Refrigeration equipment piping for air conditioners & heat pumps: this air conditioning repair article discusses the refrigeration piping requirements, insulation, mechanical fastening, and allowable distances as well as errors in air conditioning refrigerant piping installations that risk future refrigerant leaks or malfunction in the cooling equipment.
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According to Carson Dunlop Associates Home Reference Book,
Absence of slack in the air conditioning system coolant lines at the compressor units can cause leaks: should the compressor move, perhaps because its supporting pads settle, there will be likely leaks at these lines. You should review this question with your HVAC service person. This item may be deferred until next maintenance or service.
Our refrigerant line photo (below left) shows worn insulation and a crimped condensate drain line. Our photo of a pair of outside compressor units (below right) shows what looks like a neat installation, but the mounting of the refrigerant piping against the building wall and absence of slack is just asking for a refrigerant leak in these systems.
Carson Dunlop Associates' sketch (left) illustrates the installation of the refrigerant suction and liquid lines and points out that the refrigerant lines should slope downwards towards the condensing unit - a detail that helps direct refrigerant oil back towards that component.
Also notice that the extra length of refrigerant piping that may be found both indoors at the air handler and outdoors at the condenser / compressor unit should be coiled and positioned properly as well.
According to McQuay International, a large producer of refrigeration equipment,
Use Nail and Screw Plates to Protect Refrigerant Tubing
Where refrigerant piping (or condensate drains) are routed through building walls, floors, or ceilings, if the holes drilled through framing members place the tubing too close to an interior or exterior wall surface, there is a risk that a drywall nail or screw, or an exterior siding nail will puncture the refrigerant lines.
We protect against this hazard by nailing standard nail plates across the face of each stud, joist, or rafter where this risk is present.
Our refrigerant line photo (left) shows liberal use of these nail plates on the interior face of wall studs where the routing of refrigerant lines was close to the interior wall surface.
Because the builder had not yet completed the exterior siding (just the OSB sheathing was in place), we also had to watch out for use of long siding nails that might puncture one of these lines.
Outside the building in areas where this was a concern, because the sheathing was already in place, we simply marked "no-nail" areas on the OSB.
Refrigerant Line Insulation Requirements & Proper Installation Details
Manufacturers also recommend wrapping the insulated refrigerant lines exposed to outdoor weather, using an appropriate weatherproof tape.
For details about proper installation of insulation on HVACR refrigerant lines or piping please see REFRIGERANT PIPING INSULATION.
Crimped Refrigerant Line or Tubing Insulation
Air conditioner manufacturers include installation instructions with each unit. It's worth taking the time to read all of those details as the manufacturer has the same desire for a successful and trouble-free installation as the home or business owner or the HVAC installer.
Among these instruction details you'll read how the manufacturer wants the refrigeration lines installed, including the following:
When installing insulation over the refrigerant tubing, do not over-tighten the foam insulation (typically held in place with plastic ties or tape). Crimping the insulation along its refrigerant tubing pathway creates points of less and possibly inadequate insulation.
Missing or inadequate refrigerant piping insulation means a system that operates at a lower efficiency and it risks condensate drips into problem areas such as wall or ceiling cavities - a mold risk.
Air Conditioner Refrigerant Line Diameters & Lengths vs. Distance Between Compressor/Condenser and Air Handler/Evaporator Coil
How Far Apart Can I Separate the Air Conditioner Compressor/Condenser from the Air Handler/Evaporator Unit?
I live in a townhouse and have a split air conditioner system. The compressor is currently on the roof, but it may need to be relocated to ground level. The other unit is in the attic. How far away from the house can the compressor be (maximum, not minimum). I do not want to put the unit on my terrace, which is next to the house, because it would diminish our ability to use the terrace due to noise, etc. Could the unit be located approximately 37 feet away from the house without affecting it's function? This would place it at the back of the garden, either behind a fence or obscured by a shrub. - Anon.
Answer: Almost any A/C equipment separation distance can be made to work, but the installer will need to take a look at refrigerant piping diameter guides
Moving an air conditioner compressor to a distance of about 40 feet from a building wont' prevent it from working, but the installer might need to adjust the diameter of the refrigerant lines to be sure that the equipment is working at 100% of its capacity.
