"A" Frame Evaporator Coil Question

[Wayne Boatwright]

We have an almost two year old electric furnace/air conditioning unit with an "A" frame style evaporator coil mounted in the air handler section of the furnace. The evaporator coil sits in a very heavy guage plastic or composite condensate collection pan with excellent drainage, and as far as I can see, there is no metal to metal contact from the evaporator to other components.

We change our air filters every 2-3 months, since we live in the Arizona desert our cooling season is much longer than in more moderate climates. The interior of this area appears to be extremely clean.

The last couple of times we changed the filters, I noticed that the bottom of the evaporator frame that sits in the collection pan is showing rust. The frame material appears to be galvanized steel. Obviously, I know that water causes and/or accelerates rust.

What I'm wondering is if this is "normal", and if it's not, what measures should/could be taken to remedy the situation. Since the unit is so new, I'm mostly concerned about the longevity of the evaporator unit.

TIA for any opinions or suggestions.

[Tony Hwang]

Hi, One thing comes to mind. Is your system properly matched for you house size? Oversized system short cycles and does not remove humidity very well.

[Wayne Boatwright]

On Thu 09 Oct 2008 11:16:38p, Tony Hwang told us...

I believe it's properly sized for the house. It doesn't short cycle, and the air is very comfortable in the house, although I've never actually checked the humidity level. I've been in spaces where the air felt damp and the units were obviously not right for the space.

Thanks!

[Pete C.]

During cooling operation the A coil will be covered with and dripping condensation. The frame is galvanized steel, but the holes where the lines go through are typically punched in the pre-galvanized sheet. This punching leaves a small amount of the steel on the edge of the punches without the galvanizing and this is where a little bit of rust will trickle from. Since the lines are copper and the fins are aluminum, they are not affected by the condensation. We'll all be long gone by the time the rust on the frame could ever reach a point where it would be a problem.

[Ralph Mowery]

Does the Arizona desert have enough humidity that would be an issue ?

[wayneboatwright]

Thanks, Pete. That's reassuring!

Wayne

[wayneboatwright]

Probably not. Except during our monsoon season in July and August, our relative humidity rarely exceeds 10-13%. During monsoon season the humidity is probably averages no more than 60-65%.

Wayne

[Steve Barker DLT]

What in the flying f*ck does that have to do with his a-coil frame rusting?

s

[Stormin Mormon]

Well, if Tony posts a couple more off topic answers like that, he might be a charter member of the "Mile High" club, having been giving a flying f*ck?

The very shaky and vague connection is that a poorly sized AC system may take more or less humidity out of the air. And will be more or less likely to keep the A coil wet all the time. I don't think there's a lot of connection. A badly sized system won't dehumidify, which means the water remains in the air, which means less water to rust the coil.

Tony may not be very well connected?

[Snoopy]

I have had 1 unit rust after 12 years now this unit is already rusted after only

6 years. Is there are unit that will not rust?

[hrhofmann]

I don't think that I would worry about rust. There are so many other things in a heating/air conditioning system that can (and do) go bad that some rust on the bottom of the A-coil is WAY down on my worry list.

[trader4]

Kind of what I was thinking too. Some rust at 6 years doesn't sound that bad. It depends on how much rust. If it has some rusting and will last another decade+, why worry about it now? Nothing that can be done, short of replacing it anyway.

[Ed Pawlowski]

What's rusting? The coils are made from aluminum and sometimes copper. That does not rust. Steel housings can rust and can be cleaned and painted.