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mgbinspect

Undersized Line Sets

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OK, I'm sitting down to write up this morning's inspection.

we've been down this road some before, but it's come up again, and it's high time for me to actually hammer out a good boilerplate comment about this condition:

If we think back to our basic geometry days, we'll recall that a small change in diameter results in a huge change in volume. It's that truth that always has me worried when I see a new condensing unit hooked up to a line set that doesn't match in diameter to the unit. I don't know if they just re-used the original line set or just threw in what they had on the truck, but the wet line is easily 50% smaller than the line coming out of the condensing unit.

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So, I"m teeing this up for the braintrust to chew on, while I write up the rest of this report hoping that some of you HVAC sevants will chime in and offer specifically what you would write about this. I'm going to say something, but it would be nice to have some qualified help in putting together a good permanent statement about it.

Thanks in advance for your thoughts.

Shoot!

Oh, BTW, don't ya just love the way the master HVAC contractor left the new system literally sucking in unfiltered and unconditioned air from the crawlspace? This kind of conscientious workmanship always gives me an especially warm and fuzzy feeling. [:-irked][ It really demonstrates just how much the guy cares about his customers, eh? V]

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You really need access to the installation manual to know what's necessary. The liquid line is typically always 3/8", but the suction line can vary in diamter depending upon the size of the condenser and the length of the lines.

It looks like the liquid line in your photo is 3/8", which would make it okay.

I did a quick Google and found this generic diagram that sort of explains what I'm talking about.

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You really need access to the installation manual to know what's necessary. The liquid line is typically always 3/8", but the suction line can vary in diamter depending upon the size of the condenser and the length of the lines.

It looks like the liquid line in your photo is 3/8", which would make it okay.

I did a quick Google and found this generic diagram that sort of explains what I'm talking about.

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Bain, I'm not questioning - I'm asking: Do you think the line to the left of the drier is 3/8"? It looks TINY to me.

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A P.S. to the above. I just looked at the destructions for my own unit. The liquid line is supposed to be 3/8" for all applications UNLESS the condenser is 1 1/2 or 2 tons. THEN the suction line is supposed to be 5/8" and the liquid line is supposed to be 1/4".

That's why I said you need to check the manufacturer's specs.

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I was typing while you were posting. The line in your photo may be 1/4", which would be okay under the right circumstances.

And you can question me any time you want. I'm not THAT big of a prick, am I?

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I was typing while you were posting. The line in your photo may be 1/4", which would be okay under the right circumstances.

And you can question me any time you want. I'm not THAT big of a prick, am I?

What you talkin' 'bout, Willis? You're one of the classic hot sauces in the TIJ recipe. [:-thumbu] [^] [:-hspin]

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Hello Mike,

I look for 3/8 liquid refrigerant lines on any residential split system above 1 1/2 tons. For the vapor line, I look for 3/4 copper on systems up to 3 tons, and 7/8 on units from 3 1/2 tons on up.

You won't find this info in any book. It varies by manufacturer. These are simply common figures based on my own experience. Others will likely volunteer differant values.

The consequences of undersized liquid lines is loss of subcooling at the inlet to the constriction device (expansion valve, piston or capillary tubes). By subcooling, I mean the difference between the pressure at which the liquid refrigerant begins to evaporate and the actual pressure at the inlet to the constriction device. When this difference is reduced to zero, evaporation begins within the liquid line and cooling capacity begins dropping off. This problem begins sooner if the evaporator is situated at a higher elevation such as the second story attic with the condenser on the ground outside. Reduced liquid line size will promote premature evaporation of liquid refrigerant. This is what I mention when I write up undersized liquid lines.

Thread drift: This is the first post I've typed without looking at the keyboard. Been taking an online course.

Marc

EDIT: Replaced 'superheat' with 'subcooling'.

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.

Thread drift: This is the first post I've typed without looking at the keyboard. Been taking an online course.

Marc

Good for you, Marc! You will never ever regret learning to type. It's a definite time and money saver. Not to mention, it's nice to get to the point that thoughts can just flow onto the screen. Yes!... [:-thumbu] I've been typing since college - 38 years ago - and I am probably up to about 50 words a minute, which certainly isn't blistering, but it really makes life easier.

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Hello Mike,

I look for 3/8 liquid refrigerant lines on any residential split system above 1 1/2 tons. For the vapor line, I look for 5/8 copper on systems up to 3 tons, and 3/4 on units from 3 1/2 tons on up.

You won't find this info in any book. It varies by manufacturer. These are simply common figures based on my own experience. Others will likely volunteer differant values.

The consequences of undersized liquid lines is loss of superheat at the constriction device (expansion valve, piston or capillary tubes). By superheat, I mean the difference between the pressure at which the liquid refrigerant begins to evaporate and the actual pressure at the inlet to the constriction device. When this difference is reduced to zero, evaporation begins within the liquid line and cooling capacity begins dropping off. This problem begins sooner if the evaporator is situated at a higher elevation such as the second story attic with the condenser on the ground outside.

