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Line set diameters


mgbinspect
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OK, I suspect this has probably been addressed before, BUT WTH...

This is something I only see a couple times a year and I always call it out - line set diameters that don't match the diameter of the evaporator or condensing unit coil tubing.

It seems that it would logically HAVE to affect some aspect of heat pump or air conditioner performance since the volume of the tube is different - maybe the velocity at which refrigerant flows to meet compressor demand is increased or pressures can't be achieved or maintained... That's why I'm posting this.

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Again, I do always call it out and refer folks to a HVAC specialist, but I really want to hear from the HVAC trained brain-trust technically what is affected and why?

Lay it on me!

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I'll take a stab at it, my friend.

The smaller line is the liquid refrigerant line. It carries liquid refrigerant to the cooling coil (summer mode) for expansion into a gas. That's the principle of refrigeration systems...the change in phase from a liquid to a gas is accompanied by a dramatic reduction in temperature of the refrigerant and that drop in temperature is employed to cool the house. This change in phase from a liquid to a gas is accomplished by placing a restriction in the flow of the refrigerant that causes it's pressure to drop to a low value. Therein lies the problem with undersized liquid refrigerant lines...there is pressure drop within those lines also and if the line is too small for too long, the pressure drop may be great enough to result in a partial expansion of the liquid refrigerant (bubbles in the liquid) inside the liquid line before it even reaches the cooling coil. The result is less btu/hr removed from the house. How do we know if expansion is taking place within an undersized liquid line? Feel it. If it's cooler than usual or cooler as it approaches the cooling coil, it's expanding and it's always a problem when this happens.

Marc

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So then, do you feel that it's legit to always make a Pretty Big Deal about this condition? And, why the H*LL do alleged licensed professional HVAC contractors pull this shite?

I suppose the contractor was too lazy to change out the line set? or, it was the only one he had with him and just didn't care to go back to the shop for the right set?

It's really annoying... [:-banghea

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I see undersized liquid lines on smaller systems once in a while. I check them and seldom detect bubbles in the liquid. Experienced AC guys can usually 'feel' bubbles by touch, at least the deaf ones with their redirected senses can. I don't bother with mentioning it to the client, but I'd suggest that if you do see undersized lines (1/4" line on a crimped or reducer-connected 3/8th appliance connection) on any residential system larger than 2 1/2 tons, call it, regardless of whether you feel bubbles, cooler lines or nothing.

Marc

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HVAC contractors often try to scare customers into parting with their money to complete unnecessary 'repairs'. I had one today, poor guy didn't think this inspector would know anything about refrigeration...but that's another story.

Marc

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Well, but it's not always wrong. It looks like the reduction in your photo is from 3/4" to 5/8", which is sometimes necessary due to the refrigerant line lengths and/or the elevation differential between the condenser and the evaporator coil. I'm including a link that should prove helpful and explain things much more succinctly than I could. Check out page three, specifically "Line Sizing."

Oftentimes, but of course not always, altering the refrigerant-line size is a sign of competence and responsibility, rather than the opposite

http://www.colemanac.com/PDFFiles/247077-UAD-H-0209.pdf

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Bain, I guess it's difficult to gain any perspective from the photos. The smaller line diameter is probably no more than maybe 3/16" to 1/4" - as small as I ever see... and it is on a 1.5 ton unit, if that helps. I'll check out the link.

I've just never known for certain if the line diameter of the coil is "the gospel", or just the largest recommended diameter, but using a smaller line diameter can be OK.

I'm afraid I didn't remove insulation to check the suction line diameter to see if it is also undersized, and kinda wish I had now just for further discussion's sake.

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Client's AC guy came out while I was still on the job to check a furnace issue that I had called out. He started out predictably and agreed that the entire HVAC system needed replacement due to age and rust in the fire chamber that buried nearly half the burners. But then he went on to how closet units (existing furnace was in a closet) suck up more dust from the floor than attic units. That was his argument for abandoning the closet and installing in an attic that was no more than 5' high at the ridge. But I suspected that he simply wanted a clean slate to install his new system and didn't want the trouble of removing a gas powered furnace from a closet (cooling coil was behind the wall framing above the top of the door). It means more money for him and less trouble, but I've busted my knees servicing furnaces in hot, cramped attics with undersized air returns because of the lack of space for prefabbed ductwork so I went back and forth with him for a short while before the client interrupts, takes position besides me and says 'closet'.

