Freon question

[Profish00]

The service man came out today and put some stop leak in my system. When he was adding some freon back in the system he had me hold the bottle upside down. Why do they hold it upside down sometimes or do you allways hold it this way? My real question is what is the difference in the bottle being upright as compared to upside down? Also on the name plate it states low side 144 high side 278. I noticed on his guages it read that the high was around 275 but the low side read around 70. It was also around 93* outside. I also noticed the blue guage only goes to 120. Thanks Mark

[LazyPup]

I appologize for my delay in responding but this is a very short post which raises a number of rather complex and potentially controversial questions which required a bit of thought on how to address it.

While I am sure there are two sides to every story, based solely upon the information presented here my first reaction would be to say this would be the last time that service tech worked on my system.

In the residential and commercial HVAC industry the accepted method of dealing with leaks in a system is to use an Electronic Halogen Leak Detector to locate the leak then take the necessary steps to make a permanent repair.

Some refrigerants cause rapid deterioration of neoprene O-rings used in fittings and there are a number of "Stop Leak" products designed to address that particular problem, however, while neoprene O-rings are common in automotive AC systems in residential systems nearly all joints are brazed copper or flare fittings which do not have neoprene O-rings thus the use of the stop leak products is marginal at best and in many cases it will void the warranty on your compressor and can cause problems with compressors and expansion valves.

While there is no mention of it in the post,I feel it fair to mention here that there is also a Leak Detector Dye that can be put in the refrigerant. These products should also be strongly avoided.

Now for the Refrigerant charging technique. When a refrigerant cylander is upright there is a pocket of gasseous refrigerant at the top of the cylander. As the refrigerant gas is drawn off the ambient air heat surrounding the cylander boils some of the liquid to a gas to maintain equal pressure in the cylander. The gasseous refrigerant is drawn into the low side or suction line of the AC unit by the compressor.

If the refrigerant cylander is turned upside down the pocket of pressurized refrigerant gas is above the liquid and it pushes liquid refrigerant down into the charging manifold. Under idea conditions that liquid refrigerant will boil to a gas in the charging manifold lines and enter the AC as a gas and this technique is used by some technicians to speed up the charging process but there is a very high risk that some of the liquid refrigerant will carry into the AC unit and get sucked into the compressor cylander. Liquid is not compressible so when this occurs we hear a very loud knocking noise which is known in the trade as "Slugging". This is a very risky procedure because slugging can cause permanent damage to the compressor valves and this method should be avoided.

Having said that, there is a device manufactured by Imperial Eastman Corp called a "Kwik Charge" that can be attached to a refrigerant cylander, then the charging manifold is attached to the kwik charge. With this device we can keep the refrigerant cylander upside down thereby forcing the liquid into the Kwik charge where it is converted to a gas before entering the charging manifold. (See the attached illustration.)

Under no circumstances should a technician ask a customer or untrained individual to hold a refrigerant tank while charging, especially if the tank is upside down. While it is extremely rare, none the less, the risk is present that the charging manifold could come loose and permit some of the liquid refrigerant to spray out. At standard atmospheric pressure the boiling temperature of R-22 is approximately -41 degF. Ask any experienced HVAC tech and they will confirm that even a drop of liquid on your skin will result in instant frostbite and if it should happen to splash in your eye it could freeze the eyeball and cause blindness. Refrigerant tanks should not be handled by anyone who has not been properly trained, especially when the valve on the tank is open.

The pressure you found printed on the data plate are factory test pressures and do not reflect the correct operating pressure. The good news is the pressures you noted on the guages is the correct pressure for an AC operating on a 93degF day.

Now for your question about the pressure range on the charging manifold guages.

A PSIA guage would indictate PSI-absolute which indicates all pressure above absolute zero thus a PSIA guage would show standard atmospheric air pressure at approximately 14psi.