Thread drift: This is the first post I've typed without looking at the keyboard. Been taking an online course.

Marc

Vapor line, constriction device - where on earth did you come up with these terms?

Superheat has NOTHING to do with the liquid line. Basic refrigeration 101 - liquid begins to boil off mid-way in the evaporator - the temperature above the corresponding temperature/pressure IN THE SUCTION LINE is superheat. Honest to God I've never read more gibberish in my life.

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You're right on the superheat thing, the correct term is subcooling. Memory doesn't always serve me well.

'Constriction device', liquid line and vapor line are common terms where I'm from.

Marc

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You're right on the superheat thing, the correct term is subcooling. Memory doesn't always serve me well.

'Constriction device', liquid line and vapor line are common terms where I'm from.

Marc

I've never heard the term "constriction device," either. I wanted to learn, so I Googled it, and was surprised to see that only one kind of device was mentioned on the first results page. Are you certain you aren't confusing your professional life with your personal life, Marc?

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By golly, ED came up on top when I googled 'constriction device' too. No John, no confusion. Try 'refrigerant constriction device'.

Marc

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By golly, ED came up on top when I googled 'constriction device' too. No John, no confusion. Try 'refrigerant constriction device'.

Marc

I was teasing you. It was a dumb joke . . .

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Constriction device', liquid line and vapor line are common terms where I'm from.

Marc

A pound is a pound the world around. Suction line, liquid line, expansion valve/capillary tube and hot gas line.

It's this statement Marc that makes zero sense:

By superheat, I mean the difference between the pressure at which the liquid refrigerant begins to evaporate and the actual pressure at the inlet to the constriction device. When this difference is reduced to zero, evaporation begins within the liquid line and cooling capacity begins dropping off. This problem begins sooner if the evaporator is situated at a higher elevation such as the second story attic with the condenser on the ground outside.

????

I'm not even sure where to start.... I'm trying to make heads or tails out of the statement but it's difficult to say the least.

Sub-cooling is the temperature below the corresponding pressure/temperature relationship for the given refrigerant.

When this difference is reduced to zero, evaporation begins within the liquid line and cooling capacity begins dropping off.

Are you saying that when the sub-cooling is reduced to zero?

Then yes, that would be an undercharged condition. But not something that could be traced back to an undersized liquid line. The liquid refrigerant wouldn't immediately boil right after the expansion (constriction) device. If the refrigerant boiled right after the whatever device then there would be frost at the outlet and the superheat would be way high.

Back to the original question though, can you even purchase a line set that is less than 3/8 on the liquid line? I don't think so. Do most HVAC technicians roll their own in the field with regards to the line set - no, I think not.

Anyway.... awkward pause.... how about those Steelers?

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Constriction device', liquid line and vapor line are common terms where I'm from.

Marc

A pound is a pound the world around. Suction line, liquid line, expansion valve/capillary tube and hot gas line.

It's this statement Marc that makes zero sense:

By superheat, I mean the difference between the pressure at which the liquid refrigerant begins to evaporate and the actual pressure at the inlet to the constriction device. When this difference is reduced to zero, evaporation begins within the liquid line and cooling capacity begins dropping off. This problem begins sooner if the evaporator is situated at a higher elevation such as the second story attic with the condenser on the ground outside.

????

I'm not even sure where to start.... I'm trying to make heads or tails out of the statement but it's difficult to say the least.

Sub-cooling is the temperature below the corresponding pressure/temperature relationship for the given refrigerant.

When this difference is reduced to zero, evaporation begins within the liquid line and cooling capacity begins dropping off.

Are you saying that when the sub-cooling is reduced to zero?

Then yes, that would be an undercharged condition. But not something that could be traced back to an undersized liquid line. The liquid refrigerant wouldn't immediately boil right after the expansion (constriction) device. If the refrigerant boiled right after the whatever device then there would be frost at the outlet and the superheat would be way high.

Back to the original question though, can you even purchase a line set that is less than 3/8 on the liquid line? I don't think so. Do most HVAC technicians roll their own in the field with regards to the line set - no, I think not.

Anyway.... awkward pause.... how about those Steelers?

Well, purely for my sake, the one thing you haven't done is clue me in on if there's anything at all to say about the situation.

I'm beginning to conclude, based upon recollections of the previous thread and this one, that the answer is most likely: no need to go there.

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Constriction device', liquid line and vapor line are common terms where I'm from.

Marc

A pound is a pound the world around. Suction line, liquid line, expansion valve/capillary tube and hot gas line.

It's this statement Marc that makes zero sense:

By superheat, I mean the difference between the pressure at which the liquid refrigerant begins to evaporate and the actual pressure at the inlet to the constriction device. When this difference is reduced to zero, evaporation begins within the liquid line and cooling capacity begins dropping off. This problem begins sooner if the evaporator is situated at a higher elevation such as the second story attic with the condenser on the ground outside.

????

I'm not even sure where to start.... I'm trying to make heads or tails out of the statement but it's difficult to say the least.

