cleaning air conditioner condenser unit

"Ingredient: SODIUM HYDROXIDE" - eats aluminium (we have an extra "i").

Thank you for your reply.

Is the aqueous NaOH still likely to damage aluminum at a concentration of less than 0.5% (as per the MSDS), with a maximum contact time of 2 minutes, with a film of dirt/grime coating the aluminum fins?

My neighbor said that after cleaning with 409, the condenser fins "looked like new". I'm trying to decide if the risk is worth it, or if I should just settle for some liquid detergent soap (without NaOH) and clean that way...

I'm still not certain whether or not the fins are aluminum. Is aluminum the standard material of construction for air conditioner condensing units? The metal looks black... could be the dirt, though...

and shorten the life of the unit, while cleaning. You could sandblast the fins in order to clean them, too - obviously that does a better job cleaning than 409 and it damages the condenser even more.

Condensers lose efficiency environmentally because of blocked airflow and from built-up residue on the fins (automobile/industrial/trees-and-plant oil/road salt/wax/rosin vapors in the air)

Brush off the plant matter with a soft brush - then I would suggest you go to Dey or a like appliance parts store and get a waterless spray cleaner specially designed for aluminum cooling fins.

Use water.

Hot water if you have a buildup on oil or grease, otherwise just water.

Check around MSDSs until you find a butyl product that doesn't have lye. The Home Depot "Zep" store brand (the blue jugs, not the "industrial strength" purple) used to not contain lye.

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This one gets my vote. Perhaps with a detergent like "Dawn" added. Preferably with a physical contacting agent like a long bristle brush. Non-contact sprays don't release all the adherent soil, as you will notice if you compare spraying your wheel rims, versus brushing them.

Brian Whatcott

If you can use water, why not a pressure washer?

Detergents use salts as ionizing agents - salts attack aluminum, and they collect in the crevices and joints and that concentrate their effects - soft water, and harden water, also contain salts.

Soap/cleaners used for large aluminum curtainwall structures use soap made without salts - ( I had aluminum rated cleaning soaps made in 2000 gallon batches at Ecolabs in St Paul, MN. The difference in the life of the surfaces in NYC was about three times as long when using only the non-ionized soaps.)

Use a cleaner rated for aluminum fins - they are either tri-chlor based or they are made with distilled water and no salt-based ionizers.

Does anyone know if the residue of any of these cleaning even approaches the corrosive effects of organic matter decaying in acid rainwater?

Fair question - some condensers I have seen lately have very fine aluminum fins in a close spiral - I could see these being flattened by an incautious high-pressure spray gun.

Brian Whatcott Altus, OK

Surface finish would be a particular concern with mirror-surface aluminum sheets, I agree.

One of those useless memory factoids that stuck in my mind was the use of "Dawn" for de-oiling damaged sea-birds at the Exxon Valdez disaster, hence the prejudice that is is relatively benign.

Brian Whatcott Altus, OK