A more careful answer to your question is not so much that there is a specific distance limit between the A/C compressor and A/C evaporator coil so much as a need to get the size (diameter) of refrigerant lines and amount of refrigerant charge correct - that is, if we exceed some distance, probably like 100', we may need to increase the refrigerant piping diameter as well as the refrigerant charge for the system to work properly.
There is a more subtle technical concern with refrigerant velocity in the line. If the velocity is too low, refrigerant oil may not be properly distributed in the system. In addition to total length of refrigerant piping, the number of elbows, bends, fittings, also affect flow and have to be taken into account.
Each A/C manufacturer offers their installer technicians equipment installation instructions that include how to size refrigerant piping properly. The instructions may include complex calculations, or simply a chart of separation distances between the outside compressor/condenser unit and the inside air handler/evaporator unit.
If there is not a "table" of distances and pipe diameters for a specific air conditioning system, then the manufacturer will expect the installer whose layout is different from the usual distances to make some measurements on the system and to adjust it accordingly.
Diameter of Refrigerant Piping & Tubing
In a nutshell, the size in diameter of the refrigerant suction and supply piping needs to be determined by the installer based on the distances involved, the equipment tonnage, changes in elevation between compressor and evaporator coil, the number and type of fittings in the refrigerant piping system, ambient operating temperature ranges, and other cooling equipment specifications given by the manufacturer.
If the installer places the equipment far enough apart that s/he should have used a larger (or smaller) diameter piping system, the A/C system will still work, but its cooling capacity may be reduced.
A cooling line that is too big in diameter OR too small in diameter can cause the equipment not to work properly or efficiently.
Copper Tubing ID versus OD: internal diameter versus outside diameter
It's easy to get confused about pipe sizes or diameters when discussing flexible copper tubing. Refrigeration technicians often refer to flexible copper refrigerant tubing by its outside diameter or "OD" while plumbers usually refer to any piping by its inside diameter or "ID".
A 1/4" OD (outside diameter) flexible copper refrigerant line actually has about a 1/8" ID (inside diameter). So when you are measuring or ordering piping, make sure you and your supplier are talking about the same size by using "OD" or "ID" in your measurements.
Storage of Refrigerant Piping or Tubing
Unused refrigerant piping or tubing should be stored with its ends capped to keep dirt and moisture out of the piping.
Refrigerant Piping or Tubing Connections
Most HVAC systems that we have inspected and all that we have installed or repaired used soldered or brazed connections for copper refrigerant piping on both suction and high pressure lines.
Some manufacturers, codes, and procedures also allow flare fittings - something we have used on some LP gas lines but in our opinion flare fittings are more leak prone than soldered connections. (We do not use compression fittings on refrigeration and air conditioning systems.)
In the opinion of some HVAC instructors, half of the leaks found in refrigerant piping are traced to defective soldered or flared connections so it's important to make these connections as close to perfect as you can during system installation or repair. 
Sections of flexible copper tubing to be soldered or brazed together are connected using a procedure called swaging.
A swaging tool (see our sketch above and our photograph at left) is used to join similar-sized sections of refrigerant piping without requiring an additional coupling fixture. Swaging tools come in a range of sizes - two of mine [DF] are shown at left.
Typical swaging tools used for refrigerant piping connections handle tubing sizes 3/16", 1/4", 5/16", 3/8", 1/2" and 5/8" O.D. (Refrigerant tubing sizes are specified in O.D. or outer diameter).
The advantage of this approach is that we eliminate at least one soldered joint, increasing the reliability of the refrigerant piping system (or other piping) against leaks.
The swaging tool is inserted into the end of the copper tubing through a flare block or, if the installer is experienced, the tubing may be hand-held.
The swaging tool is carefully hammered until it has expanded the copper tubing internal diameter (ID) sufficiently to permit it to slip over the connecting copper tubing section.