Sub-cooling is the temperature below the corresponding pressure/temperature relationship for the given refrigerant.

When this difference is reduced to zero, evaporation begins within the liquid line and cooling capacity begins dropping off.

Are you saying that when the sub-cooling is reduced to zero?

Then yes, that would be an undercharged condition. But not something that could be traced back to an undersized liquid line. The liquid refrigerant wouldn't immediately boil right after the expansion (constriction) device. If the refrigerant boiled right after the whatever device then there would be frost at the outlet and the superheat would be way high.

Back to the original question though, can you even purchase a line set that is less than 3/8 on the liquid line? I don't think so. Do most HVAC technicians roll their own in the field with regards to the line set - no, I think not.

Anyway.... awkward pause.... how about those Steelers?

Well, purely for my sake, the one thing you haven't done is clue me in on if there's anything at all to say about the situation.

I'm beginning to conclude, based upon recollections of the previous thread and this one, that the answer is most likely: no need to go there.

Mike, first photo in your OP: that's 1/4 going into the house. 3/8 coming from the outside unit. You did notice the bi-directional arrow on the filter dryer, did you? A bidirectional is needed for a heat pump, so this system might well be one.

Terry, You'll pardon me if I ignore your posts for a while. I figure that's the best way to respond to your replies above.

Marc

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Respond, don't respond, whatever.

When I do is respond to a post I believe that what I'm adding to a post is accurate or just for a bit of humor to try and keep it light. If someone posts a response in a HVAC thread, that has accurately answered the question, then I see no need to interject. You, on the other hand, respond as if it is important to maintain quantity, even if it is just to affirm what the responder had to say, as if it is important to put your name out there. It's interesting behavior.

I have no axe to grind with you Marc, I really don't. However I will stand toe to toe with anyone that starts to pontificate and expound as a self proclaimed expert and what they're putting, into type, makes little, or no sense or is inaccurate.

I don't know a lot about many things but I do know HVAC. When someone posts nonsense I call it out. We are here to provide accurate information because others depend upon it.

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OK, I'm sitting down to write up this morning's inspection.

we've been down this road some before, but it's come up again, and it's high time for me to actually hammer out a good boilerplate comment about this condition:

If we think back to our basic geometry days, we'll recall that a small change in diameter results in a huge change in volume. It's that truth that always has me worried when I see a new condensing unit hooked up to a line set that doesn't match in diameter to the unit. I don't know if they just re-used the original line set or just threw in what they had on the truck, but the wet line is easily 50% smaller than the line coming out of the condensing unit.

I'm just getting around to addressing this post Mike - I'm sorry for the slight detour.

Please do not use the term "wet line". Air Conditioning components have distinct names and terms. When we stick to these terms we are all on common ground. The suction line is always a "wet line" under the right conditions. A liquid line, under the wrong conditions, could also be a "wet line".

Please, let us all agree to use industry standard names.

Get a Carrier or Trane refrigeration manual Mike and commit it to memory.

It's pretty easy to relate certain AC tonnage to piping size once you know the basics. If you feel that something looks fishy then it most likely is.

For Boilerplate.

The home is X square feet. This dictates an X amount air conditioning unit. This air conditioning unit needs X diameter piping to operate properly. I believe that the refrigeration piping is improper, x liquid line, x suction line and x hot gas line. Call a licensed/qualified HVAC company to verify and repair as needed.

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OK, I'm sitting down to write up this morning's inspection.

we've been down this road some before, but it's come up again, and it's high time for me to actually hammer out a good boilerplate comment about this condition:

If we think back to our basic geometry days, we'll recall that a small change in diameter results in a huge change in volume. It's that truth that always has me worried when I see a new condensing unit hooked up to a line set that doesn't match in diameter to the unit. I don't know if they just re-used the original line set or just threw in what they had on the truck, but the wet line is easily 50% smaller than the line coming out of the condensing unit.

I'm just getting around to addressing this post Mike - I'm sorry for the slight detour.

Please do not use the term "wet line". Air Conditioning components have distinct names and terms. When we stick to these terms we are all on common ground. The suction line is always a "wet line" under the right conditions. A liquid line, under the wrong conditions, could also be a "wet line".

Please, let us all agree to use industry standard names.

Get a Carrier or Trane refrigeration manual Mike and commit it to memory.

It's pretty easy to relate certain AC tonnage to piping size once you know the basics. If you feel that something looks fishy then it most likely is.

For Boilerplate.

The home is X square feet. This dictates an X amount air conditioning unit. This air conditioning unit needs X diameter piping to operate properly. I believe that the refrigeration piping is improper, x liquid line, x suction line and x hot gas line. Call a licensed/qualified HVAC company to verify and repair as needed.

Aye, aye, captain. Thanks for the heads up.

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Originally posted by Marc

By golly, ED came up on top when I googled 'constriction device' too. No John, no confusion. Try 'refrigerant constriction device'.

Marc

[/quote Piston/orifice/txv,lots of differant terms for same part.

Lennox used loops in the 1/4" liquid line just before the coil as a metering device on many older units

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