# 3/4" vs 7/8" vapor line



## yuri (Nov 29, 2008)

the reason the manufacturers not us Pros want the lineset the correct size is for proper velocity of the vapor which gives you proper oil return. improper oil return will slowly kill the compressor and technically could void the warranty. you may get away with it but only the design engineer for that brand would be able to approve that setup and I doubt they would. I also like clean new copper for sanitation reasons even though some guys flush the old lines new is always better.


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## beenthere (Oct 11, 2008)

3/4" is fine for a R410A 3 ton. 

A 7/8" vapor line would give, you a capacity loss of 417BTUs per 100 foot of line set.
A 3/4" vapor line would give you a capacity loss of 921BTUs per 100 foot of line set.

3 ton unit 7/8" velocity is 1047 FPM
3 ton unit 3/4" velocity is 1454 FPM


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## yuri (Nov 29, 2008)

when it gets to the 50 foot length I would be more concerned but as theory I always follow the manufacturers specs and used 3/4 not 5/8 on my 2 ton Armstrong as that is what they wanted. bigger is better with lines.:yes:


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## beenthere (Oct 11, 2008)

yuri said:


> when it gets to the 50 foot length I would be more concerned but as theory I always follow the manufacturers specs and used 3/4 not 5/8 on my 2 ton Armstrong as that is what they wanted. bigger is better with lines.:yes:


Actually, 3/4" vapor line is bigger then what should be used on a 2 ton for good oil return. The velocity is only 970 FPM. The manufacturers often use a vapor line size that gives them the 13 SEER rating, but is not best for oil return.

If the condenser is not above the evap, 3/4" is ok. But if the condenser is above the evap by more then 6 foot or so. Then 5/8" is better for oil return, and only loses 776 BTUs per 100 foot of line.

2 ton 5/8" vapor line, 1449 FPM, 776 BTU capacity loss.
2 ton 3/4" vapor line, 970 FPM, 295 BTU capacity loss.


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## raylo32 (Nov 25, 2006)

Thanks for the interesting discussion, guys. Very informative. BTW, I just went out and cleaned my condenser coil using your simple green method and dropped my head pressure by 50 psi, low pressure by 8 psi, and vent temps by 3 or 4 degrees. I also adjusted the charge back to the label plate SC value (took 1/2# or so) so hopefully I'll have full capacity and good performance in the current heat wave. Yikes, that coil was really dirty. And maybe I just bought myself another couple of good years out of this unit.


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## beenthere (Oct 11, 2008)

Was the condenser coil completely dry before you added more refrigerant. If not, recheck it.

Lots of condenser coils don't look real dirty. But when you clean them, you get a lot of dirt that you couldn't see out of them.


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## raylo32 (Nov 25, 2006)

I let it run a good 10 minutes so pretty sure it was dry and stable. But I'll give it a quick check later to be sure. I am amazed the difference the cleaning made. I won't let it go so long again.


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## beenthere (Oct 11, 2008)

raylo32 said:


> I let it run a good 10 minutes so pretty sure it was dry and stable. But I'll give it a quick check later to be sure. I am amazed the difference the cleaning made. I won't let it go so long again.


A chemical cleaning in the beginning of the year, and just a water hose off in the middle of the cooling season works wonders.

I usually give them a good 15 to 20 minutes, before I decide if the charge is ok or not after I wash a condenser coil. This gives time for all the water on the coil and the surrounding area to evaporate. So that there is no influence from the washing of the coil by water evaporation.


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## yuri (Nov 29, 2008)

the other reason I like larger lines is we have all seen where guys hand bend the suction line and sometimes start to kink it. so your 3/4 line becomes 5/8 and that is were the problem starts. if it has no kinks then it will work but as Been said you lose a bit of efficiency. I am a perfectionist as much as possible but if the ceiling is plastered then would reuse the lines if not kinked. it is a logistical nightmare but in the future the manufacturers could start to void warranties if the lines are not to their spec. very hard to police but anything is possible. most compressors fail from being run low on Freon, freezeups from poor airflow, overworked from a dirty condenser, power surges and cheap construction in my experience.


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## raylo32 (Nov 25, 2006)

It ran a good 30 minutes during the process since I just added a puff at a time then gave 5 minutes to stabilize each time. Not on the clock here.... The other benefit I am already seeing with the colder evap coil temp is a several % drop in my indoor RH. I'll follow your advice on the cleaning regimen from now on!

One other thing that worries me that might drive the need for a new lineset in a future upgrade is the physical arrangement of the indoor coil connections. Unless the new ones are pretty much exactly where the current ones are the lineset would need to be extended... or if that is not possible, replaced ($$$). I have never seen HVAC/R copper tubing offered in small repair lengths. Not sure how you could have something like that and keep them charged with nitrogen until use.