The interior of the enlarged end of tubing and the exterior of the factory-sized tubing that will insert into the enlarged mate are both cleaned, primed, or fluxed and soldered according to the manufacturer's instructions, typically using silver solder, or in some applications, brazing.
Guide to Soldering Materials & Temperatures for Refrigerant Piping & Tubing
This article describes three different temperature ranges for soldering copper piping or tubing along with some general copper pipe or tubing soldering advice.
General Soldering Advice for Copper Piping or Tubing
Temperature Ranges of Copper Soldering
The copper tubing ends to be connected are cleaned, sanded, treated with soldering or brazing flux, and soldered or brazed.
When a capillary tube is to be soldered take are not to place soldering flux too far into the joint or the solder may flow over and close the end of the capillary tube. (see our sketch).
Watch out: in our OPINION (and that of other HVAC technicians) compression fittings should never be used and in best practice flare fittings should also not be used on refrigerant gas or liquid piping. Soldered connections are much less likely to leak under the harsh conditions to which refrigerant piping is subjected: vibration, high pressures, high temperature swings, and outdoors, weather exposure.
Refrigerant Piping Sizing and Run Length: refrigerant pressure drop and temperature loss
For example, measuring the refrigerant gas line pressure drop (or temperature change) on the suction line (return to the compressor) will show (typically) that a 4 degree temperature loss through the refrigerant line will result in an 8 percent loss in cooling capacity of the system.
Or on the discharge line (output from the compressor) will show (typically) that a 4 degree temperature loss through the refrigerant line will result in a 2 percent percent loss in cooling capacity of the system.
So it's not that the air conditioner won't work at all if the compressor/condenser is located at an unusual distance from the air handler/evaporator coil, it's more that it may lose some capacity and have to work harder - meaning higher electrical bills and in extreme cases, shorter equipment life.
Equivalent Refrigeration Piping Length to Include Fittings, Controls Devices
ASHRAE and some air conditioner manufacturers such as McQuay provide a refrigeration piping guide that gives complete, detailed guidance and charts on refrigerant line sizing (diameter) as a function of length of run. The company points out that the entire liquid refrigerant line is composed of more than just piping, and includes
Each of these devices or components contributes volume to the refrigerant piping system and must be considered in designing the "equivalent length" of the entire refrigerant piping system in order to determine the proper refrigerant charge. For example,
Technical Note on Refrigerant Piping: HVAC economizer detail using refrigerant line brazing or soldering together of the Low Pressure & High Pressure lines for deliberate heat exchange
In some refrigeration system designs, a low-temperature (heat laden) vapor line (suction line) is soldered alongside the high-temperature, high-pressure liquid refrigerant line. This conjoining of the two refrigerant lines is likely to be done where the vapor line is entering the compressor/condenser unit.
The purpose of this line-to-line soldering is to act as a heat exchanger, to reduce the temperature of the liquid refrigerant that is going to enter the metering device (TEV or cap tube), gaining some benefit to system operation - we want a lower refrigerant temperature at the point where the liquid refrigerant is about to be metered or released into the cooling coil (evaporator coil in the air handler).
A second benefit of this heat exchange is that in the larger suction line entering the compressor, the refrigerant enters at a higher temperature, easing the compressor's job of compressing and raising the refrigerant temperature on the condenser side, so that the refrigerant is (by being hotter) better able to transfer heat to ambient air in the environment around the condensing coil.
Other forms of air conditioner and heat pump economizers and economizer tricks of the trade are discussed at AIR CONDITIONING HEAT PUMP SAVINGS
Continue reading at REFRIGERANT PIPING INSULATION or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: can I use standard 3/4" diameter copper piping instead of flexible 3/4" copper tubing for the refrigerant suction line?
I have no problem bending the smaller 3/8 tubing. However, I am having a difficult time installing the ¾ line without crimping the pipe.
My question is can I use standard ¾ inch cooper piping instead of the ¾ in tubing? I’m good at plumbing.
I could then neatly run the pipe to within a foot of the condenser and coil and have the technician complete the install. Thanks for your help and the great website. Steve
Reply: Yes but ...
