Automotive Air Conditioning Information Forum (Archives)

Provided by www.ACkits.com

We've updated our forums!
Click here to visit the new forum

Archive Home

Search Auto AC Forum Archives

Charging with 30lb tank

70monte on Sun July 01, 2012 6:56 PM User is offline

Country of Origin: United States

What is the preferred way to charge from a 30lb tank, tank upside down or right side up? I keep reading differing opinions and wondered which way is the best. Are there any benefits or negatives for each method. Thanks.

Wayne

buickwagon on Sun July 01, 2012 10:30 PM User is offline

Valve up is the most stable orientation. If it has two valves, one has a red handle and a dip tube to haul liquid refrigerant off the bottom, the other has a blue handle and no dip tube so it delivers vapour. If it has one valve, then there is no dip tube and it delivers vapour with the valve up.

Charging with liquid into a vacuum is the fastest way to get the initial charge in. Then switch to vapour before starting the engine and topping off the charge through the low pressure port only. Charging with vapour is slower but much safer as there is no risk of liquid slugging a running compressor.

(nb: the above assumes you are using a single refrigerant like R12 or R134a. Blended refrigerants must be charged as a liquid only. Otherwise the differing vapor pressures will cause the constituents to separate and you won't get the correct proportions.)

-------------------------
I've saved hundreds on service by spending thousands on tools.

Edited: Sun July 01, 2012 at 10:31 PM by buickwagon

Cussboy on Mon July 02, 2012 12:40 AM User is offline

Quote
Originally posted by: buickwagon
Charging with liquid into a vacuum is the fastest way to get the initial charge in. Then switch to vapour before starting the engine and topping off the charge through the low pressure port only. Charging with vapour is slower but much safer as there is no risk of liquid slugging a running compressor.

What he said.

NickD on Mon July 02, 2012 7:30 AM User is offline

Static charge is most important without getting air into the system for an initial charge.

Can connect the red to the high side, yellow to the tank, and blue to your vacuum pump. Tank valve is closed, open the low and high side ports on your manifold gauges and draw a deep vacuum. Then close the high and low side ports, disconnect the vacuum pump, crack open the tank valve to purged out that line and quickly connect it to the low side port. As the AC system has high positive pressure, some refrigerant will leak out rather than having air leak in, then charge as normal.

Don't have to do this with a charging station, does this for you. To get in the maximum static pressure, AC system should be as cool as possible, and tank as warm as possible. Not concerned with charging by liquid, more concerned about doing it right without air in the system.

Could drive you car to a production line, where they just connect the low and high side, automatically draw a deep vacuum, pump in the correct amount of oil and refrigerant in a matter of seconds. Also doing it the right way without switching hoses losing your deep vacuum.

buickwagon on Mon July 02, 2012 9:24 AM User is offline

Ok, I'm a bit confused by that procedure.

What I have been doing is connect the red and the blue to the high and low pressure ports, respectively, and the yellow to the vacuum pump. Open the service port valves on the red and blue hoses, start the pump and open both the red and blue manifold valves. Once the deep vacuum is pulled, I close the manifold valves and move the yellow hose to the tank. I open the tank vapour valve and purge the line by depressing the Schrader valve stem on the second yellow port of the manifold. Once purged, I closes the vapour valve and open the liquid valve, record the tank weight and open both manifold valves. Once the vacuum has drawn in all the liquid it can take, I close the red manifold valve, close the liquid valve and open the vapour valve before starting the engine and topping off the system to the total required weight.

I cannot lose the vacuum, the system is separated from atmosphere by valves at all times so no air can ever enter the system, and any escape of refrigerant through purging is absolutely minimal. No speed required. Is there a reason I am missing that your method of moving the blue hose around is preferred?

-------------------------
I've saved hundreds on service by spending thousands on tools.

mk378 on Mon July 02, 2012 1:19 PM User is offline

If you have a second yellow port on the manifold, you should buy a second yellow hose and connect it to the vacuum pump (through the port with no shrader valve for minimum restriction). Then you can evacuate and switch over to charging without breaking any connections or needing to purge.