That client was a student in my class for first time homebuyers Monday of last week.

Marc

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Good for you. It's not altogether the same, but in my cover letter I tell people, "If you discover a condition that you feel may have been overlooked, CALL ME FIRST before you do anything, because I want to make certain: 1. It's legit. 2. You don't get taken." And, over the years, the folks that didn't call me got taken pretty badly (usually over non-events) and the people that did call me avoided wasting a lot of money and thanked me for it. It's pretty sad how willing folks are to take another's money.

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I'm with Bain on this one, It is not always wrong.

Now if you see a hunk of tubing half the size of the line and unit size stuck in place of where the drier used to be that is an obvious hack job, then call it out.

On the other hand if the line set is one size larger or smaller than the condensing unit stubs then it may be right.

I personally don't get excited unless the unit is not cooling properly.

But here in the land of perpetual A/C, it is rare that a line set is undersized since we try to wring every BTU out of units and they get a good test every season.

Without the manufacturer specs on the individual unit, line set length, and diameter you are pretty much shooting in the dark.

Given your photo of this specific installation it looks like the cut out a filter drier and replaced it with the first hunk of pipe off the truck. Ugly and not correct but unlikely to cause any real difficulty given the short length of the smaller tubing.

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I'm no AC expert but I think that may be a problem. I am running into alot of new systems with 410 that are using the same lineset that was for the old R22 system. 410 needs a larger line, but sometimes it is a real PITA to change the lineset so they end up with a 410 system with a 3/4 inch line. The efficiency will suffer.

You can not reuse the lineset from a 22 unit on a 410 unit period. The oil from a 22 system is not compatible with a 410 system.

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I had read a post on another site that refers to some Techs washing out the existing line-sets and using them for R410. Probably not the correct thing to do, but I guess that there are people doing that. Also said something about remetering the system as well.

Did they say how the techs washed out the lines? R-11 was used all the time for cleaning up after a burn etc... but that was one of the first refrigerants to go due to CFCs.

What matters, in the end, is what the manufacture mandates and not what a tech improvises.

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I had read a post on another site that refers to some Techs washing out the existing line-sets and using them for R410. Probably not the correct thing to do, but I guess that there are people doing that. Also said something about remetering the system as well.

Did they say how the techs washed out the lines? R-11 was used all the time for cleaning up after a burn etc... but that was one of the first refrigerants to go due to CFCs.

What matters, in the end, is what the manufacture mandates and not what a tech improvises.

Exactly, and why would some dipsquat risk damaging a new condenser by not following the manufacturer's requisites? Not to mention that said dipsquat will be able to charge his customer for parts and labor associated with installing the new refrigerant lines and increase the per-job profit.

It'll be interesting to see how well R410 works in the real world. The stuff is under so much more pressure than R22, the simple act of removing old-style gauges can release enough refrigerant into the air that the condenser winds up being undercharged.

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It'll be interesting to see how well R410 works in the real world.

I've got one, a Carrier, I'll keep you advised.

It comes with the new Carrier, noise dampening, feature (oh brother). It's a insulated jacket that covers the compressor. I'm sure without it though the compressor sounds like a jack hammer with the pressures they run now. After three or four years, in the outdoor elements, the jacket should be in fine shape too.

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I replaced my own central HVAC with an R-410 based AC/ electric heat system 2 years ago.

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Both inside and outside units are the quietest I've experienced of any AC I've ever come across. No factory jacket on my compressor. Hasn't given an ounce of trouble yet. As for losing gas when you connect or disconnect the guages, EPA has required quick connect devices for quite some time now. Never liked 'em but supposed to use them.

Marc

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I also switched from an R22 to a 410A system. A top of the line Carrier. They cleaned the lines, didn't change them. It been going on 2 years, the system works great, no problems at all. The 2 stage is so much nicer than the old single stage, heating and cooling is much more even and way cheaper to run. So, yes, you can use the same lineset.

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