I have some questions about the copper lines used in the air conditioning trade and how best to make connections if necessary (or if it's not a good idea to). I know this is kind of a different trade from regular plumbing but my question is strictly related to the condensate drain side and the copper.

So for background I noticed this ceiling water stain in one of the rental apartments. This is where the lines from the central AC air handler runs up into the attic and navigate inside the attic and eventually exit to the outside and runs down to the exterior compressor.





My first thought is it could be a roof leak just happened to be in that area, or it could be a leak in the lines that runs up there through the attic.

But it hasn't rain for two weeks so the chance of a roof leak is unlikely, plus I feel some beads of water, very slowly running down the group of tubing that exits the ceiling down to the air handler. They are all bunched together and taped every 6-8 inches making it difficult to tell which line is leaking.

There are three lines. A larger copper which is the suction lines and two smaller 3/8" copper lines one carries the refrigerant and one carries the condensation to be discharged outside. There is a condensate pump that pushes the condensation into one of the 3/8" lines.

My first instinct is the condensation line is leaking, because if the refrigerant line is leaking, the unit will not be cooling properly, but yet it is cooling fine, so I think it is the condensation line.

Regardless, I decided to cut two holes in the ceiling where the water stain is the most severe, where it indicates A and B below.



So once the ceiling is cut open, this is what I see indicating where water is dripping down from. It is almost impossible to tell which pipe is leaking because they are all wrapped together, and the suction line is insulated, so when water drips out of the edge of a tape, you can't tell which pipe it's coming out of. I can undo one tape I can reach but cannot undo all tapes to free the tubings from each other. Hard to even tell how many leaks there are as sometimes the leak may run along the outside of the pipes and drips 18" away where it's lower.





By the way there is no accessible attic space, flat roof so whatever I need to do needs to be done from below.

But a flashlight shining up I saw no stains further up, so definitely not roof leaks.

Next in order to isolate the condensate line, I cut the 3/8" condensate copper line about 12" below where it enters the ceiling. I then bend the condensate line to make a U turn to go down instead of up, ending in a 5 gallon bucket. This way when the AC runs the condensation is just emptying into the bucket instead.

I kept it running that way, and no more drips. I dried everything I can reach from the two holes, and observed, no more leaks. So now I am comfortable to say it's the condensation line. I think I see at least two pin holes on the copper.

Now I am trying to decide how to make the repair, and part of that is why pin holes on the condensation line?

You can see that both the refrigerant line and the condensate lines are the same copper tubing. The refrigerant line is always under pressure, the condensate line is not except occasionally water gets pushed past it when the pump turns on.

No leak at all for years and suddenly two holes. Why? Bad copper? I will say this, I visit the property every 30 days, and on the AC handler side, I change out the filter, and I pour a gallon of water/bleach mixture into the condensate line to clear it. Can the bleach be causing the pin holes in this copper? Are the soft copper tubing used in the AC trade thicker than the type M in water supply plumbing?

I am tempted to cut the tubing (if I can free the condensate tubing from the other two pipes enough to make a cut) and replace from there all the way back to the handler. The question is replace with what? This is a drain line for the condensation water.

Option 1: Get new 3/8" copper lines for AC and go from there back to the unit handler, I am guessing about 12' of length. How would I make the connection? I cannot solder there so close to the other lines. Are there compression or push in fitting I can use and I assume these must be special fittings for AC copper as the sizing is different?

Option 2: Run 3/8" vinyl hose from the cut back to the handler, the vinyl can be secured to the copper with tiny hose clamps. But is vinyl good enough to be in attic space? I understand vinyl may not be long lasting in the hot attic space, and may be too easy for rodent to chew through.

Option 3: the hardest way is to run a brand new 3/8" copper line from the air handler to the outside, using a completely different path, and not even deal with the existing piping inside the attic. This is not easy as it will involve exposed 3/8" as well as running through 8" concrete block wall and cutting holes in the exterior soffit that is thick plaster/lath.

Any other ideas also greatly appreciated.

Refrigeration copper tubing is equivalent to Type M plumbing copper. You can use plumbing compression fittings as long as you account for the different terminology, for example, 1/2 Plumbing copper and 5/8 ACR tubing are both 5/8 in OD. You can use the plumbing 3/8 compression fittings on your 3/8 OD ACR tubing.

Copper used for furnace condensate drain will pinhole because of the acidity in furnace condensate. But that should not be the case with AC condensate.

I made the repair but I am unsure whether I will go with this repair as a "permanent fix". I may take it apart and run a brand new copper line from inside to outside but that path involves much more destruction of ceiling and difficult to do while the unit is occupied so I am debating to do it now or wait till the current tenant moves out.

So first thing I did was I removed the leaked sections of the 3/8" soft copper tubing. It is a run through a chase and part of the attic a total of about 50' from inside to the outside. The leaks in the condensate line happened in the first 15' from the handler so that's what I replaced with a 3/8" vinyl tubing for now. I took the leaky section of copper and examined them carefully outdoor and saw some green copper corrosion around the pin holes like this.



I found four pin holes, to see them better I sanded the pipe clean with emery cloth.







I cut the tubing near the hole and found the tubing cross section to be fine, that it wasn't wore thin or anything, which is puzzling.

As you can see, on three of the holes there are some dark stains around the holes, why? Well that's where they taped the refrigerant line, the condensate line and the insulated suction lines together with these sticky tapes, as shown below. Could these tape be a problem something in the adhesives?





So now I have done the temp repair by replacing 15' of the 50' line with vinyl, I am worrying that the rest of the 35' may leak down the road. See the new 3/8" OD vinyl repair and the transition to old copper.







The most puzzling thing is as you see these pipes all taped together, they were ran at the same time many years ago. The refrigerant tubing and the condensate tubing looks the same, probably from the same coil...so why would the refrigerant line being constantly under pressure not leak but the condensate line line handling just condensation discharge pumped from a tiny pump leak in several places.

Could this be bad copper? My guess is these lines have been there for 30+ years and now the condensate line is leaking. Does it mean the refrigerant line is next to fail?

So now I have done the temp repair by replacing 15' of the 50' line with vinyl, I am worrying that the rest of the 35' may leak down the road.

So really my options are:

(1) go with the temporary vinyl repair and keep an eye on it for now.
(2) anticipate more leaks in the existing copper line downstream so abandon the vinyl repair and run a new continuously soft 3/8" copper tubing from handler pump to exterior.
(3) anticipate the refrigerant line will have the same fate sooner or later and run two new 3/8" copper tubing end to end if having to go through trouble to run one new line might as well run two.

I can't make up my mind on which way to go, and on top of that if I pick option 2 or 3, to do it now or do it when the tenant vacates which might be another six months (or even longer if he extends).

It is strange that the copper has not been eaten away from the inside around the holes. When furnace condensate copper tubing pinholes, the copper is paper thin around the holes and the tubing can be crushed by hand.

Here is a cut I made right where there was a pin hole, the thickness is uniform, does not appear to be thinner at all. I am not even sure if the corrosion if from inside out or outside in.