Automotive Air Conditioning Information Forum (Archives)
compressed air for finding large leaks
lovemybadkitty on 
Sat May 12, 2007 2:35 PM 
Can you use compressed air for finding large leaks? Also when vacuuming a system do you open both the high and low side manafolds on a gauge set?
TRB on 
Sat May 12, 2007 2:45 PM
I would suggest Nitrogen over compressed air do to the moisture content. Yes open both valves when pulling a vacuum.
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HECAT on Mon May 14, 2007 8:15 AM
In addition to the moisture, there must be a reason behind the fact that the following safety warning is required on all R&R equipment.
Caution â Do not pressure test or leak test HFC-134a service equipment and or vehicle air conditioning systems with compressed air. Some mixtures of air and HFC-134a have been shown to be combustible at elevated pressures. These mixtures, if ignited, may cause injury or property damage. Additional health and safety information can be obtained from refrigerant manufacturers.
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Test Specimen on Mon May 14, 2007 11:15 AM
Compressed air mixed with non-CFC refrigerants and solvents can create flammable mixtures. The elevated partial pressure of oxygen increases the ability of all materials that can combust to become more flammable. It is the same as lighting a cigarette in an oxygen tent - what used to burn slow now can go boom.
Using nitrogen to leak check is much safer. AFAIK, no one has gotten themselves blown up using R-134a and air, but there have been fatalities from people mixing air and R-22 together at elevated pressures. The one that got the most attention was someone welding a tank containing R-22 and air - parts of the tank went over a mile, and there was no trace of the welders.
Both R-134a and R-22 don't burn at atmospheric presure in air, so are considered non-flammable. Materials that burn at atmospheric pressure in air are marked as flammable.
TRB on Mon May 14, 2007 11:26 AM
This gives me a little chuckle this morning. While I completely agree with the follow up posts!!!! When has anyone been concerned about a refrigerant blowing up these days? I say that tongue and cheek as we have so many flammable refrigerants being pass off as R12 replacements. A little compressed air and R134a seems like it would be way down the lists of combustible refrigerants.
Nitrogen is the proper method along with adding a little R134a for smaller leaks.
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mk378 on Mon May 14, 2007 2:14 PM
Anyone who would consider welding on a tank while it contains any gas under pressure deserves to get blown to smithereens.
lovemybadkitty on Mon May 14, 2007 5:52 PM
I guess it as matter of finding a small can of nitrogen. I am trying to cut costs and don't really need a large amount. Do they sell nitrogen in small cans? When the gauge set was installed when I opened both high and low sides I got almost 0 vacuum and when turned off dropped immediately.
Dougflas on Mon May 14, 2007 6:58 PM
WHEN USING NITROGEN YOU MUST USE A REGULATOR ON THE TANK!!!!!!!!!Smallest tank I ever saw was 40 cuft.
mk378 on Mon May 14, 2007 7:12 PM
The regulator is the expensive part. Maximum test pressure 150 psi or you risk bursting the evaporator or other parts of the low side.
The gas is not expensive even in a large bottle, but they charge monthly rent on the bottle. You're probably money ahead to return a nearly full bottle than to keep it around waiting for the next possible job.
Test Specimen on Mon May 14, 2007 8:14 PM
Another fatal boom just happened recently (several months ago) when a tech servicing an ice machine in a Philadelphia area Friendly's restaurant used unregulated nitrogen to pressurize the system. No one is sure what the pressure the system was at when the compressor shell ruptured while his head was next to it.
Please use the right equipment and materials when you pressure leak check systems.
TRB on Mon May 14, 2007 8:18 PM
Very important suggestion! I tend now and then to over look these types of items (regulator) as they just a given requirement. Thanks for the follow up posts!
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Edited: Mon May 14, 2007 at 8:19 PM by TRB
Karl Hofmann on Mon May 14, 2007 8:43 PM
I have seen small 1Kg Nitrogen pressure test kits at my wholesaler. They are designed for engineers working on smaller systems who will be working in tight areas or where you cant take a large bottle
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penright on Tue April 01, 2014 8:59 AM
What about using CO2 from a mig welder?
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