A/C system pressure test with Argon/CO2 instead of Nitrogen? - PeachParts Mercedes-Benz Forum

pwogaman · #1 06-20-2007, 11:16 AM

I am servicing my 85 300SD A/C system (with virgin R-12). Besides doing a vacuum pull to remove moisture and check for leaks (with a Welch 1397 pulling a whopping 17.7 cfm

), I want to do a pressure test to test for leaks. I've seen that many people do it with Nitrogen and a little R-22, but I don't have a Nitrogen tank laying around and don't want to buy or rent one if it is not necessary.

I happen to have a full 40 cf tank of Argon/CO2 for my MIG welder and a load of spare gas fittings that I could work onto the manifold. I also happen to have three fully functional military surplus explosion proof noble gas detectors (Argon, Neon, Helium). You can get your own here:

http://cgi.ebay.com/Phase-1-Instruments-Leak-Detector_W0QQitemZ130015628605QQihZ003QQcategoryZ53298QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

These detectors were designed to test fuel tanks and lines on airplanes without having to completely remove the fuel residue - simply presurize with a noble gas and sniff for leaks. I figure since they test for Argon, I could presurize my A/C system without having to add the R-22 and using my refrigerant sniffer.

Can anybody think of any downsides to this?

Also, how much pressure should be sufficient to pressure test a system? How much pressure do people use when checking with Nitrogen?

Many thanks

vstech · #2 06-20-2007, 11:27 AM

perfect fit. you should have no problems if you keep the pressure under 120psi. that is a great vacuum pump! we used them all the time on our service trucks, they are bullet proof! and FAST! kinda overkill on a car system, but hey! why not? I do not know how co2 would react with the oil in the lines, but I don't believe there will be any problems... I always use N2, but I got it... argon/CO2 should be fine. and having the tester is a huge plus!

pwogaman · #3 06-20-2007, 11:40 AM

Thanks for the quick response! BTW, I got the vacuum pump for $88 and the three leak detectors for $77 from DOD surplus auctions. The Leak detectors cost the U.S. Government over $14K each when new.

WD8CDH · #4 06-20-2007, 12:52 PM

The gas with the smallest molecular size will give you the best results. Got any helium lying around?

vstech · #5 06-20-2007, 12:57 PM

what? helium in the system??? help me... i'm leaking...

pwogaman · #6 06-20-2007, 01:06 PM

Quote:

Originally Posted by WD8CDH

The gas with the smallest molecular size will give you the best results. Got any helium lying around?

Actually I do, but I am reluctant to use it. What I have is a disposable balloon can from toys-r-us that is the about same size as your standard bbq propane can. I am afraid to use it because of the likelihood of a high percentage of air - and who knows what else - mixed with it. If I had a straight helium tank I'd consider using it.

BTW - if you're bored try this sometime: get a leaf collection bag (big one, about 55 gallon capacity) and fill it with helium, tie it off, and then let it go.

vstech · #7 06-20-2007, 01:15 PM

or better yet, fill it only about 1/3 full, it will go MUCH higher.

pwogaman · #8 07-02-2007, 09:17 PM

I think I found the answer to my initial question:

http://www.springerlink.com/content/d2p83044444065n8/

85chedeng300D · #9 07-02-2007, 10:06 PM

Since you have that big fat vacuum pump to vacuum the system afterwards, why not use regular compressed air and good ol'e soap and water to leak check? Are the any disadvantage or adverse effects for using compressed air?

Matt L · #10 07-02-2007, 10:33 PM

Quote:

Originally Posted by 85chedeng300D

Since you have that big fat vacuum pump to vacuum the system afterwards, why not use regular compressed air and good ol'e soap and water to leak check? Are the any disadvantage or adverse effects for using compressed air?

The disadvantage is that the oil is rather hydrophilic. You want to use something very dry.

pwogaman · #11 07-02-2007, 10:38 PM

Quote:

Originally Posted by 85chedeng300D

Since you have that big fat vacuum pump to vacuum the system afterwards, why not use regular compressed air and good ol'e soap and water to leak check? Are the any disadvantage or adverse effects for using compressed air?

I don't have a clean air compressor. Plus I wouldn't want regular compressor oil mixing with the new refrigerant oil. Not to mention the crud it would deposit in my new receiver/dryer.

Also, if you don't get the air out you will develop a new understanding of the term diesel. Air + oil (refrigerant oil will do) + pressure = diesel combusion

Neat idea, but I'll just stick with inert gases.

pwogaman · #12 07-03-2007, 11:25 PM

I'm absolutely convenced that an A/C pressure testing is the way to go! I pulled a vacuum (at 17.7 cfm) for over an hour and then let it sit for about 44 hours and there was no movement on the gauge the entire time - zero movement! From all appearances it would seem the system was ready for charging.

I went ahead and tried the argon/co2 pressure test. The most pressure I could get using the welding regulator was about 80 psig (I did not want to directly connect the tank to the a/c system because it would probably fail with 1,800 psi in it. Almost immediately I noticed a leak! In fact I even felt it, and that was at about 40 psig - granted it was on the high pressure hose where it fits to my guage manifold, but it was definitely there and I did not find it by almost 2 days of near perfect vacuum! I am certain it was not a result of any change to the manifold. In fact I did not even move it once when switching over from vacuum to pressure. As soon as I switched hoses I was able to finish the testing successfully - no leaks!

I pulled the system again to get the argon / co2 out of the mineral oil (that mix comes from the application of pressure that is essentially the same as scuba diving to about 120', deep enough to get the bends) and tonight I'll let the system hold the vacuum again. I might pull it again somemore before charging just to make sure I fully decompress the gas and don't give the system the bends, so to speak.

I've got a fresh batch of virgin R-12. I can't wait.

vstech · #13 07-04-2007, 10:54 AM

Yeah, it always amazes me when "professional" a/c techs "test" a system for leaks with vacuum... ABSOLUTE pressure diff in a PERFECT vacuum is only 14.7 psi to atmosphere... not much to deal with. and perhaps with a true vacuum gauge with digital micron readout, you may be able to detect a small leak, that leak would cause MOISTURE to be drawn into the system potentially damaging the dryer and contaminating the oil in the system. dry nitrogen/ whatever gas pressure is THE WAY to check for leaks!

pwogaman · #14 07-04-2007, 06:35 PM

I charged up this morning using my Robinair dial-a-charge. It is the first time I used it and it works very easily. It doesn't have a heater element so I just put the bottom of the device in a bucket of some hot water and that took care of it - the refrigerant easily transferred to the cold car just like it is supposed to. I believe I put in exactly the 2.9 pounds of R-12 and 6 onces of minieral oil required. The car is blowing cold, cold, cold!

I will cover the expansion valve after a few days of operation so I can first have an opportunity to check it for leaks. The I will also replace the underdash cover.

So far everything is working according to plan. I am happy about that.