Trouble finding A/C leaks? (especially with 134a)
by John Noble, www.coolflow.com
Appeared in
May/August 2001 Cool
Profit$ Magazine
Even with all the gadgets like electronic leak detectors and fluorescent dyes, why are today’s technicians still having a terrible problem detecting refrigerant leaks?
To help the readers of Cool Profit$ do a better job of detecting leaks, below are some of the “trade secrets” acquired over the last twenty-eight years. Like many of you, I’m a seasoned, veteran a/c technician who learned to cope with problems in some innovative, unconventional ways.
Note: You won’t find these procedures listed in the recently published MACS Service Reports (June 2001 edition)
“Special update on refrigerant leak detection.” (I offered them, but they were rejected). However, visit us at Cool Flow, Inc., Houston, Texas and I’ll show you how we are able to consistently locate leaks within 5-10 minutes, from start to finish, without the use of fluorescent dyes.
So here is my MACS-spurned Basic Leak Detection Course 101: Principles and Practices of A/C System Leak Testing with Nitrogen. I’m glad that my solutions will finally be heard.
Understanding the Basics System Residues hide leaks. Sludge and residues coat the interior of system components and temporarily seal corrosion pits, fissures, seams, seals, o’rings, and other small leak points. Some of those residues include refrigeration oils, acids, desiccant, pulverized metal, Teflon piston ring material, brazing fluxes, dye particles, etc.
Overcoming Residue Surface Tension: Leaks are harder to find because leak testing is performed with the system turned off. Lost are the benefits of an operating system: a) constant washing of interior surfaces of components; b) higher operating pressures that encourage leaks. With a system at rest, the undisturbed residues mentioned above are able to coat the insides of the evaporator, condenser, compressor, and other components. When Residue Surface Tension is greater than the interior pressures’ ability to displace it, there is no leak occurrence, thus no leak detection.
Residue Displacement: If surface tension is the culprit, then how do we overcome it? Answer: By adding 4-ounces of chlorine-based refrigerant R-22 to the system. R-22 disturbs the surface tension. We follow that by pressurizing the system with 175-200 psi of nitrogen.
Both are cheap.
At the higher system pressure, the R-22 overcomes the residue surface tension and forces the leak path to reopen. Now, enough R-22 gas is available so that leaks are detected easily. The R-22 is the residue-displacing agent.
R-22 summary. R-22: (a) creates a leak path because of its oil solubility and residue displacement potential; (b) is more readily detectible by electronic leak detectors than HFCs; (c) is non visual-dependent, unlike dyes, thus can be used effectively to locate leaks in enclosed areas; (d) will not cross-contaminate nor cause any harmful consequences to CFC, HFC, nor blend refrigerant systems (i.e., after leak testing an HFC (R-134a) system using R-22, there is typically zero percent cross-contamination if evacuated afterwards).
Nitrogen summary. Nitrogen has the following qualities: (a) inert, very dry and non-flammable; (b) does not go into solution with refrigeration oil to create non condensable pressure problems (i.e., after leak testing an HFC (R-134a) system using R-22 and nitrogen, there is typically zero percent non condensables (nitrogen or air), if evacuated afterwards).
Diluted Liquid Soap. Speed is important to technicians when performing a leak test. Large and medium size leaks can be quickly located in exposed areas such as under hood components by applying diluted liquid dishwashing soap directly to suspected leak points.
Multiple Leaks. If a large leak is discovered repair it and perform a follow-up leak test. Leak tests should be performed following each repair until all leak points are found and fixed.
Pinpoint versus Area Testing Pinpoint Accuracy. Technicians need to know exactly where leaks exist. Consequently, leak testing needs to be pinpoint accurate, regardless whether by visual or non-visual means. With dyes, the detection is strictly visual and general area, not pinpoint. Dyes do not provide the rapid and finite definition of the Combination Method [non-visual: electronic leak detector detecting the nitrogen-pressured R-22, and, visual: diluted soap solution bubbling].
Electronic Leak Detectors. Heated diode leak detectors are currently the best non-visual, dependent leak detection instrument for sensing a gaseous leak. They have the necessary characteristics of sensitivity, repeatability and recoverability (after a leak), which are so important.
