Can you paint an AC condenser?

[MidModCad]

As you can see my condenser is coated with some surface rust that I'd like to paint over. There are threads everywhere on the topic, some saying it will negatively affect heat exchange - others claiming the effect is negligible.  Anyone try it and get a good result?

[Highwayman68]

They come painted when new and many have repainted old ones when repaired. You are fine to paint it.

[MidModCad]

Thanks. Rustless is a much better look. The finish looks semi-flat or semi-gloss.  Any idea which is correct?

[The Tassie Devil(le)]

You definitely want a flat paint, as anything glossy will reflect heat, and thereby limit the operation of the cooling effect.

Just don't apply too much paint.

Bruce.

[MidModCad]

High temp paint?

[Macabry]

Matt black high temp rattle can is your best bet ... just thoroughly degrease it and key with scotchpad first and it'll go on and stay on ... as tassie said, not too thick ... less is more

Good luck

[David Greenburg]

I seem to recall seeing special radiator paint that is particularly thin in order to minimize interference with heat transfer.  Perhaps it was Eastwood?

["Cadillac Kid" Greg Surfas 15364]

That rust acts like insulation on the condenser fins reducing its capacity to transfer heat. Painting over it just adds more insulation if the rust remains. Can't see how bad the rust is but if it is just surface rust some time with a small soft bristle brush will be time well spent.
Greg Surfas

[The Tassie Devil(le)]

I very much doubt that there is rust there as these components are Aluminium, and Aluminium doesn't rust.

Could it be simply dirty water staining from an overflowing radiator?   I know that that horrible old coolant fluid stain is hard to remove.

Bruce.

[MidModCad]

Looks like rust to me, guys.  I'll post a close up tomorrow.

[35-709]

   Take a magnet with you.

[MidModCad]

As you can see - and a magnet verifies - it is definitely rust. The photo was taken after a light pass with a copper wire brush. If I paint over the rust I'm thinking it will likely return. I could give it a light sand but there's a chance the particles will clog up the fins, yes?

[2manycars]

Original Air in Tampa rehabbed mine for me. It is painted a gloss black. I don't know what specific paint they used.

[MidModCad]

Kinda out of my geographical area, but thanks for the suggestion. 

[2manycars]

Eastwood radiator paint in gloss black might do the trick for you.

[MidModCad]

Think it would seal the rust to some degree?

[V63]

As you can see - and a magnet verifies - it is definitely rust. The photo was taken after a light pass with a copper wire brush. If I paint over the rust I'm thinking it will likely return. I could give it a light sand but there's a chance the particles will clog up the fins, yes?

The early condensers were steel and painted. I want to say 1963 was first year for aluminum? It was also painted. I had a 1962 (new A6 compressor design) and just can't remember if it was aluminum ? But I'll default to 1963.

["Cadillac Kid" Greg Surfas 15364]

If this were me and I know it's not, I would take a toothbrush sized brass bristle
Brush and gently go horizontally along the tubes to knock the surface rust off. Then with a large soft bristle brush again gently brush the fins. Blow any loose dirt
And rust off and paint with Eastwood's radiator paint.
Greg Surfas

[Macabry]

I agree with Greg regarding using wire brushes to gently remove the "active" rust, then I'd wash it down with solvents or carb cleaner ... regarding painting though, I would suggest a high temperature paint either matte or gloss (your decision), but I would definitely use a spray/rattle can rather than brush on paint and DO NOT worry about using radiator specific paints and heat transfer ... I'll explain:

I've performed extensive testing on oil coolers and radiators over 20 years or so using different paint/application methods and heat conduction ... I have a trusty old IR thermometer and mercury thermometer that I've used to test painted surfaces.  I have NEVER seen a difference in conduction measurable by using a specific "radiator" paint (as sometimes claimed), the biggest issue I've found has been the effect of thick/uneven paint on surface finish longevity. Yes, very very thick paint will affect conduction but only minimally. The bigger issue is the heat cycles (contraction and expansion) causes flaking over time on thick paint this effect is worse/quicker... I suggest a light spray painting and try to ensure it doesn't build up in the edges/valleys of the fins. Once the piece is cleaned and prepped well this should give years of happy service 

Oh, and gloss/matte paint seems to make no difference

In case anyone's interested this was tested on Model A ford radiators, Ford Anglia e494a, Reliant 3 wheeler radiators(awful little cars) and most often Citroën 2cv oil coolers

[MidModCad]

Just saw this post, and great info!  Fortunately, I did everything exactly as you advised and it seemed to come out well.  I also added a light sanding with 400 which took some rust off the horizontal fins. Fingers crossed no flaking over time.