Repairing copper coil in central A/C unit - HVAC question

Factual Questions
1

What have I done, and am I in for a world of hurt to fix it?

Without going into all the detail, I made a stupid mistake and ended up nicking a copper tube inside my central A/C unit (in the plenum above the furnace - so the inside heat exchanger portion) with a drill bit. Of course, it was enough of a nick to cause a leak.

Now all the refrigerant is gone, and I have a copper tube in a heat exchanger that needs repair, followed by a recharge of the entire unit.

So I guess my question is whether this is repairable - and how easily can it be repaired. I’m going to leave this to the pro’s (I have an appt for someone to come out tomorrow) - I know that I have backed myself into a corner that I cannot get out of without help. I’m just trying to gauge whether it’ll be a relatively cheap fix or not. I’m scared that the worst case scenario - total replacement of the entire heat exchanger inside the house - will be necessary. However, I figure that this kind of stuff must happen regularly enough that it seems very likely there would be a less intense (and cheaper) repair option available.

For those who might be HVAC professionals - just to give some more detail: The heat exchanger in the unit is in a pyramid shape, and it looks like the refrigerant tube runs back and forth from top to bottom. The nick is on one of the 180 degree bends. The best I can come up with for a description of the damage is if you were to take a normal sized flathead screwdriver, and hammer it against a copper tube. There is definately some misshapen tube that got bent inwards, and (obviously) a portion has pierced through. It was enough of a leak that all the refrigerant had leaked out within 12 hours. Are those bends something that can simply be cut off, and new tube soldered back on in place? Perhaps it depends on the unit - maybe the copper bends were soldered in in the first place, and they can be easily removed and replaced.
I just dont know what is typical for designs of these things.

Thanks for any words of wisdom and knowledge.

2

It should be an easy fix - the AC guy will just hard solder a patch over the nick, pump it down and recharge. Of course, he’ll take this as the perfect opportunity to sell you a new AC…

3

That would be AWESOME if the fix can be done that easily.

The unit is only 2 years old, so if he tries to sell me a new one, he’ll get a serious :dubious:

Thanks for the encouraging response.

4

That “heat exchanger” is an “evaporator coil.” The only thing tricky about this is that the leak is in a “U tube”, and the cooper in the U tubes are often paper thin. The tech will not remove the U tube but braze over it; essentially patching it.

From there a qualified tech should pressure test it with dry nitrogen to make sure the patch is good, and there are no other leaks. From there a vacuum pump is put into use to “evacuate” any/all air and moisture. Then it is recharged with new Freon.

In my neck of the woods:
$28 per per pound of Freon. (ranges between $20-35), and there is typically 1.5 to 3 pounds of Freon per ton. Look at your model number outside and there will be some factor of “6” in the model number, as there is 12,000 (12) btus in a ton. For example, if there is a “24” in the model number you have a 2 ton; “30” is 2.5 ton, “36” is 3 tons etc.

So…a 3 ton unit has maybe 4.5 to 9 pounds of Freon in it------at $28/pound. Look at your information outside, because many units will list “the factory charge” on the nameplate, that will tell you approximately how much freon this unit holds. So, here’s my internet bill:

3 ton unit; 3 tons x 2 pounds per ton = 6 pounds x $28/ton = $168 Freon
Brazing rod, gas, nitrogen, etc $20

Travel .5 hrs at $70 $35
1.5 hrs on site @ $70 $105
Vehicle cost $25

Total bill: $356

Now prices vary wildly, so your bill may be higher or lower than this. In fact, my bill might be lower if the repair was simple or the unit takes less freon. But that’s my best internet guess.

5

Yeah I figured there would be a good deal of variance in the price.

My unit is 2.5 ton. I checked the placard this morning and saw that it came charged from the factory. The only number I saw was 1.6 Kg - which at the time seemed unlikely - but now that I think of the conversion factor, I realize that its 2.2 lbs per kilogram, not the other way around.

(As I get older, I forget a little more each and every day. I’m only 32 - I got a lot of forgetting to do!)

Anyhow, I didn’t spend a whole lot of time looking (it was raining and I was dressed up for work) - so its possible the 1.6 Kg referred to something else. However, that is is the right ballpark at 3.5 lbs, if a little shy. Your estimates for labor and overhead seem to be in the ballpark for what they will charge me for the service call - so I find your cost estimate to be useful as well. Thank you.

