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Question DetailsAsked on 8/16/2017

A/C Unit copper and aluminium joint pipe leaking? is there a fix for that , instead of replacing the entire coil?

My A/C unit is not producing cool air and we end up filling the refrigerant every year for the past 2 years and later I found we don't need to fill the refrigerant every time and need to find a leak.
Now we found the leak by HVAC technician. They are saying it cannot be repaired and we need to replace entire coil.
one company quoted with about $1800USD without the parts(Evaporated Coil) cost. As part of the coil replacement they are planning to do Air duct ceiling test. I am not sure that is require or not? any advice on this is appreciated.

thanks in advance.

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1 Answer


$1800 without the coil is really at high end of this type of repair, assuming ordinary accessibility - normally $1500 -2000 range WITH the coil cost included, or $1000-1500 if coil is being provided free by manufacturer under warranty. So I would get another couple of quotes from well-rated Heating and A/C contractors (your Search the List category).

The air duct sealing test (actually duct leakage test) is around $100-200 in most areas - and is probably something they are offering to you in the "package deal" as a lead-in to selling you dut sealing - which is cleaning the ducts, then spraying in a sealant which seals most of the duct leaks. In some houses this can be very beneficial (especially if ducts run in outside walls or outdoor exposed crawlspace or basement where duct leakage = "conditioned" air leakage outside of the "conditioned space"= energy wastage), in others it may help with temperature balance between parts of the house but does not save you money because in ducts located within the "conditoned space" (interior walls, heated basement ceiling, etc) the leakage, while maybe appearing where it is not most wanted, is not actually eswcaping the conditioned space so is not "wasted" energy - just misplaced but still heats or cools the house overall (unless it is so severe in one area like a garage that the leakage area is excessively heated or cooled).

Depending on how extreme your annual heating / cooling bills are, whether your unit has trouble keeping up with the demand, and especially if your ducts are outside the building envelope (so leakage = wasted energy) you might have them do the test to determine how bad your ducts are - or you might ask for a requote without it. Commonly, metal ducts (assuming not rusted through or disconnected somewhere) tend to run 10-25% wastage and about 15% is considered the point where sealing might save you money - flex ducts are tighter overall but the joints are the pits - both in terms of leakage and coming apart, so your leakage can run 50% or more in that case - though generally flex ducting is not as much helped by air sealing because the leakage points at the joints are commonly too dramatic to be sealed by the air sealing method, so if losses are high generally you really need a duct camera run also to see if and where you have separated joints or seams.

As for the coil leak - while it is possible to braze aluminum/copper coils, generally very few contractors will do it (or even have the right cleaning, flux, and brazing materials to do it, and probably none will warranty it for more than a day to a week at most, because while it might be a loose press-fit connection, more likely it is leaking because of corrosion between the incompatible metals. This is a MAJOR cause of reduction of coil life from the historic 15-25 years down to 10-15 years today and in many instances 5 years or less (I have seen as little as 6 month life with some imported coils), as manufacturers race to the bottom in quality to be cost competitive. Generally, such a leak, if not just where the A/C system refrigerant tubing come into or out of the coil unit, is due to corrosion and is not going to braze up well - especially because it is not possible to get the oil (carried in the refrigerant) out of the joint without disassembling it, which would generally mean taking the entire coil apart - definitely not an option.

Some contractors will do a "blob repair" on a coil leak with no promises on how long it will last (sometimes long time, sometimes not at all) - done by building up a "blob" of brazing metal on and around the joint, basically as a molten metal bandaid over the leak and the adjacent metal, hopefully covering over the likely area of corroded metal. This assumes they can even get at it without taking the coil out of the duct - if it has to be taken out to repair it, you are into most of the cost so might as well spend the $300 to maybe $500 for a new coil which hopefully has a 10 year warranty (on parts only) versus a couple hundred $ for a "who knows how long it will last" brazing repair. Probably almost all vendors (except maybe a few "old-school" repairmen who know how to "fix" HVAC systems rather than just swap out parts like the current training emphasizes) will recommend or indeed only to replacement - not a repair.

Personally, given that the coil is mixed aluminum and copper rather than all copper life the old ones, if the coil were over say 10-15 years old I would not try to repair it if it were mine, unless the leak point was really accessible without removing the coil. At that age, with mixed metals, it is awfully likely that if this is a corrosion hole-through (as opposed to a fitting leak), that the rest of the coil is going to start showing corrosion holes pretty soon anyway, so in that case replacing the coil (or the entire system) would probably be the smartest move.

If the problem is where the copper tubing goes into an aluminum header piece on the coil, sometimes there is enough brass or copper stickout to brazeon a new fitting there, sometimes it is a threaded fitting which can be removed and replaced, and there are also mechanical flare-type repair kits from Trane and others for that - to essentially put a new mechnically-fastened (with sealer material as it is installed) connection to the coil for the copper tubing to be brazed to.

One other thing - if looking at $2000 range for the repair, is the repair/replace issue - aggravated by the R-22 (Freon) phase-out issue if yours is an older, Freon refrigerant unit. you can find lots of previous questions about the repair/replace issue and thoughts on the economics of going to newer units, potential energy savings with the newer EPA-mandated higher efficiency base units or with even higher efficiency units, can be found in the Home > HVAC link under Browse Projects, at lower left.

Answered 1 year ago by LCD

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