# What are the symptoms of a bad thermal expansion valve TXV?



## aluminumwelder (Apr 3, 2015)

Just had a tech install a TXV on my 4 ton indoor coil. 
He didnt' want to use nitrogen because he told me that it would cause bubbles in the solder joint and thus have leaks down the road. 
It kind of made sense and it was hot as hell in the attic to be arguing about this, but I still insisted he use Nitrogen. After all he had a tank in his service van and it only took 5 minutes to hook up! However I don't think he used nitrogen outside on the compressor valves. 

He also insisted on putting in the valve ( that tiny valve that looks like it came off a bicycle wheel stem), even though I do not see any reason to have it in, since the fitting presses down on the valve and keeps it open 100% of the time.

So I've read that dirt and grime from brazing done with out nitrogen can clog up the TXV valve down the road. Any truth to that and if so what should I look out for?

tech told me that TXV valves fail due to air filters not being cleaned. 

Lastly how should the TXV (which is external to the coil in the attic) be insulated? Right now there is some self adhesive black foam wrap around the actual valve and the bulb and the rest of it is naked. it's kind of hard to insulate due to it's coil/wires I was thinking a bunch of shredded fiberglass made into t ball around the whole thing and then taped up, it would look ugly but protect it from attic, heat.


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## beenthere (Oct 11, 2008)

The foam wrap insulation works fine.

Dirty filters don't harm TXVs.

If the joints are grossly over heated, the oxidation can clog a TXV.


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## yuri (Nov 29, 2008)

Where did he stick that tiny valve in? It is called a schraeder valve. (Need a pic).

The small line on the TX valve is a equalizer line and should not have a schraeder in as there is nothing to press it in. Refrig gauges have a tit which pushes it in. The equalizer line is just a small line with a flare nut. It may not work now if that valve is in.


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## aluminumwelder (Apr 3, 2015)

Yes it is the small line with the flare nut, but it does depress the valve some how because I put the small line on the coil while it was still pressurized with nitrogen from the factory and it leaked out the nitrogen as I turned the flare nut. Of course he did not use the same valve and brazed a new valve . The one he put in might be slightly different and might not be depressed so now I'm just wondering whether the system is working at 100% or if the $100 TXV is just sitting there doing nothing? anyway to check?

I just dont' know why he put it in. It serves no purpose and can only be one more part that could potentially go wrong. 

I honestly do not understand TXV. Looks like they somehow equalize pressure between high and low side as needed.


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## yuri (Nov 29, 2008)

The reason some people put them in is to check the suction pressure at the coil. I always do it outside but some people apparently do it inside ( amongst other things, wink wink).

As far as I know the only way to depress a schraeder valve is with a refrig house as it has a tit inside. If someone else can verify it may be working for you so be it but I highly doubt it. Does not make sense they would invent such a device on that line when all you need to do it throw away the schrader valve.

It needs to work or the compressor will have one he*ll of a time starting after a power failure or on very hot days if the pressures have not equalised. That is very bad for compressors and can stall them and shorten their life etc etc.

It also allows the valve to modulate properly. Need to Google: thermostatic expansion valve and see how they work. Sporlan and Emerson etc have some info.

I hate to say it but there are a lot of "techs" out there that are not as highly trained as others. In my experience very few young guys take anything seriously besides their I Phone and girlfriend and social life and sports pools etc. I have trained and tried to train a lot of apprentices and they keep answering their phone and texting instead of learning their trade. Makes no difference to me when they leave me and struggle thru service calls when they could have learned when they had the chance to ride with a Journeyman.

Just the way it is.


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## user_12345a (Nov 23, 2014)

It needs to work or the compressor will have one he*ll of a time starting after a power failure or on very hot days if the pressures have not equalised. That is very bad for compressors and can stall them and shorten their life etc etc.

^aren't there non-bleed liquid solenoids and txvs spefically to prevent equalization and reduce cylcling losses?


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## yuri (Nov 29, 2008)

user_12345a said:


> It needs to work or the compressor will have one he*ll of a time starting after a power failure or on very hot days if the pressures have not equalised. That is very bad for compressors and can stall them and shorten their life etc etc.
> 
> ^aren't there non-bleed liquid solenoids and txvs spefically to prevent equalization and reduce cylcling losses?



There are TXs that are non bleed and some are bleed. All depends on the valve and we don't know what he has.


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