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Subcooling and leak repair  Rate Topic 
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 Posted: Mon Nov 15th, 2010 07:43 pm
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johnbinsc
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Hi guys,
I think one of my Trane XL1400 2 ton split system heat pump units (installed 1999) is low on freon (R22), thus has a leak, probably slow.  This unit has two TXVs, one on the evaporator, one on the condensor.

The preferred method of charging is by measuring the subcooling in cooling mode. 

Question 1:  Are there any tricks to getting a good temperature measurement on the liquid line?  Can I get away with a standard instant read dial thermometer?  I was thinking about taping the thermometer shaft to the line and covering with some pipe insulation, but was wondering if there was some kind of good thermally conductive putty that I could use to enhance the thermal contact between the two.  Or is all that overkill?

Of course, now that it is November, finding a day above 65 deg F to do the subcooling measurement in cooling mode is not so likely.  I could also measure the subcooling in heating mode, but I don't have a chart for that. 

Question 2: Is it practical to set the charge on the system by using the subcooling in heating mode?
Question 2a: If so, do I measure the temperature at the liquid line exiting the coil in the air handler, or can I get away with measuring it as it enters the outside unit?
Question 2b: If so, are there charts for this?  If not, what value of subcooling is the target in heating mode? (cooling mode subcooling ranges from 6 to 11 deg F).

I will try to find the leak using a sniffer and/or UV (the system already has dye in it from when the first evaporator went bad in 2003).  If the leak is again in the evaporator I would rather try to use a leak sealer rather than replace the evaporator as the system is no longer under warranty.

Question 3:  Does anyone have experience with SureSeal and/or EasySeal?  Do they work?  Are there any negative consequences?  Is there any reason, besides the expense, not to add can of leak sealer to the system?

I know about needing to make sure there is no moisture in the system with EasySeal, but the system is still under pressure so I expect it is dry. 

And for the record, I just bought the kit to get my EPA 608 certification so I can do this in an environmentally sound and legal fashion.

Thanks in advance!

Last edited on Thu Nov 18th, 2010 02:03 am by johnbinsc

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 Posted: Thu Nov 18th, 2010 12:26 am
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AmTec Services



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There should be a heat cycle charging chart for that Trane. You will need a good thermo to charge correctly. An indoor outdoor thermo with a remote sensing bulb or thermister is ok in a pinch, but if your gona do it often you might as well get the right tools.

I dont like sealers, but thats JMHO.

..................AmTec



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 Posted: Thu Nov 18th, 2010 02:23 am
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johnbinsc
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Thanks for the response. Would I get the heat cycle charging chart directly from Trane, or is there another source? The service sheet has some heat cycle performance charts but I don't think that's what you are talking about. I assume the heat cycle charging chart is somewhat like the cooling cycle charging chart with bracketed subcooling target lines plotted versus a liquid temperature and a pressure.

I just bought a used Fluke 52 Series II digital thermometer on ebay to do the temperature measurements.

There is a long recent discussion of Cliplight Super Seal HVACR on hvac-talk.com with no clear conclusion. I guess I should find the leak first, see if it is repairable without replacing the evaporator, and if not, see how big it really is before making any decisions.

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 Posted: Fri Nov 19th, 2010 12:27 pm
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ACtechGUY
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As far as taking a liquid line temp goes , just tape your temp sensor to the liquid line near the condenser and insulate it for the most accurate reading.

As for Charging in heat mode..... There is no way to get a totally correct charge in heating mode. All you can get is " it will heat" charge. Heat pumps can only be accuratly charged in the cooling mode. If you have the service facts for that unit, then you have the charging instructions for that unit in the heating mode too.

About sealers... I have a test going on a 3 ton watersource heatpump for a server room with a tiny leak in the middle of Evaporator coil. I am hopeful that it will stop the leak, but I don't know yet.



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 Posted: Fri Nov 19th, 2010 07:37 pm
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AmTec Services



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AC tech guy;

What type of metering device is in that unit?



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 Posted: Fri Nov 19th, 2010 10:58 pm
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ACtechGUY
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It Is a ClimateMaster with a TXV. Why dooos u bee a askin'???........:headscratch:



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Don't know much. But learned early on, once you let the smoke out of a something electrical, you can never put it back in!!:oops:
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 Posted: Sat Nov 20th, 2010 01:03 am
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AmTec Services



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Interested in how leak stop acts with txv's and filter screens in front of them. Let me know how it works out. I've not used it in a r 22 system. Only is automotive, with disapointing results. But, I learned long ago I dont know everything and am willing to add to my arsenal anytime!:D

....................AmTec;)



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 Posted: Sat Nov 20th, 2010 02:04 pm
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ACtechGUY
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I can tell you , the stuff I used was a very thin liquid that when exposed to just air did not change in at all , it just stayed a liquid. All I can see is there is a reaction when this stuff combines with refrigerant and is then exposed to air.



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 Posted: Fri Aug 17th, 2012 07:11 pm
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johnbinsc
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I know this thread is very old, but since long term followup is of value in appliance repair, I thought I would supply an update.

So shortly after I posted last back in Nov 2010, I earned my epa certification, bought a 30 lb tank of R-22, and a few other minor tool upgrades.  After a few cycles of adding some freon and then having the unit crap out again after a few days, and finding evidence of a leak in the evaporator again, using both uv dye and a sniffer, I decided to try a leak sealer.

I opted for the Nu-Calgon AC EasySeal because I liked their "NASA uses it" marketing schtick.

First I charged the system using a rough subcooling metric in heating mode.  I ran a QuikAcid test and Quicklook moisture test first, which looked OK. Then I added a can of Nu-Calgon EasyDry just to be sure.  After running the system for 1/2 hour, I added a can of Nu-Calgon EasySeal.  I did a few things to make sure the evaporator saw plenty of moisture so the EasySeal had moisture to react with, since it was heating and not cooling season, but I don't know that it made any difference.  Over the next couple of days, I did more careful performance measurments, and topped up the freon according to the heating mode performance charts.  The heating mode was working great.  At mild outdoor temperatures (40F) I had nice WARM air from my upstairs AH.  Of course at <20F outside, it still sucked, but you can't beat thermodynamics.

It was my intention to go back in the spring and check the charge using the subcooling in the cooling mode but I never got around to it.

The system worked great for 18+ months then, in July 2012, one morning, no cool.  I didn't have time to look at it because I was going out of town right away so I just shut the system off at the Tstat, thinking the worst.  When I got back to it two weeks later, I found that the breaker on the outside unit had been tripped, and that the problem was a short in the sump heater (common problem with these units, I had already replaced the sump heater in the other identical unit).  So I removed the sump heater from the power, and since it was 80F ambient I just started it up and it is working great again.

So, long term followup says Nu-Calgon AC EasySeal worked great on my evaporator leak for 18 months so far.

I will follow up again next time something comes up.

One minor issue: When I started the unit up, there was a brief (2 sec) chugging sound from the compressor, which probably means there was freon in the oil since the sump heater had been off.  I was very surprised this could be a problem in the summer in SC, but I guess my understanding of the role of the sump heater was incomplete.  Possibly this is an indication that the unit might be somewhat overcharged, although I had gotten the impression that in fact heat pumps have a lot of wiggle room in the overcharging area because they have a large accumulator in front of the compressor. 

Fortunately, it did not BREAK the compressor, although whether there is any internal damage from this mistake time will tell.  Hopefully this will not taint the EasySeal long term test. 

I will be sure to replace the sump heater as soon as the weather cools a bit.  So long as the unit is running every few hours to cool the house, it doesn't need the sump heater because the compressor takes a very long time to cool down between on cycles.

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