Releasing Test Mix. The EPA approved the releasing of the “test mix” (R-22 & nitrogen) with the stipulation that: “All existing refrigerant within the system be recovered properly, and a 102mm (about 4”) mercury vacuum drawn on the system.”
By their definition, the R22-nitrogen test mix used for leak testing is not considered a refrigerant and therefore may be released to atmosphere. Their rationale is that one tiny loss which results in the discovery and repair of a leak reduces the greater loss over the life of a system. It’s better than multiple recharges of refrigerant and multiple losses to atmosphere.
Note: We’ve learned that the R22-nitrogen test mix should be released outside the building via copper (or other) tubing to prevent fouling the air inside the shop. This prevents false alarms by the leak detector. Also, always maintain a well-ventilated work area.
Summary
There is currently no equally effective (in all situations) substitute for the combination leak test method described above. It has neither the problems nor shortcomings of dye. I have heard the argument that nitrogen is dangerous. Well, the stationary industry has been using it for at least 60 years, and my company has been using it since 1973. Some of the major stationary manufacturers think that is important enough to dedicate a section of their training manuals exclusively to its use for leak testing their a/c systems. It is not unsafe, unless one uses it improperly. Mobile a/c technicians are simply untrained in its use. What a shame, it is so simple and effective and easier, safer, and cheaper, etc.
Once upon a time, folks were afraid to fly in an airplane that didn’t have a propeller—it was thought to be too dangerous. I encourage any a/c technician to get a good quality nitrogen regulator and bottle of nitrogen from a welding supply store. Set the regulator to 200
psi. It is safe to use with all conventional a/c systems, and will not damage any system components.
Make sure that the nitrogen bottle is secured to a wall or in a dolly, and that everyone in the service department is taught not to fool with the regulator setting. Or, install an Allen head set screw and lock nut with the regulator so that it can’t be adjusted once it is pre-set. We have safely tested a/c system components at 200-psi nitrogen pressures on over 40,000 tests. Remember, 200 psi is only about 50 psi higher than the compressed air lines used by you and every other technician nation wide. I encourage all technicians who aspire to become more professional in a/c service to invest in a good quality nitrogen regulator and bottle. Then take the time to practice the method. You will be doing a service to yourself and your
customers.
$$$
Before opening an automobile repair business, Cool Flow, Inc. founder John Noble spent 7 years in the aircraft service industry, and prior to 1971 worked as an FAA certified airframe & power plant technician. During the next 4 years he began to make the transition to specializing in automobile a/c related services. Today, the company is currently undergoing another transition into development of several a/c related products, which may be seen on its website:
www.coolflow.com.
Editor: Soon you will be
able to check in with “current” radiator and a/c industry vendors on the web at:
www.imcool.com/buyersguide/.
Vendors: If you would like to be listed as a vendor to the automotive (and Heavy Duty) radiator and A/C service industry, please call, fax, email or fill out the form on the imcool.com web site. Look for Buyer’s Guide Data Entry Form.
Your cost to be listed on the web site and in the 2002 Annual Guide is only $12. For that, you also get a subscription to Cool Profit$ Magazine. In addition, your web listing will be maintained for free (name, contact, address, phone, email, URL, etc.). One heck of a deal.
i'm doing some research for my company and am wondering how well the leak detecting fluids work and if there is any kind of harm done to the system. Our systems area larger than most automotive systems but i'm just trying to get a feel if my company should use these fluids or not. any response will be appreciated
Reply to david
John Noble – Houston, TX
March 27, 2008 - 19:49
Subject: R134a Leak Detector Fluids
David,
Are you referring to fluorescent dye? My preference is to avoid the use of dyes, per the article. Yes, some dyes have been known to cause problems, but the main reason for my use of the combination leak testing method is that it has always been far more effective, quicker, easier, and less costly than the use of dyes. It is effective for use on systems of any size. Trane, Copeland and other manufacturers once taught the method in their factory manuals. One of the greatest tragedies in the a/c service industry has been the censorship by trade associations against educating techs in the method. As a result, a whole generation of techs does not have a clue about the basic concept of “residue displacement” and how relevant it is to finding leaks. Thus, consumers have suffered untold billions of dollars in misdiagnosed leaks, and unnecessary repairs. I hope that your company will implement the combo-method as its standard operating procedure. It works! Best Regards!
