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Old 04-03-2009, 08:56 AM   #1
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Finding A/C System leak


During a recent checkup, my mom's Lennox 10 SEER HS29-261-2P 2 ton with Armstrong CAU24-1 indoor coil has developed a leak after 13 years of perfect service.

I confirmed very low refigerant with low psi on both high and low sides. As I recall the low side was 0 and high 60.

I've charged to 200 PSI nitrogen pulled back the insulation and checked every joint with bubbling solution including the schrader valves. I've been unable to check most of indoor coil and get inside the outdoor unit to check the compressor. I left the gauges on and after 3 days now see at least a 10-15 PSI loss.

Unfortunately I'm not the most experienced in finding leaks, but this is looking like a very difficult leak to find.

My next thought is to evacuate, fill with small amount of r-22 and check with a leak detector, but given I've lost so little nitrogen, I'm not so sure this will pan out. Alternatively, I've also been told I could safely charge to 300 PSI since the coils are factory tested to 350.

What would you try next? Any thoughts or suggestions are welcome.

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Old 04-03-2009, 11:02 AM   #2
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Finding A/C System leak


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Originally Posted by myhvachelp View Post
During a recent checkup, my mom's Lennox 10 SEER HS29-261-2P 2 ton with Armstrong CAU24-1 indoor coil has developed a leak after 13 years of perfect service.


If you have narrowed it down to the indoor coil.. No need to locate . Just replace the coil If you haven't pull the coil & nitrogen test the coil

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Old 04-03-2009, 11:06 AM   #3
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Finding A/C System leak


NEVER put more than 150 psi in a R22 system! The compressor on the low side is designed for 150 psig and may be damaged at any higher pressure. Look at the rating plate info with the model # for design test pressures. The nitrogen pressure may vary slightly with changes in indoor and out door temp. You do have a leak but would need to use some R22 and a leak detector to find it. If it took 6-8 months to leak out and it holds about 5 lbs/80 ounces that is 10 oz/month which is a very small hard to find leak.

Last edited by yuri; 04-03-2009 at 12:01 PM.
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Old 04-03-2009, 11:16 AM   #4
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Finding A/C System leak


I don't know what's wrong with the galvanized metal on these newer coils .. They seem to rust away quicker than they did in the older coils. I have cleaned some that have been for 20 yrs & the galvanized metal looks almost as good as the day it was installed.. I have cleaned some that have only been in a few yrs & it looks like the metal has almost rusted away
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Old 04-03-2009, 11:43 AM   #5
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Finding A/C System leak


is the piping from the condenser to the evap hard copper or soft(as in rolled out)if hard check the line runout from the condenser into the house.might be a coupling/elbow showing oil residue.soft copper is usually connected at the condenser and run right into the evap with no fittings.that 200 PSI nitro'd mixed with the balance of the charge left in the system when you went to leak check,and if the outside temp was lower then when you read the 200 it can change with the sun hitting the condenser with a minimal pressure drop or rise.a good vacuum run and micron test(if you have one) or just use that suction guage for an overnight sit.check your guages with a vacuum test before putting it on the system if your guages/hoses leak your going to go in cicles there.YES you can go to 300-400 PSI to test the system with a nitro/freon mix to leak check if the vacuum drops bigtime within an hour after pulling it.to leak check from a vacuum add freon gas on hi/lo sides let it equalize then add the nitro to boost it.take a spray bottle with dishliquid and water and spray 4 rows of the condenser from the bottom,and any elbows you can access..check the compressor terminals for oil residue.if you pull a solid VAC somebody clipped the freon to get HIIIIIIIIIII
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Old 04-14-2009, 02:10 PM   #6
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Finding A/C System leak


Thanks for all the responses.

As an update I charged the system to 300 psi, got a Tif 5550A leak detector and began sniffing around. After many hours with no signs of oil residue it looks like the leak is in the outdoor unit, on the end of the coil with the 180 elbows around a bracket that holds the coil assembly to the sheet metal. I've not been able to pinpoint the exact spot due to a windy day, the bracket and maybe the leak being below and behind the bracket or a fin. But the leak detector goes off regularly in that area.

After some research it would not be cost-effective to replace the coil assembly with new due to the high cost, so my options are to find and fix or replace the entire outdoor unit.

Since Mom doesn't want to spend big bucks, I will try to find the leak. Any ideas on how to find a really, really (did I mention really) small leak is greatly appreciate. Thanks again, this one's for mom.
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Old 04-14-2009, 02:54 PM   #7
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Finding A/C System leak


Cover the unit with a large tarp while you are sniffing around so you get a better concentrated result. Try use Calgon/Masters gas leak detector soap or the clingy green gas leak detector soap. Even a tiny leak will show up with that Calgon stuff. Beware some electronic leak detectors can be fooled by liquids or other fumes/guck. I use a Bacharach type which looks for different ions rather than the freon itself. I have had great success with the Calgon soap.http://www.nucalgon.com/assets/prodlit/3-111.pdf


Good Luck

Last edited by yuri; 04-14-2009 at 02:57 PM.
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Old 04-14-2009, 03:00 PM   #8
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Finding A/C System leak


Sometimes, very small leaks are impossible to find....good luck. You may spend many,many(did I say many?) Hrs and still not find it
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Old 04-14-2009, 03:02 PM   #9
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Finding A/C System leak


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Originally Posted by yuri View Post
Cover the unit with a large tarp while you are sniffing around so you get a better concentrated result. Try use Calgon/Masters gas leak detector soap or the clingy green gas leak detector soap. Even a tiny leak will show up with that Calgon stuff. Beware some electronic leak detectors can be fooled by liquids or other fumes/guck. I use a Bacharach type which looks for different ions rather than the freon itself. I have had great success with the Calgon soap.http://www.nucalgon.com/assets/prodlit/3-111.pdf


Good Luck
Thanks. That's the stuff I've been using. I didn't think of the tarp idea, but I like it! I have some clear plastic drop clothes I can use so I still have some light.

Any other ideas are appreciated.
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Old 04-14-2009, 03:48 PM   #10
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Finding A/C System leak


When you put that soap on you have to stare at the area for at least 1 minute to watch for tiny bubbles. The key to success is not rushing. It runs off so reapply liberally. Get some small flex head inspection mirrors also. An electronic unit will only narrow down the search.
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Old 04-14-2009, 04:22 PM   #11
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Finding A/C System leak


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When you put that soap on you have to stare at the area for at least 1 minute to watch for tiny bubbles. The key to success is not rushing. It runs off so reapply liberally. Get some small flex head inspection mirrors also. An electronic unit will only narrow down the search.
Yes, that is what I thought. The detector will only get me so close, and the rest I will need to do with soap bubbles.
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Old 04-21-2009, 07:58 AM   #12
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Finding A/C System leak


Good news! I found the leak!

It is on the high side where the compressor 3/8" piping connects to the coil. It looks like a shoddy factory braze because the leak is on the bottom of the joint, leaking around the solder where the solder was not properly sucked into the joint.

Even better news it is definitely repairable. The joint is up high, very accessible and not near anything else that could melt.

I would like to take a shot at brazing/rebrazing this joint. From some of the soft soldering I've done and all the reading I've done, the tools I can get, I think this is doable, especially since I plan to practice on a few joints before tackling this.

So if anyone can guide me, I'd appreciate it.

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