Certainly I've seen [DJF] commercial HVAC installations where larger diameter soldered-joint copper piping was used for refrigeration liquid or gas movement - there is no conceptual problem with that approach but
Bending copper tubing - tips for
Incidentally, among my plumbing tools I keep a set of tightly coiled springs of appropriate inner-diameter to slip over flexible copper tubing that needs to be bent without crimping or kinking. These springs, sold at HVAC suppliers, slip over the tubing in the area where you want to make the bend, and the steel of the spring holds the copper tubing keeping it round so that you can make a bend without any crimps.
Also you may have noticed that even smaller diameter flexible copper tubing can become increasingly difficult to bend and re-bend in the same area of tubing. That's because as you bend the tubing the heat of the bending process alone is sufficient to anneal the copper, making it harder. So we try to get the bends nice and neat and right the first time.
Need to know what kind of fitting is used on a Carrier Air conditioner that attaches freon line to condensing unit - VInce
Vince the two common piping attachment on refrigeration lines are soldered/brazed copper tubing at which a female connecting end is prepared using a swaging tool, and in some communities, carefully-prepared flare fittings. Details are in the article above.
Question: Are exposed copper refrigerant lines ok outdoors?
Is it safe to have all copper refrigerant lines installed on the outside of the house? Thank you, Caren
Reply: Yes but refrigerant piping should ben insulated, supported, and where outside, wrapped
A competent onsite inspection by an expert usually finds additional clues that help understand whether or not there are problems with your air conditioning system or its installation details. If you see signs of amateur workmanship on one part of the system it's appropriate to raise a question about other installation details that may not have been noticed, and thus to take a closer look.
That said, it is perfectly normal for copper air conditioner or heat pump piping to continue outside the house in order to connect to and from the compressor/condenser unit.
However air conditioner manufacturers and other expert sources include installation instructions that specify that the refrigerant lines should be insulated, supported, and wrapped with a weatherproof protective tape. Also be sure that the opening in the building wall where the refrigerant lines emerge has been properly sealed against leaks and insect pests.
Question: why are the refrigerant lines vibrating noisly - it sounds like a freight train!
(July 5, 2011) Maura said:
What would cause the refrigerant lines to vibrate so loudly it sounded like a freight train? What is considered normal vibration of the gas line? Because now causes copper line to vibrate very loudly. The new unit was installed last year, but problem just started. Thank you for any advice you can offer
Don't "solve" the problem by just isolating the piping from the building with foam - that's treating the symptombut not an underlying problem.
I'd start by looking for the source of vibration - it's more likely to be a compressor that is not mounted properly, has some loose component, or if originating indoors, a loose fan motor mount or blower assembly. Let us know what you find as it may help other readers.
Thank you Dan I will try to explain exactly what happened. Had a power outage about 2 weeks ago, when the power came back on an extremly loud noise was coming from basement. It was the lines coming from ac unit. Noise was very loud! Turned circuit breaker off than back on it stopped. Unit was also working. Called ac guys said it was a power surge, I don't know.
Then a few days later the lines started to make a similar noise but not as loud turning power off did not stop it. Realized copper pipe was vibrating up against insulated pipe. Called ac guys again because noise would not stop all they did was tape the copper wiring to stop the vibrating not really addressing why it is happening in first place. I asked if it might be a problem with compressor. Asked them check they put a hardstarter on which I know I don't need because that is not the problem. Then again last night air cycled on, the very very loud noise started again only lasted 10 seconds and stopped.
AC guys just left still telling me possible brown outs from electric co. I don't think so. Have you ever heard of anythin like this? Shoul I have them replace compressor it is still under warranty. Thank you very much any advice would be helpful.
We need to know if the vibration originates with the outside compressor/condenser or the indoor air handler unit. If it's outside in origin, and because replacing a compressor is costly, you'd sure want that done (if needed) under warranty. A power surge can damage a control board - in fact more likely than damaging the compressor itself. I'd ask for some more careful testing of the equipment that is buzzing.