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## beenthere (Oct 11, 2008)

Soft rolled copper is not charged with nitrogen. It is cleaned and dehydrated. We don't throw away a roll because we only used 30 foot of the 35 foot. We seal the ends, and use it on some other job. Often, to extend a line set.


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## yuri (Nov 29, 2008)

Hence the 500 micron vacuum AND a proper additional filter drier if it does not have one internally. some el cheapo brands/units expect U to supply your own and add it externally.

R U planning to do the job yourself? If not then the price of the lineset is included in the install (unless you really haggle it out) so it is not a price concern anyway. Not likely the new coil fittings will line up but sometimes adding a few elbows will do it.


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## raylo32 (Nov 25, 2006)

It is still hopefully a couple years off at least. I might DIY... I replaced the evap coil myself a couple years ago when I put in the furnace and this wouldn't be much more difficult.

It would be easiest to drop in a dry-ship R22 condenser and I have a jug of R22 I bought before the prices went nuts so I have plenty. But I'd like a nice 2-stage condenser and I haven't seen anything but basic low efficiency single stage R22 units on offer.... so may be driven to R-410 space. But that creates more issues with the lineset and evap coil. I could swap the TXV in my current coil for a 410 TXV (more work)... or just get a new 410 coil, a much more expensive option.

While a contractor bid for doing the job could surely include the lineset, I bet it wouldn't include all the drywall r&r and painting. That would be a real mess and very expensive... or a major DIY PITA. I would probably need to make several large access holes in the ceiling and a couple more in the outside wall. Then patch it all up, tape, mud, sand, paint. Uggghhh.

And it's interesting about evap coil connection locations. There don't seem to be standards for this but when I needed an evap coil to replace my leaking Bryant coil I was able to find a Carrier unit. Being the same mfg the connections were configured the same and it matched right up. So no need to extend or reroute the lines. I suspect that the new Bryant/Carriers are the same configuration so those would be first on my list if I were to replace the coil. 

In any case barring a sudden failure I think I have some years to go. At some point I might get nervous enough about it to replace it on spec before it fails. But I am not there yet. And I'll try to do better at keeping up with the cleaning.


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## beenthere (Oct 11, 2008)

York CZH036 2 stage A/C line set is 3/8 and 3/4.


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## Doc Holliday (Mar 12, 2011)

whatever the condenser size is is what I use.


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## yuri (Nov 29, 2008)

York makes a good unit but if U want a 2 stage setup you need a furnace with a 2 stage capable circuit board hookup for the extra speed. need a Y1 and Y2 with any brand. does yours have that. the newer Carrier and I imagine Bryant coils have the TX valve mounted internally and sit inside the ductwork not an added TX valve outside.


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## raylo32 (Nov 25, 2006)

Thanks, BT, that York condenser would be a perfect match for my Hamilton/York 2 stage variable speed furnace (that I installed with you and Yuri's help for figuring out the venting). So maybe I'll have a fall/winter project. ;-)

Yuri, my Carrier coil is about 2007 vintage CNRVP with the tin-plating. I didn't install it until 2011. The TXV is visible but it doesn't have a threaded eq line connection. I actually bought a R410 txv back then in anticipation and have it in my HVAC parts box but my Bryant R22 system keeps on going. I guess I'd have to cut off/crimp/braze shut the existing eq line, then punch and braze in the new one. Otherwise the TXV bolts right in. That doesn't look to be too difficult.

But I dunno. My current system is still working fine so I am in no rush. But it's good to keep up on the options...


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## yuri (Nov 29, 2008)

In 2007 was it a 13 SEER coil or lower? May not be a good match now if it is lower.


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## beenthere (Oct 11, 2008)

In 2006 all conventional equipment made for use in the USA had to be a min of 13 SEER.


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## bobelectric (Mar 3, 2007)

beenthere said:


> Soft rolled copper is not charged with nitrogen. It is cleaned and dehydrated. We don't throw away a roll because we only used 30 foot of the 35 foot. We seal the ends, and use it on some other job. Often, to extend a line set.


 Shop at the recycle yard on a Friday afternoon.


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## raylo32 (Nov 25, 2006)

Good point Yuri... I am not sure what the coil's SEER is. I'll have to take a close look at the label plate to see what info it provides, at least a mfg date. I wonder if my memory is accurate. ;-)

Good tip, Bob, to look for scraps of tubing in a recycle yard.. or I guess at a scrap metals dealer. It's strange that 3/8 is readily available in short coils of 10' but the bigger stuff seems to only come in 30' or longer coils.... at least from what I can find online. But I wouldn't need any if I kept my existing coil and went with a 3/4" condenser.


