection to the Schrader, I press the relief valve again until I turn the pump off. No load, no struggling.

Less wear and tear, and nothing extra to worry about.

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Unread postAuthor: Technician1002 » Wed Jul 29, 2009 8:22 pm

boyntonstu wrote:
The capacitor is definitely a run capacitor. Since it was connected with only 2 wires, it seems that the wiring is complete.

BoyntonStu


What's so hard at looking at the side of the compressor under the little cover?

The difference in a run and start capacitor besides the size is the presence or absence of a relay ON THE SIDE of THE COMPRESSOR that disconnects the capacitor after the compressor starts.

It is true there are two leads that connect to POWER. Between the capacitor and motor is 3 leads.

On the leads shown here;
Image

BLUE is the RUN. It connects to both the RUN on the compressor through the coil on the relay if one is present and POWER on the capacitor.

RED is COMMON. It connect to the common terminal of the compressor.

Grab a pic of the connections on the compressor itself. Most often the relay is disguised as a plug that attaches to the terminals of the compressor. If you didn't remove it, it if it exists, is still on the compressor.


Yellow is EITHER START or RUN CAP. To tell, you have to take the cover off the compressor and look for a START RELAY.. What is so hard about looking under the cover? I suspect the yellow wire connects to a terminal on a relay under the cover. Until someone looks there is no way to tell what is under the cover.
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Unread postAuthor: boyntonstu » Thu Jul 30, 2009 7:09 am

What's so hard at looking at the side of the compressor under the little cover?

The window A/C was one block from the ocean and the bolt/nut are rusted.

You wouldn't believe all the corrosion inside the unit.

I will spray it with WD-40 and I will get it open.

Sorry for being lazy.

I tend to agree with your train of thought.

Looking at the photo:

Red - directly to motor.

Blue - to one side of cap and onto motor.

Yellow - from other side of cap to motor.

The yellow goes to the starter winding and remains connected, or a relay opens.

Are there any other options?


BoyntonStu

I thank you for your patience.

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Unread postAuthor: POLAND_SPUD » Thu Jul 30, 2009 8:41 am

well I wasn't referring to the back pressure only... I meant that turning them on/off all the time puts more wear on the parts and the motor

I am not saying that you have to get a tank... I am only suggesting that it makes life easier in the longer run...
I usually start the compressor under no load as I have two ball valves on the setup.. one between the tank and the compressor and one for venting the volume between the tank and the compressor..

so actually I can close off the tank, vent the air that on the air output, turn the compressor on and then open the tank (it's usually already at 250 psi as I see no point in venting it after each use) and I have lots of air at hand, which translates to -> no waiting
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