Thank you Dan, it is definitely coming from the compressor/ condenser unit and much more than a buzzing noise. If you email your phone# I will call you and play back the recordings of the noise they are extremely loud!!! I am not sure if what ac guys are telling is accurate. Again thank you for your expertise, I greatly appreciate.
Having just arrived on an assignment out of the U.S., a phone playback is probably not practical, but certainly from what you have described, an accurate diagnosis of just what part(s) is (are) failing is in order; call the service co and ask them to send a senior technician. You might point out that the first tech, who taped the lines, appears not to have the experience to recognize that there is a problem.
You can also ask your electric company if they have been reducing voltage or if there have been brownouts in your area - explaining that you are diagnosing an electrical question, and making clear you aren't coming to them with a claim.
Question: I can't use copper refrigerant piping in my facility
(Apr 10, 2012) Joe said:
I am installing a 'mini-split' style 3 ton a/c unit. I absolutely can not use copper lines in my facility. It has been done previously using hoses and connectors. What is the max PSI on a typical split 3 ton units refridg. lines?
Joe: take a look at the specifications for operating pressure of the equipment you are installing. Typically you could be looking at a safe pressure rating of 200-400 psi. And the rating for hoses protected with metal braiding.
Question: what is the effect of short refrigerant piping
(Apr 24, 2012) MHND said:
what is the effect of short pipes between indoor & outdoor split AC unit
MHND maybe you need to send me a photo - I don't understand the question. The refrigerant charge on a system with long piping could require adjustment, and of course the pipes have to be supported and insulated, but they don't impact the system operation in either direction of length other than computing the proper charge quantity.
Now if you mean that a compressor/condenser was installed with no slack or loop to allow the piping to tolerate vibration, that's asking for a refrigerant leak.
Question: buried refrigerant lines
(June 6, 2012) Soo said:
We just bought a new home and discovered that the home inspector and the county inspector both missed the fact that the refigerant lines outside the house going to the compressor are buried underground. There is a concern now that we have a freon leak in that 30 foot section of pipe that is outside and under a foot of dirt. If the lines were insulated prior to being buried, is the concern of a leak valid?
The diagnosis of a refrigerant leak will center around the operation of your system and refrigerant charge measurement, not the refrigerant pipe routing. However depending on your climate and the insulating materials used, your piping insulation may not be effective.
Burying refrigerant lines was probably done to avoid damage that might occur to lines routed over ground for the distance you describe, though we don't understand why there was a need for 30 feet of separation distance. Happily the shallow depth means it's trivial to excavate and replace leaky piping, perhaps using a protected conduit for the replacement to make service in the future easier.
Question: ice on the refigerant line
(June 9, 2012) Cliff said:
I had a small block of ice around the the refrigerant line coming from ac unit outside after running it. What does this indicate?
Ice on a short exposed section of refrigerant line most often means that insulation is missing at that location. Persistent icing at the coil or other locations can indicate low charge and a refrigerant leak.
Question: ok to run the A/C for a long time?
(June 11, 2012) Zev said:
Can running a central A/C unit set for 66F for along periods of time damage the unit. I live in Washington, DC where it's frequently hot and humid.
Zev, running a central A/C for "long periods" - even several days at a time should not damage the unit, though it may damage your wallet when the electrical bill arrives. The equipment and its wiring and overcurrent protection, if properly installed, is designed to safely operate continuously for extended intervals.
Question: compressor is tripping the circuit breaker
(June 22, 2012) Bobby said:
I live in Denver and keep my a/c set around 65-67F degrees. Recently, with the hotter temps and moderately higher humidity, the compressor has been tripping the breaker, causing the unit to blow warm air. I just moved from New Orleans 6 months ago and am not familiar with differences in a/c performance/limitations between NO and Denver.
My landlord's a/c tech says that the higher altitude will cause the a/c system to be overworked if the thermostat is set below 72F. I have been unable to find any information to substantiate his assertion. Is there any truth to this?
Bobby if the circuit breaker is tripping the compressor motor or some other component is drawing abnormally high current - a sign of trouble. It's possible that a failing compressor motor doesn't show up until it's been working extra hard.
In sum Bobby, I have not come across your landlord's claim. more likely the compressor is failing and drawing overcurrent, or is hard starting.