The RED guage on a charging manifold is calibrated as a PSIG guage. On the PSIG scale the meter is calibrated to show zero at standard atmospheric pressure and the pressure indicated is PSI above standard atmosphere. The guage is the calibrated from zero to 350 or 400psi which is the highest operating pressure we are likely to encounter on an AC when the compressor is running.

The BLUE guage commonly called the Low Side guage is calibrated as a "Compound guage." On a compound gage pressures above standard atmospheric pressure are calibrated as PSI readings and printed in black on the guage, while pressure below atmospheric pressure, commonly called vacuum pressure are calibrated in "Inches of Mercury" (in/Hg) and printed in red on the guage. For AC refrigerants the low side pressure will normally be 70psi or less so there is no need for the guage to go higher. For refrigeration the normal low side pressures will typically be under 10psi and many refrigerators operate with a vacuum on the low side.

We also use the vacuum guage when pulling vaccuum on the system to insure it is properly dehydrated prior to charging the refrigerant or to test for leaks.

[Profish00]

Thats the best explanation on (how it should be done) Thanks for the answer.

[dnpeters]

LazyPup - This is probably apples and oranges, but filling A/C systems is something lots of us find confusing. Some of the automotive R-12 to R-134 conversion kits indicate the cans of R-134 should be inverted. Is this because they're going into an empty system, or are these cans designed to reduce the risks you mentioned? Thanks.

[mud]

r-134a is a blend (combination of different refrigerants) and needs to be put in as a liquid. Charging as a gas can cause it to fractionalize because the different gasses can leave the tank at different rates. If that happens the blend has been altered and will not perform as intended.
Whenever charging any refrigerant as a liquid care must be taken to assure its not entering the compressor as a liquid.

[dnpeters]

Thanks, that helps. Also, I suspect the tiny nozzles on those small cans wouldn't be capable of putting out sufficient volume of liquid for it to reach the compressor before turning to gas.

[LazyPup]

A 30# refrigerant cylander has a 1/4" diameter discharge valve whereas the small can adapters have a 1/8" peircing valve thus even if the small can peircing valve is fully open its capacity is only 1/4 that of the 30# cylander. If you were then charging from the small cans through a regular charging manifold there should be sufficient length of the refrigerant lines to permit complete liquid to gas conversion before entering the system however, if you are charging through one of those little DIY can adapters with the short 12" or 18" line there is still a great risk of flooding liquid to the compressor.

For my personal charging manifold I prefer a Robinaire charging manifold with a 4 line adapter and I use the optional 5' lines with check valves. With 5' lines I have a 10' length of line between the cylander and the unit at all times.

With the 4 line adapter I can connect one line to the vacuum pump or recovery unit and one line to the refrigerant cylander, then connect the High & low side lines to the condensing unit. In this manner I can change from vacuum or recovery to charging without disconnecting any lines, therefore I have almost zero possibility of air or moisture getting into the system when making the change over.

[Piper]

.....Why do they hold it upside down sometimes or do you allways hold it this way? My real question is what is the difference in the bottle being upright as compared to upside down?

When the can is upright vapor is coming out of the top. When the can is upside down liquid is coming out. This is risky practice because you can damage the compressor by flooding it with liquid which does not compress.

confused: Also on the name plate it states low side 144 high side 278. I noticed on his guages it read that the high was around 275 but the low side read around 70. It was also around 93* outside. I also noticed the blue guage only goes to 120. Thanks Mark

I would have to know what type of refrigerant your unit has in it to comment on the pressures. Older refrigerants ran at lower pressures than the new ones. It's time for yur serviceman to get a new set of gauges. Hope this helps.

[Profish00]

[QUOTE=
I would have to know what type of refrigerant your unit has in it to comment on the pressures. Older refrigerants ran at lower pressures than the new ones. It's time for yur serviceman to get a new set of gauges. Hope this helps.[/QUOTE]
R-22 and from my understanding those pressures are good 70/275

but please correct me if Im wrong