Edited: Mon July 02, 2012 at 1:20 PM by mk378

Bob on Mon July 02, 2012 3:34 PM User is offlineView users profile

Do they make a connector that converts the center hose port to a port with two connections on it?

buickwagon on Mon July 02, 2012 3:52 PM User is offline

If I remove the Schrader valve core, then I need to add a manual valve.

-------------------------
I've saved hundreds on service by spending thousands on tools.

mk378 on Mon July 02, 2012 5:07 PM User is offline

You use the valves on the cylinder and the pump. Evacuate: close cylinder, open pump. Charge: close pump, open cylinder.

You can leave the shrader in the port on the back; that goes to the cylinder. The port on the center bottom of the manifold should have no shrader in the first place.

Bob, with R-12 it was easy to buy tees (standard flare tees). Acme thread tees may also exist. Some people have drilled out the blank hose holder port on the back center of a cheap manifold to make it into a 4 hose type. This conversion is of course not reversible.

buickwagon on Mon July 02, 2012 9:25 PM User is offline

Ah. My pump doesn't have a valve, but if it did, that would work. And you are correct, the centre bottom on the manifold has no Schrader valve. The more I think about it, the more I like the idea of adding a manual valve. The line to the tank could be purged with the pump. No loss of refrigerant by purging, no question about getting air into the system.

1/2" Acme fittings are kind of hard to come by (at least around here) but if you have a lathe, it's easy to make a 1/4" female flare x 1/2" male Acme or maybe a 1/4" mip x 1/2" male Acme adapter out of brass. I've made several of the former now.

-------------------------
I've saved hundreds on service by spending thousands on tools.

Edited: Mon July 02, 2012 at 9:27 PM by buickwagon

Leggie on Mon July 02, 2012 10:13 PM User is offline

The manifold gauges you get at Harbor Freight has a Y port for the center. one is straight-thru and other has a schrader.

Hook up low/high to vehicle.
Center-straight to refrigerant tank.

Evacuate through schrader port on center. This will evacuate the inside of manifold as well as the hose going to the refrigerant and you can detach the vacuum pump hose and schrader will isolate it.


If you're using a standard manifold, just evacuate the system, turn off valves. Let just enough refrigerant flow out before attaching to the manifold to clear air.
The amount of air stuck inside the manifold itself is minimal.

Since speed is no issue, just charge as vapor into both high and low until it won't go in anymore. This will activate the pressure switch.

Close the high side and start charging into low side as vapor.

This will result in a more accurate charging as you can monitor the charging progress on the scale better.

Don't trap any liquid refrigerant in the hose. It will escape when you disconnect the hose and it will result in a major charge error.


70monte on Mon July 02, 2012 10:14 PM User is offline

Thank you for the information. I have always charged using the vapor method and didn't know if I would gain much by trying the liquid method. I'm not usually pressed for time so I doubt going the liquid method route would gain me much versus possible compressor damage if I did something wrong. Thanks again.

Wayne

Leggie on Mon July 02, 2012 10:19 PM User is offline

If you're doing DIY recovery, its best not to do liquid. Any crap and sediments that collect in the recovery cylinder will get back into the system with liquid.
If you charge as vapor, all that stays behind in the tank.

johnbkobb on Thu July 05, 2012 12:27 PM User is offline

The following is a Four Seasons "Tech Tip" from www.4s.com

Hope this helps someone. I use the 30# can with scale method

"Charging with Cans, Guess Again?

