Ok I know I said that Scrubbing Bubbles is my BFF, but I guess that makes my AC my blood brother
May 17, 2010 7:41 PM   Subscribe

Portable air conditioner works fine, but now developed a rhythmic thrumming noise. Tilting it to the left, and only to the left, by raising the right side ~2cm/1" alleviates problem and gets better airflow...

I'm terribly heat adverse and my two best purchases in the last decade was LASIK and my portable air conditioner. I'm currently more poor than usual and am completely unable to afford to buy a new air conditioner.

It's a portable unit, works great, but after setting it up and breaking it in, a month ago, I just turned it on for the second time this season. Startup is fine, but after getting warmed up, it makes a rhythmic thrumming sound (about 1-1.5 Hz). There's still airflow, and it's cold. I've tried the high and low settings with and without "CoolJet" (it's like a turbo/afterburner where it vapourizes more water to make the air colder).

Tilting the unit to the left alleviates the noise and I get slightly better airflow.

I've vacuumed out the unit, made sure the water is where the water is supposed to be, made sure all the housing and hoses and parts are secure.

I currently have a couple of paperback books propping the unit so it tilts a little to the left.

Can anyone diagnose the source of the problem, if there is anything I can do to fix it myself, and if running the unit tilted to the left is going to be detrimental to it?

My guess is the coolant leak is adding up... if that's the case, is there any DIY coolant top-up methods, or if it's something that a repair shop can do without costing a leg in addition to an arm?

posted by porpoise to Home & Garden (5 answers total)
Best answer: I guess this isn't a window unit? Rhythmic thrumming says to me non-engineer mind that the fan bearing is misaligned or busted.
posted by Inspector.Gadget at 7:52 PM on May 17, 2010

Response by poster: Not a wall unit. It's Pinguino portable [gis].

As a fellow non-engineer, but a computer enthusiast who's seen lots of ways that (small) fans fail, although it sounds similar, the (temporary?) solution doesn't seem to indicate a fan problem. I thought at first that it was a loose part responding to resonance but it doesn't seem to be the case.

(Un?)Related question - is "thrumming" a real word? I've searched using noise/thrumming/sound/other-words in both google and youtube and haven't ran into someone else publicizing a similar problem. Is there a better/correct word to describe the mmmmMMMMmm......mmmmMMMMmm...mmmmMMMMmm.... sound, on top of the normal shhshhshhshhshhshh sound that it makes?

I've had it running for another couple of hours, tilted, and it seems to be fine/stable. The outside has cooled enough that I've turned the thing off and have an open patio door now. I know that this is a very trivial matter in the grand scheme of things, but this AC is one of the few things that let me make it through 4 months of the year without going on a killing spree*/being even more insufferable than I already am.

*Hyperbole - the heat is a barrier to my starting a killing spree due to it destroying any motivation for me to be active; if it happened, the spree would start and end with my own self-inflicted death
posted by porpoise at 9:33 PM on May 17, 2010

Best answer: A portable air conditioner will contain a compressor, which will be a sealed unit, and a fan which won't be. My guess is that the fan bearings have dried out or got a little gummy while the unit's been unused, that the fan is now running a few RPM slower as a consequence, and that some harmonic of the vibrations induced by the fan are now within 1Hz of some harmonic of those induced by the compressor. The thrumming will be the resulting beat note. Tilting the unit is probably enough to alter the two rotational speeds enough to shift the beat to inaudibility.

Lubricating the fan bearing might help.
posted by flabdablet at 11:27 PM on May 17, 2010

Best answer: Also: fans in this kind of equipment are generally powered by smallish shaded-pole induction motors, and these will not blow up quickly when stalled; so once it's warmed up to the point where you hear the thrumming, try powering the unit down, jamming the fan blades with a wodge of cardboard and powering it back up again. If the thrumming is still there, it's coming solely from the compressor and your tilt method will probably remain your cheapest option for dealing with it.

If you're running it with a jammed fan and you start to smell hot motor windings, just switch it off and unjam the fan. The motor will then cool down again fairly quickly (probably quicker if it's spinning).
posted by flabdablet at 11:32 PM on May 17, 2010

Response by poster: Huh, it was the fan afterall, and not a compressor issue.

Damned if I can get at the fan assembly to lubricate the darned thing (grumble grumble not designed to be user serviced grumble).

Thanks flabdablet!
posted by porpoise at 6:19 PM on May 18, 2010

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