(and ya know - I thought maybe the copper on those tubes was very thin. I’ve dealt with copper pipe before in sweating connections, and as soon as the damage was done I thought to myself ‘damn those tubes must be thin as hell because I didn’t hit it nearly hard enough to go through the schedule M pipe I’ve used in the past!’)

So this will be a nice $200+ lesson learned. I hate these kinds of lessons because they usually come down to stupidity on my part and not taking a second to think something through. I’ll end up telling myself I’m still ahead of the game because I recently did about $3000 worth of suspension work on my car for the cost of $500 in parts and a weekend of labor.

6

Good luck!

Let us know how it turns out.

7

So someone came to look at it.

He basically said that trying to patch over or braze the hole in the copper bend would be a useless effort. He said it would just make the hole bigger, and that even if he could get a patch over it (being on the bend makes it more difficult), the possibility of it leaking would be very high, and then in a year or two I’m back in the same boat.

So he wants to sell me a new coil.

It seems shady to me. I mean - this sort of thing has to happen often enough that the solution cannot be to replace the coil every time.

Also - he was saying it would cost about $90/lb to recharge the system with R-22. That seems a bit high, even for geographical differences (I’m in eastern MA, btw - so who knows).

8

He should be willing to provide a warranty with a new coil. Doesn’t sound like he would do that with a patch, and a second service call won’t make anyone involved happy.

The R-22 sounds high, but does it include the time/steps necessary to charge the system? He may just charge a flat rate per pound on small jobs that include his time.

9

As a raw material, $90 per pound for either R22 or R410 is outrageous, but more likely, that includes the labor of pumping down the system, leak testing and re-filling. All of the equipment needed to do this is expensive, so it’s part of the price.

As a raw part, a 2.5 ton “uncased” (ie: naked) evaporator coil is in the $200-300 range.

As you’ve learned, A-coils are supremely fragile things, and repairing them can be iffy, regardless of their age. Have you called anyone else for a second opinion yet?

10

I haven’t gotten a second official opinion yet.

The $1500 includes the new coil, and all the service to patch it in and recharge the system.

The price of $90/lb was the response when I asked about just recharging. I didn’t confirm, but it sounds likely that the cost includes labor, equipment, etc. In other words, flat rate of about $400 for recharging a system that takes 4 lbs of R-22.

Fortunately its not the cooling season, so I have some time to figure things out a bit more. I’d like to find some old-timer who knows every trick in the book and can fix it in place, but from what I gather, even if it can be fixed it more then likely requires have the whole coil out and on a work bench.

My father in law’s coworker does a lot of A/C stuff and has quite a bit of experience (as FIL says - if he can’t fix it, noone can). He told us that if we can get the coil to him, he can give it his best shot at fixing it - but until he sees the thing himself, there’s no way to be sure. If he can fix it, then we would have to have someone out in the spring to rebraze the in/out connections, and recharge.

I just dont want to make things worse at this point - but I suppose if the coil ends up needing replacement anyway - those in/out connections will be necessary no matter what.

Why are these coils so damn fragile? I mean - its one thing for a DIY’r to screw up and have to pay for their mistake - but I have to believe that even pro’s ding those copper U-bends once in a while at job sites for whatever stupid reasons. It just seems to me that its a rather poor design if the best option is replacement.

11

Because copper is expensive. Profitability of AC manufacturers took a big hit when the cost of raw materials like steel and copper went up a few years ago. Plus, they are usually protected from drill bits by the air handler housing.

12

If it were me, I’d call around until I found an A/C guy willing to try a patch. Explain to him upfront (maybe send some digital photos) where the hole is.
It’s probably going to require some skill, but it shouldn’t be impossible to do. Besides, it’s already broken - what do you have to lose by trying to patch it?

13

The guy is being a bit of a prick. I install ductwork for a living. LU 28 NYC Sheet Metal Worker. I install the A/C units “50/50” with the Steamfitters, LU 638.( 2 Sheet Metal Workers, 2 Steamfitters). The steamfitters hook up the copper, I hook up the duct work. My father told me “Your not a real “Tinknocker” untill you hit a coil!” I put a tex-screw into a coil a few times; and the fitter simple solders the hole closed. This has happend on small A/C units, feeding like 2 rooms; so the coil would be about the same thickness as yours. He is just trying to get more money out of you for an easy job.