Unlike the old days when an R12 system could be ½ pound on either side of full and still produce cold air, an R134a system is not as forgiving. The acceptable operating window for R134a cooling is about +/- 2oz of full. This is why technicians should recover and recharge to O.E. specifications rather than attempt to “top-off” a system that is being serviced for a low charge.The charging method you choose will make a difference in the accuracy of the final charge amount. For greater accuracy a charging station or a 30lb cylinder and an electronic scale is the preferred method of charging. The charging accuracy is questionable with the use of 12oz cans.One problem with can charging is a misunderstanding as to what is meant by 1 pound of refrigerant. Many technicians today still speak of 1 pound cans, which have not been produced since the late 1960’s. The industry also saw the use of 14 ounce refrigerant cans until the mid-1980’s. Today when we speak of 1 pound of refrigerant that amount is equal to 16 ounces. When we speak of 1 can of refrigerant that is an amount that is equal 12 ounces.
When recharging with a charging station or with a 30lb cylinder and an electronic scale,you need to add 2oz to the system capacity specification. This extra amount is necessary to compensate for the amount of refrigerant retained by the equipment or manifold gauge service hoses, whether you are vapor or liquid charging. So, if the vehicle calls for 28oz you will need to program in 30oz to ensure a full charge into the vehicle’s A/C system.NOTE: Some charging equipment requires you to add 2oz to the total charge amount,while others designs add the amount automatically. You will need to be familiar with how your equipment works. If in doubt read the equipment documentation or contact the manufacturer.
If the method of charging R134a is with 12oz cans, then you have to compensate for the amount of refrigerant to an even greater extent. You will still need to allow 2oz for the service hoses and since you can never completely empty a can of refrigerant you will need to allow for an additional 1oz per can. This occurs because the can’s pressure and the vehicle’s A/C system low side pressure equalizes, this stops the transfer of refrigerant. So, if the vehicle specifies 30oz, you would require the use of three cans.This would be 36ozs, less 2ozs for the hoses and 1oz per can times 3. That would put you within the operating window at 31oz. True, the final charge is 1oz over the required specification, but it is as close as you can “guess” with the use of small cans.
The drawback to using 12oz cans is when the specification calls for an amount requiring less than a whole can. Example – a system capacity of 24oz. You may believe 2 cans would give you a full charge, but actually only places about 20oz into the system. A 3rd can is then required to finish charging the system but you can only “guess” at the 4oz needed. You could easily over charge the system. You will also have an undetermined amount left in the can, leaving you to “guess again” at the charge on the next vehicle being serviced.
The amount of refrigerant retained in a 12oz can is dependent on the temperature of the refrigerant in the can. Whereas the amount of refrigerant retained in the service hoses is dependent on the length of the hoses and temperature of the refrigerant. The above examples are consistent with the refrigerant at room temperature around 85°F. When the component temperature is below 70°F, the amount retained could be twice as much.Heating the refrigerant with warm water (maximum 115°F) will increase the pressure of the refrigerant in the can and reduce the amount retained in the can to about ½oz."

70monte on Sun July 08, 2012 8:21 PM User is offline

johnbkobb,
Good info. I will have to remember this for future reference since I didn't add the additional 2oz when I last used my 30lb tank and scale.

Wayne

buickwagon on Mon July 09, 2012 7:24 AM User is offline

Quote
Originally posted by: johnbkobbWhen recharging with a charging station or with a 30lb cylinder and an electronic scale,you need to add 2oz to the system capacity specification. This extra amount is necessary to compensate for the amount of refrigerant retained by the equipment or manifold gauge service hoses, whether you are vapor or liquid charging. So, if the vehicle calls for 28oz you will need to program in 30oz to ensure a full charge into the vehicle’s A/C system.

That is an excellent article, especially about the waste inherent with cans and how to allow for it.

I don't have a recycle/recharge machine, just a recovery machine, and I fill from a 30# cylinder. So I have been charging direct from the cylinder. After pulling the vacuum, I close the hose valves and open the cylinder valve to fill the hoses with vapour. Then I take the starting weight of the tank before opening the hose valves to start the fill. I believe that this procedure inherently compensates for the amount in the lines and manifold. Am I missing anything?



-------------------------
I've saved hundreds on service by spending thousands on tools.

Back to Automotive Air Conditioning Forum

We've updated our forums!
Click here to visit the new forum

Archive Home

Copyright © 2016 Arizona Mobile Air Inc.