Portable AC busted or just overworked?
July 6, 2021 2:25 PM   Subscribe

We bought a new portable AC to cool my attic office, but it’s blowing hot air instead of cool air. I probably should have sized up even more to account for attic heat, but is blowing hot air a sign that the unit is defective, or just not able to cool the space?

We noticed the issue almost immediately, but things improved a bit when we shortened the exhaust tube as much as we could. However, after an hour or so it was back to blowing warm air again.

The problem is that the eaves of our attic are uninsulated, so they leak heat into the room. The unit is the smallest available, but it is still supposed to support double the dimensions of my office.

I’m not necessarily surprised that it’s not doing a great job of cooling the room, but it is surprising that it doesn’t seem to trying. Larger portable units will have to be shipped—and be too powerful for our guest room downstairs which is one of the reasons we went portable—so I’d like to know if this unit is just defective and needs to be returned.

Anything I should try before returning it? Should I start it earlier tomorrow so it’s keeping up with the heat instead of trying to cool things down?
posted by thecaddy to Home & Garden (10 answers total)
Best answer: Try it in the smaller guest room. That should tell you if the problem is the size of the room or the unit itself.
posted by soelo at 2:43 PM on July 6, 2021

Best answer: It should at least outputting noticibly cool air.

Is the compressor even running? There is usually a sound when it starts that is fairly distrinctive and louder than just the fan.

Quick things to try if it isn't. You may have it set to fan only or the tempature is set too high.

If you had stored the unit on it's side or upside down, it should sit upside right for 24 hours before being run as the coolant can get out of place.

Turning it off energy saver or other energy efficient sounding setting might get it to kick in.

If you've checked all that and it still isn't running, the unit is defective so go ahead and return it.
posted by AlexiaSky at 2:44 PM on July 6, 2021 [5 favorites]

Technology Connections: All about portable air conditioners
posted by Rash at 2:46 PM on July 6, 2021 [1 favorite]

Does it have one hose or two? The single-hose ones draw air from the room itself, push heat into it, and exhaust that out the hose. For obvious reasons this doesn't work well when the room is already very hot (cool air can hold more heat than hot air). The ones with two hoses draw in outside air instead, and generally work better. Try one of those (but read the reviews first; some of them are poor performers or are unreliable. It could be defective but I lean toward just not the right tool for the job.

You should basically ignore how much square footage the specs say the unit will cool. That will vary wildly based on the temperature differential, how fast the heat is getting into the room, and how fast the cold air is escaping. It's more of a best-case scenario: it's not too much warmer in the room than you want it to be and the space is well-insulated. An attic is basically the worst case scenario for a portable A/C unit. At least our attic would be.

You will generally be happier with portable A/C units if you think of them as machines that can blow coolish air directly on to you, rather than as machines that can lower a whole room's temperature to a comfortable level. We had three of these stupid machines running during the Great Seattle Heat Dome of 2021, and hung curtains to trap the cool air in one room, and put aluminum foil on our windows, and it still got into the 90s in the room in the early evening.
posted by kindall at 2:50 PM on July 6, 2021 [2 favorites]

Best answer: So I'll offer this: I have a portable air conditioner and it has three modes: A/C, fan only, dehumidifier only. They are labeled with what I find to be inscrutable symbols instead of words and it's extremely easy to toggle between the three modes by accident especially when moving the unit around (e.g. when you shortened the tube).

Also single-tube A/Cs just don't work as well as double tube. We have one of each style (bought one, thrifted one) and I definitely need to set the single-tube to 75 to get it to about 80, and start it early to "keep the room cool" rather than "cool it down."
posted by holyrood at 2:51 PM on July 6, 2021 [3 favorites]

Best answer: A properly functioning AC unit will always blow air into the room that is colder than ambient, even if it can't maintain the set temperature. I'd read your AC's manual very closely to ensure you have it set up correctly, and if it persists after you've ensured it is, I'd look at getting a return on it.
posted by Aleyn at 8:39 PM on July 6, 2021

If you can give us the name and model we may be able to look up some information.

I am assuming you did get a true AC, not a "swamp cooler".
posted by kschang at 10:34 PM on July 6, 2021 [1 favorite]

Best answer: This doesn't seem right; I think your unit is either defective or isn't on the right setting. I've used portable A/C units (single tube models) in an upstairs bedroom and guest room/office for 2 years now and they work well. And I have a similar issue with the upstairs actually being a former attic with large eaves/crawlspaces. It gets insanely hot up there especially if the sun is out and beating down on the roof. But even in the rather large bedroom, the temp drops immediately once we turn the A/C on and the air blowing out of it is always quite cold. We don't run it in the bedroom throughout the day, so it can be pretty hot in there before we kick it on a little while before bedtime.
posted by misskaz at 7:54 AM on July 7, 2021

Response by poster: Thanks all! I let it rest overnight and tried it again the next morning; even though I could hear the compressor kick in there still wasn’t any change in the temperature.

We returned it for a better model this weekend (one that can be converted into a dual tube model if necessary). It’s actually blowing cool air and the space isn’t perfect, but it’s a lot better than it was without the AC.
posted by thecaddy at 2:29 PM on July 12, 2021 [1 favorite]

Response by poster: Also for anyone reading this in the future

posted by thecaddy at 5:08 PM on July 14, 2021

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