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Old 07-07-2013, 09:09 AM   #1
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3/4" vs 7/8" vapor line


I am going on 18 years with my 3 ton Bryant R22 condenser (replaced the evap coil a couple years ago due to slow leak). Still working fine but I am looking ahead to the inevitable replacement in a couple of years.

My lineset and condenser and evap coil connections are 3/4" but I see that most if not all R410a equipment of that size uses a 7/8" vapor line. The lineset is about 30 feet total running through a finished ceiling and down a finished exterior wall and out the back of the house. Replacing the lineset would be a major PITA and large expense.

The question is can this lineset be used on equipment calling for 7/8"? I am guessing this would just cost a little bit of efficiency but shouldn't stress or damage the equipment? Or do you contractors and mfgs insist on including a lineset upgrade in these cases?

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Old 07-07-2013, 09:25 AM   #2
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3/4" vs 7/8" vapor line


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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Old 07-07-2013, 09:33 AM   #3
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3/4" vs 7/8" vapor line


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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Old 07-07-2013, 09:38 AM   #4
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3/4" vs 7/8" vapor line


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.
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Old 07-07-2013, 09:55 AM   #5
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3/4" vs 7/8" vapor line


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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.
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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Old 07-07-2013, 10:33 AM   #6
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3/4" vs 7/8" vapor line


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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Old 07-07-2013, 10:37 AM   #7
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3/4" vs 7/8" vapor line


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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Old 07-07-2013, 10:53 AM   #8
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3/4" vs 7/8" vapor line


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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Old 07-07-2013, 11:00 AM   #9
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3/4" vs 7/8" vapor line


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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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Old 07-07-2013, 11:22 AM   #10
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3/4" vs 7/8" vapor line


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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Old 07-07-2013, 12:02 PM   #11
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3/4" vs 7/8" vapor line


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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Old 07-07-2013, 12:31 PM   #12
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3/4" vs 7/8" vapor line


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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Old 07-07-2013, 01:06 PM   #13
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3/4" vs 7/8" vapor line


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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Old 07-07-2013, 03:52 PM   #14
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3/4" vs 7/8" vapor line


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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Old 07-07-2013, 05:57 PM   #15
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3/4" vs 7/8" vapor line


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

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