Does my brand new Heating/AC system use coils with dissimilar metals?


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Old 03-29-17, 03:05 PM
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Does my brand new Heating/AC system use coils with dissimilar metals?

I had my heating/AC system replaced yesterday in my house. It's the typical central split unit setup with air handler and evaporator in the attic. And the compressor and condenser outside on concrete slab.

I told installer that I don't want the aluminum fins and copper tubing coil arrangement in either unit because of the probability of galvanic corrosion with dissimilar metals. But I am getting different answers on what I have. I was told that the coils were all aluminum. And then after it was installed Carrier Corp. said it is aluminum and copper.

I have the model numbers and serial numbers below.

Carrier attic unit
Model# FB4CNP042
Serial# 1516A91469

Carrier outdoor unit
Model# 25HCE436A310
Serial# 1117E03168

So do I have aluminum fins and copper tubing for coils iin both units? Or do I have all aluminum coils on both units? I can't tell for sure when I look into equipment cabinet. Thanks
 
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Old 03-30-17, 03:39 AM
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I am not sure where you get the idea that aluminum fins and copper tubing are not compatible.
This combination is used in almost all fin-tube coils and has many decades of successful use.

The main problem with an aluminum finned coil is that the aluminum fin itself is subject to corrosion but only in a hostile environment.
Ocean coast and marine salt spray, industrial environments and some food service manufacturing could be an area where stainless steel or copper fins might be used but for sure not in residential HVAC and for sure not with aluminum tubing.
The only thing that could cause any problems with aluminum fins in a normal HVAC environment is if there was a mistake made with the use of the wrong cleaning products when servicing the unit .

The only one I could see promoting the idea of galvanic corrosion in dissimilar metal coils would be a manufacturer of an all aluminum coil.
This promotion is a way of justifying the use of aluminum tubing in a coil which is a cost saving measure for the mfr not protection against corrosion.
Copper is a far superior product for tubing than aluminum and this whole idea is a marketing trick, not a realistic problem.
 
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Old 03-30-17, 04:26 AM
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I have never had an issue with corrosion at the joints. But I have just had two leaks in one unit at those joints. Id much rather have the AL coil than a copper just because less issue with corrosion.
 
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Old 03-30-17, 08:59 AM
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Well, there is plenty of information on line about leaks associated with dissimilar copper and aluminum. Do they at least put some type of coating or sealant at the area where the copper is joined to the aluminum?

I live in Arizona where it's dry.

Another question. The outdoor unit cabinet doesn't have a whole lot of protection from foreign objects making contact with the coils. I mean a small rock could damage the coil or even a neighborhood cat or animal could screw around with it. There are bars with 1/4 inch spacing around the coils. Is there some type of mesh or screen I can wrap around the cabinet?
 
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Old 03-30-17, 01:27 PM
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Residential Bryant Fan Coil Systems 3 1/2 Ton | Carrier HVAC

That air handler has an aluminum coil and that heat pump has a copper coil.
I prefer all aluminum indoor coils. I have seen 3 year old coils with heavy rust on the tubesheets of the copper indoor coils. It is hot and humid in my neck of the woods.

This indoor coil was only 4 years old when I took this picture. (The company that installed it did not provide enough ductwork for a system that size, I think it was running near .9" WC)


I am not a big fan of all aluminum outdoor coils.
If I see an installation with aluminum indoor and outdoor coils and my gauges show an obvious leak in the system, I will always start with the outdoor coil. ( Trane) The leak is almost always in the same spot, near the location that copper transitions to aluminum and passes under the coil to the left of the gauge ports.


 

Last edited by Houston204; 03-30-17 at 02:33 PM.
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Old 03-30-17, 03:33 PM
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Carlos,

I'm confused. Are you saying my indoor unit has ALL aluminum coil and my outdoor unit has ALL copper coil? Or are you referring to the Bryant equipment you linked? When I look at my new outdoor unit I see copper tubing and silver colored fins. Does mine have dissimilar metals?
 
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Old 03-30-17, 03:57 PM
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Carrier and Bryant air handlers have the same model number. They use different stickers on the panel. It is the same air handler.

Your "indoor unit has an ALL aluminum coil".
Your outdoor unit has "dissimilar metals".

All aluminum outdoor coils are not as good as "dissimilar metals" outdoor coils.
I would not want one for my house. The spine fine coil is basically a wire brush that can be troublesome to clean if you have certain trees in your area or a shaggy dog or a drier that vents around the outdoor unit.



The instructor in a Trane class that I attended spoke of burning it off with fire to clean it. Something tells me that you would be uncomfortable if a service tech started burning your coil with a torch to clean it.

Carrier used to make "ALL aluminum" outdoor coils in the 80's. I have heard that they may bring it back but I hope it doesn't have the bristle type coil again.

Trane and American Standard are the only major manufacture making "ALL aluminum" outdoor coils these days. They still have some copper in them.

The hot gas line on the compressor would probably burst if it was aluminum.
 
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Old 03-30-17, 08:48 PM
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Yeah, my old Trane outdoor unit had the spine bristle coils. I got 22 years out of my Trane before I replaced the system two days ago. I gather from what you are all saying, that there may be pluses or minuses between aluminum and copper. And there could be leaks down the road in either arrangement.

I researched HVAC and this local contractor as best I could before replacing. I was also told that sub-standard installation is a huge factor in premature equipment failures and leaks.

I assume now that you don't think I made a poor choice in coil arrangement for my purchase.

I plan to clean the coils regularly like I did in the past.

Goofy as it sounds...................I might wrap some insect screen around the outdoor unit for added protection against foreign matter.

Hey thanks as usual for all your input. Believe me. More helpful than you realize.
 
 

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