(June 24, 2012) david said:
I have received quotes from different companies to replace my 20 year old 4 ton central a/c system. The existing system has 3/4 inch copper tubing for the refrigerant. I am looking at replacing the unit to a 4 ton Infinity or Performance series Carrier or a XR or XLi series Trane system.
One company said that it would be necessary to run a new 7/8" line. Another company said the existing line would be fine as the newer refrigerant flows easier. The esimated lentgh of the run between the air handler (inside the house) and the compressor (outside of house)is about 50'. What is the correct answer.
David, I don't know why the piping needs replacement unless it's damaged or leaky. A larger pipe just means a larger refrigerant charge, right? Please ask the first co why a new line is needed. The "flow easier" argument sounds nonsensical to me but probably that's because the fellow speaking with you was not an English major.
Perhaps what was meant was that to achieve adequate refrigerant flow rate in a high capacity system larger diameter piping is required.
Question: solder suction and high pressure refrigerant lines together?
(June 29, 2012) JohnSmith said:
My refrigerant lines go about 10' vertically down the outside wall of my house. They are right next to each other. If I solder them together would it increase the efficiency of my unit? It's a 3.5 ton R22 heat pump. Thanks.
In general I think the answer is yes. How about giving the manufacturer of your unit a call at their tech support number for confirmation that you're not creating any problem. I wouldn't do it, however. I'd worry about creating oxidized crud inside the piping - which then fouls the refrigerant metering equipment, as well as increasing line rigidity, perhaps increasing damage risk, and certainly making future refrigerant line replacement more costly.
Question: will the AC unit work with extra length of refrigerant line?
(July 28, 2012) Steve said:
If the tech left more coolant line than needed but still charged the unit for the amount of line he had will the unit still work as it is supposed to.
Steve I'm not sure "more coolant line than needed" is quite the case - good practice leaves some slack, even an extra coil, so that vibration and slight movement don't rip open a brazed refrigerant piping joint.
The refrigerant charge used by the HVAC tech normally includes an allowance for the total length (and diameter) of piping in the system. If the charge is too low you'll probably discover it as frosting at the cooling coil.
Question: re-use refrigerant lines
(Aug 19, 2012) Tom D said:
I have concealed 1/4 and 1/2 inch copper lines that feed my existing split case heat pump that recently died. Can I reuse these lines for a larger size heat pump system that says is needs 3/8 and 5/8 inch lines? My existing lines are embedded in the wall
Generally if the refrigerant piping is larger in diameter than needed that's not an issue except for having to calculate the refrigerant charge correctly. Lines that are too small may limit the system's operating capacity.
Question: cut and cap unused refrigerant lines
(Oct 2, 2012) John said:
I am demoing my ac unit. its old and i do not use it anymore. I wanted to know if i could just cut the copper lines and cap them in case i want a new on in the future.
I agree that soldering a cap in place on the refrigerant lines makes sense to keep them clean for possible future use.
(Nov 18, 2012) Dave said:
After meeting EPA requirements for demolition of a system, it is best to totally remove all system piping and not reuse it due to unkown conamminants which could damage a new system.
Thanks for the opinion Dave. But of course when a new system is installed, a filter/drier is installed as a matter of course. And previously used, clean copper tubing that was kept sealed ought to be as clean as copper tubing that was sitting somewhere in a warehouse.
I'd agree however that if older copper refrigerant piping was damaged, corroded, or had previously leaked I'd junk all of it rather than use suspect piping on a new installation.
(May 5, 2014) vm said:
I am told that a wire rubbed against the copper pipe on the out door unit. They said the vibrating caused the wire casing to wear off and cause the bare wire to puncture the copper pipe. Now the home warranty company is not covering it claiming that it is not "normal wear and tear". Is this correct? or are they just trying to get out of paying?
My opinion is of course the insurer wants to avoid paying on a claim. You need help from an attorney familiar with home warranty policies to review the terms of your policy. A wire rubbing that causes a refrigerant leak sounds like an installation error or a product defect.
Keep us posted.
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