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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,
The copper refrigerant lines move the refrigerant between the condenser and the evaporator. Refrigerant lines are normally arranged in pairs, with the larger diameter line carrying gas and the smaller one carrying liquid. The larger refrigerant pipe containing cool gas is typically insulated to prevent condensation and increase efficiency.
The most common problems with refrigerant lines are mechanical damage, leakage and corrosion. Refrigerant lines are frequently damaged where they pass through the house wall. Leaking refrigerant lines are usually identified by oil deposits on the line.
Illustration, above left, courtesy of Carson Dunlop Associates. [Click enlarge any image]
I had a refrigerant return pipe blow a small hole (about 18 months after install). It turned out the copper pipe as touching the aluminium cover that had been attached on top of the pipe run in this one place. I could see copper had deposited itself on the aluminium inside the cover which looks due to possible galvanic corrosion over time - but the blow out was a pin hole which, it is surmised, was due to electrical current running down from a lightening strike.
It seems clear to me the copper pipe should not have been touching the cover, it only did so in this one place. It must have been protruding some obvious distance to touch the cover when this was installed. Would I be correct that this was an install error?
Thanks for this note, Jon. Indeed there could be a galvanic corrosion problem when aluminum is touching copper; such leaks also occur not just from a lightning strike but also from improper electrical grounding of the equipment and sometimes from vibration rubbing the two components together.
Use the page top or bottom CONTACT link to send me some whole unit and then closeup photos of the situation and we can comment further.
2016/08/25 Anon wrote [by email to editor]
Thanks for your posted response regarding the install I have where they left the copper refrigerant return pipe touching the inside of the aluminum protective cover at one place.
The pipe blew out at this point. The guess is electrical current caused this. As I suspected, the pipe should have been clear of the cover as there is risk of galvanic corrosion and friction damage. Now if appears the touching is the reason for an electrical arc?
There was no sign of scorching on outside of cover - only the black streaks showing in picture on pipe. I never saw the pipe, only the cover, and this picture has just been provided by engineers.
You mention possible electrical grounding issue as a reason? There is no sign anywhere on house of an electrical strike - i am no expert but might expect to see some scorching somewhere.
So if an electrical arc the current must have run down copper pipe and arced where the two metals made contact. There was a copper deposit on inside of the cover where they had touched.
Your opinion on what logically appears to be an install fault due to touching pipe and cover is very appreciated. If this could also denote a grounding issue that info is also appreciated.
The pitting and crater and black marks look a lot like an electrical arc, not a vibration wear-through.
Also see REFRIGERANT LEAK REPAIR
Yes electrical arc does seem most likely. I do believe the proximity of the pipe touching the casing allowed the arcing to happen at this point - and there should not have been a point where the two touched - I believe am correct in saying this?
Where the electrical current came from is unexplained. Lightening is offered as an explanation but no sign of any strike anywhere. E,g The casing was clean all the way up - no scorching. Should I be looking for a possible electrical fault connected to the AC equipment.
Yes certainly. I'd start by a visual inspection of the equipment for a loose wire, connection, or component, and also I'd look for burn marks or overheating signs inside the equipment. From your photos I lack a more distant perspective view (send that along if you can) that might be informative.
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 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,
Refrigerant lines need to be securely installed to minimize vibration that causes noise and damages piping. Reciprocating compressors, in particular, cause vibration. Steel braided flexible refrigerant lines (a must for spring isolated reciprocating compressors) minimize this vibration. ...
Refrigerant lines that rub against solid objects wear holes through copper and create a leak. For this reason, when refrigerant lines pass through walls, the line should pass through sleeved openings in such a manner that the lines do not touch. There are several commercially available pipe clamping systems that allow pipes to be held rigid without causing damage to them. Most include some form of rubber grommet around the pipe, which is then secured within a bracket. Many building codes specify minimum support spacing.
Piping should also be protected from mechanical damage. Where piping is exposed to possible damage, the lines should be routed out of the way or be protected in some form of chase.
Burying refrigerant lines should be avoided.
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 piping should be insulated. 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.
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.
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.
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.
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.
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.
Unused refrigerant piping or tubing should be stored with its ends capped to keep dirt and moisture out of the piping.
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.
This article describes three different temperature ranges for soldering copper piping or tubing along with some general copper pipe or tubing soldering advice.
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.
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.
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,
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
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Where can I find the plastic covers for my heat pump lines that run on an exposed wall.
Your local HVAC supplier carries piping covers and insulation. You may also find these products at building suppliers such as Loews or Home Depot.
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