Dennis McCarty
November 04, 2007 - 08:37
Subject:
John,
#1. How do you charge the R22 into the system?
#2. How do you recover/release the R22/Nitrogen after the testing is done? (to make sure there isn't any contamination into the 134A source eventually).
#3. Am I correct in understanding that mobile air conditioning system can tolerate 175-200 PSI on the low pressure side of the system during testing?
#4. What flush system and fluid would you recommend for a small shop that wants to do a good job but can't quite afford the Hecat H-1000?
Thanks!!!
Dennis McCarty
Dennis McCarty
October 26, 2007 - 21:42
Subject: nitro/R22 testing
John,
Where do you get R22 and what do you use to get it into the system?
I just bought a nitrogen regulator that goes up to 100psi. Will that be enough pressure to find most leaks?
Thanks in advance for your input to this problem that I have long wondered about. Your article is most appreciated
Reply to Dennis McCarty
John Noble – Houston, TX
October 26, 2007 - 22:10
Subject: Where to buy R22, and is 100 psi nitrogen pressure enough?
Dennis,
Normally, refrigeration supply houses carry R22, as it is used primarily for residential and commercial a/c & refrigeration systems. It can also be purchased through independent refrigerant suppliers. You can also use R12, although it is more expensive. A license is needed to purchase either one.
As to whether 100 psi is sufficient, the answer is maybe, depending on how big the leak. I have found that the most difficult leaks require 200 psi to locate. But, since you are only able to develop 100 psi, you might try waiting longer for the test gas to concentrate in the evaporator before testing it with your electronic leak detector. Even at 200 psi, I sometimes have to give it 10 minutes or so before inserting the probe in the center a/c outlet, and turning the blower on "Low" momentarily while listening for an "up-tick". You may or may not find it at 100 psi, but you can try.
JIM FREDIANI – orange park fl
August 15, 2007 - 18:54
Subject: leak test wtth nitrogen
to insure the safe use of nitrogen to presure system a pressure relief valve down stream of the regulator set slightly higher than the test pressure ( say 250 psig for your appltcation) would protect against a possible biuld-up of pressure due to a leaking regiulator.
Reply to JIM FREDIANI
John Noble – Houston, TX
August 15, 2007 - 20:21
Subject: Pressure relief valve
Jim,
It’s a good thought, but 250 psi might burst some of today’s evaporators since most core manufactures have quit using the welded aluminum strap across each aluminum tank. The strap prevented "accordian" effect ruptures during testing. Although I’ve never experienced a pressure increase due to regulator failure, if I decided to install a relief valve, I’d use a 200 psi type, and adjust the regulator slightly below that point. It is really best to stay at or below 200 psi because your leak find rate will be very effective as long as you’re testing within the 175-200 psi range.
John
John Noble – Houston, TX
August 03, 2007 - 12:14
Subject: The use of R22 as a key ingredient ("residue displacement agent") in Leak Testing.
David,
Add R22 as a LIQUID, not as a gas. It is quicker. Add R22 by WEIGHTnot pressure. If you don't have a scale to weigh the amount, you can estimate the amount by using the rule of thumb 1 ounce per second. After drawing a deep vacuum, let the refrigerant flow into the Hi side AND Lo side simultaneously for four seconds, which should be approx 4 -6 ounces. Pressurize with nitrogen to 200 psi, and begin looking for leaks, first with your heated diode type leak detector. Apply diluted liquid Palmolive dishwashing liquid soap (mixed with water to a pale green color) to pinpoint leaks on visible components. Some leaks are so tiny that they don't bubble, yet the leak detector will pick it up anyway, so given the choice between believing the leak detector or what you don't see (bubbling)__believe your leak detector! Keep practicing. You'll soon get the hang of it, and it WILL all start to make sense. Your leak test find-rate will greatly improve as you begin to become more proficient.
David Lasly – Las Vegas, Nevada
August 03, 2007 - 07:01
Subject:
I understand that it is OK to add R22 up to 20psi on a typical non-operating system and then add nitrogen up to 120psi for a trace-gas leak test. Is 20psi a safe amount of R22 to use for this purpose?
John Noble
– Houston, TX