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## yuri (Nov 29, 2008)

1/4 and 3/8 are very common for plumbing and oil burners etc (small jobs) whereas the 5/8 and up is only for AC and BBQs/furnaces etc which would involve longer runs or a lot of coupling together of those 10 ft rolls.:no:


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## raylo32 (Nov 25, 2006)

Agree it certainly wouldn't make sense to couple 10' rolls! That would be silly when they are readily availble in full lengths. Just might be nice if they sold them for those times when we maybe need a few feet for an extension or whatever. Some of us who don't have access to job leftovers!

On another topic related to upgrades... one that probably has been discussed before... I think R410a is itself slated to be replaced due to its high GWP. I don't know when (soon?) or with what (407c perhaps?) but thinking my R22 system might last until that occurs and maybe I can skip the 410a era entirely.




yuri said:


> 1/4 and 3/8 are very common for plumbing and oil burners etc (small jobs) whereas the 5/8 and up is only for AC and BBQs/furnaces etc which would involve longer runs or a lot of coupling together of those 10 ft rolls.:no:


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## yuri (Nov 29, 2008)

Ya never know. Bryant in my experience is the higher end of the Carrier family and their ACs were/are very well built (except for the builders grade) so I suspect it could go 25 yrs, depends on your climate and the number of running hours. only so many of them per compressor.


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## raylo32 (Nov 25, 2006)

It is builder's grade... well, I assume it's builder's grade since my builder didn't splurge on anything as far as I can see. But most folks in my neighborhood still have the originals so the condensers seem to be pretty durable. Hope I didn't take too much life off of mine by running 275 psi for awhile. Now back to ~215-220 post-cleaning.

I have a friend that lives in a 100 year old townhouse down in VA and he has a 1974 vintage Carrier split A/C that he claims still works fine. He says the house's ducting predated the a/c install so it isn't really balanced that well. It doesn't get much use as he also has a couple of strategically placed window units that he uses mostly. So maybe his Carrier will go another 25 years??


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## FixitDragon (Feb 9, 2011)

I have been wondering some of the same. I am looking into the eventual replacement of my AC and the possibility of reusing the lineset. Existing is 3/8" and 3/4", and new 410a 3 ton are 3/8" 7/8" My existing lineset is longer, around 50ft and is run through the unfinished attic. Sounds like it would be best to replace it. 

Speeking of longevity, I have the original Westinghouse installed in 1981 (32 years old) It still runs like a champ. 18-20° delta T, and can keep the house 25° below the outside temp. I usually leave it set for 78°. I just wish it had a little more capacity. Seems the design temp for my location was 100°, but we have a lot of days over that and it just can't maintain the set point. In addition to the age, the cost of electricity in my area makes the return on investment for a 16SEER single stage and basic furnace about 3 years.


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## yuri (Nov 29, 2008)

the reson some of those old birds lasted a long time was very simple. They had a GOOD heavy duty compressor and if you were real lucky the one made by Tecumseh. OLD old company who makes great small engines for snow blowers etc. Mom's old genuine Keeprite (Canadian made) is 33 yrs old and may look real ugly but still gets you were you want to go and has the Tecumseh compressor. They DO NOT make that quality anymore.:no:

In California I would want the Lennox 25 SEER unit, probably pays for itself in 6 months.:thumbsup:


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## beenthere (Oct 11, 2008)

You can gt a 3/8X3/4 lines et in a 15 foot length.


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## beenthere (Oct 11, 2008)

FixitDragon said:


> I have been wondering some of the same. I am looking into the eventual replacement of my AC and the possibility of reusing the lineset. Existing is 3/8" and 3/4", and new 410a 3 ton are 3/8" 7/8" My existing lineset is longer, around 50ft and is run through the unfinished attic. Sounds like it would be best to replace it.
> 
> Speeking of longevity, I have the original Westinghouse installed in 1981 (32 years old) It still runs like a champ. 18-20° delta T, and can keep the house 25° below the outside temp. I usually leave it set for 78°. I just wish it had a little more capacity. Seems the design temp for my location was 100°, but we have a lot of days over that and it just can't maintain the set point. In addition to the age, the cost of electricity in my area makes the return on investment for a 16SEER single stage and basic furnace about 3 years.


Add insulation to the attic. See about sealing the house better. might be able to decrease your heat gain by 6,000 BTUs or more.


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## sktn77a (May 11, 2009)

FixitDragon said:


> I have been wondering some of the same. I am looking into the eventual replacement of my AC and the possibility of reusing the lineset. Existing is 3/8" and 3/4", and new 410a 3 ton are 3/8" 7/8" My existing lineset is longer, around 50ft and is run through the unfinished attic. Sounds like it would be best to replace it.


Look at the installation manual of your new condenser. It will tell you exactly what the recommended liquid and vapor line sizes for different line lengths and condenser/evaporator vertical separation are. Even if you exceed the length of at 3/4 vapor line, you should only loose a little efficiency (maybe 0.5% -1.0% per 20 feet). 

It should all be there in the manual.


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