The worst was actually my partner, all 8 screws from the duct connection hit the coil. We had to go back and reinstall the duct they took down to repair the unit. I say it was a bad design to have the coil about 1/16 of an inch from the discharge of the unit.

14

If I was in the field I would not give any warranty for a hack job. The A coil is fragle for several reasons. Origonal cost. Thinner copper will have a better heat transfer rate among the most common.

Depending on the size of hole, location, and construction of the A coil will determine if it can be repaired.

From earlier posts I was thinking you were in for an expensive repair.

15

Don’t talk to this guy again. gotpasswords (who I think is in the business) was right; the wholesale cost of a new coil is $250-300. With markup, labor, misc materials we would sell this (in SW Ohio) for $7-800 and that includes new Freon. $1500 seems outrageous no matter where you are.

The U tubes on coils have been paper thin forever. Soldering them is trickier that a leak on the “lineset” because the copper on them is much thicker.

To solder a hole in a U tube requires a filler metal other than [soft] solder. (products like “Stay Bright 8”, or “50-50.”) Soft solder has a very low melting point and so propane or mapp gas can be used. But not in this case.

When it’s a hole, most often you have to use “brazing rod” as a filler metal. That requires acetylene or oxy/acetylene, not propane. The filler metal will not “liquify” until it hits around 1400F. (and propane doesn’t burn that hot)

The problem is, the melting point of your brazing rod is close to the point you’d melt the [paper thin] U tube. It’s certainly not impossible (I’ve done it many times) but it requires a guy with a little experience in brazing. It’s the same process as fixing any other leak, just a little trickier because of the wall thickness on the U tube.

Keep calling to you get someone who will talk some sense.

I also see no reason to remove the coil unless access is difficult. This will only increase costs. Fix it in place unless there is no other option.

16

You do not use soft sodder on a AC system unless you want it to come apart.

17

I wouldn’t use sodder on anything.

18

I use oxy-MAPP for brazing. The stuff is much easier and safer to handle or store, plus it burns nearly as hot as oxy-acet. On the downside, unburnt MAPP stinks.

19

Doesn’t stop people from using it who should know better.

A word of warning. If you get any weld work done on the system, check to make sure you’ve got a filter downstream before you get to your compressor. If any metal shavings or solder gets to the compressor it can destroy the valves and require a complete replacement.

20

I used to believe this, however I went to a brazing class given by the JW Harris Company, the people who make “Dynaflow”, and “Sta-Bright 8”, two of the most common products in brazing/soldering.

We took a 1 1/8" piece of ACR hard copper about 10" long and brazed (with Dynaflow & oxy/acetylene) a cap on one end and soft soldered (with Sta-Bright 8 and propane) a male adapter on the other end.

We took the finished pipe and put in a hydraulic chamber with clear plexiglass and pumped it until it burst. In every single test the pipe burst near the brazed cap. Every Single Time.

The burst pressure was around 3000psi. (this was either “L” or “K” thickness) I brazed two of them back together and they burst again around 1800 psi. (the hole was around the size of a dime; a tear)

The engineer explained to us that the heat of the oxy/acetylene weakens the copper sufficiently that it will always burst there.

On top of that, I asked the engineer about oxidation. When you braze the pipe oxidizes and there is flaking and discoloring etc. the exact same thing is happening inside the pipe and that oxidation is potentially harmful to the A/C system.

I also took a test to be certified in brazing/soldering some years ago. The tensile strength------the strength to pull apart a soldered joint was around 30,000 psi if I remember correctly.

So I continued to quiz the engineer:

"It seems to me that soft soldering produces:

  1. Superior bursting strength
  2. Superior tensile strength, and most importantly,
  3. No polluting of the inside of the refrigeration system

Doesn’t that mean that overall soft soldering with propane is a superior connection?"

He said, in his view, definitely yes.

Now I’ve asked this question dozens of times in the years that have passed, and I’ve heard nothing that disputes it. My experience is that for patching, or large holes, or for older, particularly sloppy fittings brazing is the way to go.

But a new system with new lineset and fittings? IMO Sta-Bright 8 with propane is a superior connection.