A 120V air conditioner with a 240V outlet
June 5, 2008 3:12 PM   Subscribe

Given constraints, how can I make a 120V window air conditioner work on a 240V outlet?

I'm breaking down and getting a window air conditioner for my apartment this year. It's ~500 sq. ft., so I'm thinking ~10,000BTU should be good. All fine and dandy; I can get a Frigidaire at the local Lowes for $200 and some change.

The problem comes with power. The only 120V outlet by the window is not grounded, and is on the same circuit as the fridge and microwave. Bad situation! But I also have a 240V outlet for the baseboard heater (NEMA 6-15R or 6-30R plug). Perfect... now how do I make this work?

I looked at a couple 240V air conditioners and they're all either (a) too powerful or (b) too expensive. I even had a co-worker who's also a landlord help me search, and we came up with bupkis. Plus, a 120V unit would be more flexible for future living situations. So getting a 240V unit is out of the question, unless I can find one relatively cheap.

Changing the outlet wiring is also not feasible. I'm moving in 2 months, and frankly my landlord is very slow getting around to requests. I just want to be comfortable for 2 months without a ton of hassle.

So, I've been looking at step down transformers. A 3,000 watt one should easily do the trick. The air conditioner is around a 1,000 IIRC, so this gives it some wiggle room for when the fan or compressor motors start. But this introduces a problem with plug types! Every one I found seems to assume I'm plugging into European outlets, or it doesn't have an option for the 6-30R american outlet.

Any advice? Do I really have to create my own custom patch cable from european to american?
posted by sbutler to Home & Garden (19 answers total) 1 user marked this as a favorite
IA totally NA Electrician, but if you have access to the circuit breaker, this could be a snap. In my very limited experience, a 240v outlet simply has TWO hot wires in addition to the neutral and ground wires running into the receptacle.

Kill the circuit, pop the device (240v jack) out, tape off one hot wire and connect a regular outlet device in its place, using the one hot wire, plus neutral and ground. Shouldn't take more than five minutes, and just as quick of a replacement when your time's up.
posted by Aquaman at 3:19 PM on June 5, 2008

On second thought, use a wire nut (plastic cone thingy) AND tape to cap off the second hot wire.
posted by Aquaman at 3:21 PM on June 5, 2008

A 240V outlet like that is a ground plus two hot wires which are out of phase with each other making 240V across them - they're only 120V from ground though. So All you have to do is wire a standard outlet with ground & neutral to the ground on that outlet and the hot to either one of the hot outlets on the 240V plug. You don't have to rewire the existing outlet - just buy a 240V plug, a box, a standard outlet and some wire and you should be good to go.

Note: this assume you know how to properly do home wiring. If you don't, please go get an actual electrician so you don't kill yourself or start a fire.
posted by GuyZero at 3:24 PM on June 5, 2008

You need to replace the breaker as well. This is a job best left to an electrician.
posted by caddis at 3:30 PM on June 5, 2008

You can't do this without running new wire from the panel to the outlet. The reason is base board heaters don't make use of a neutral which your A/C needs.
posted by Mitheral at 3:33 PM on June 5, 2008

I'm pretty sure that a 240V outlet has the proper neutral. However you do need to replace the breaker, per caddis' advice. This is a little like getting medical advice off the internet - you'r really better off getting a professional to fix this for you.
posted by GuyZero at 3:35 PM on June 5, 2008

Best answer: For two months I'd recomend getting a grotesque sized extension cord - really, really thick and no longer than you absolutely need - and using that with a different outlet. Did I mention really thick?
posted by Kid Charlemagne at 3:41 PM on June 5, 2008 [1 favorite]

Wow, I just read what GZ wrote more carefully. Yikes. Don't do that. You will not have a neutral wire. Plus, as I said before you will not have a proper breaker. Breakers are there to save your dwelling from fire. Don't take chances there.

(on preview - this is being addressed. nevertheless, for a proper job you need to rewire one hot wire in the panel, run a neutral wire if it is not present, and it likely isn't, replace the breaker with a proper 120 breaker, and replace the outlet with a proper 120 outlet. Working in the panel is not for the inexperienced. Please hire a pro for this.)

(By the way, when did "Related Questions" get implemented? Very cool.)
posted by caddis at 3:45 PM on June 5, 2008 [1 favorite]

Best answer: Seconding Kid Charlemagne. Air conditioners are one of the many things they say you shouldn't hook up to an extension cord, but you actually can, as long as your extension cord is heavy enough. Find an outlet on an otherwise unused (or mostly unused) circuit, and check the breaker panel for that circuit. If it has a 15 amp breaker, get a 15 amp extension cord. 20 amp breaker, 20 amp cord. Run it carefully where you won't trip on it, plug in the A/C, and relax. Don't cheap out and use an extension cord with a low rating, or one you just found lying around, and you'll be fine.
posted by pocams at 3:55 PM on June 5, 2008

You know, there's an entirely different solution to this problem. It's the one I use when the weather gets blisteringly hot.

You buy a big plastic bin and a table fan. That's a one-time expense. When the weather gets hot, you go to the corner grocery store and buy two large bags of ice.

The ice goes into the bin. The table fan is set to blow air over the ice. Leave it near where you are, and enjoy the coolness of it. Total expense? Not very damned much.

Not really a good solution if you get lots of hot days per year and you need to solve the problem for a decade, but if it's only two months, or if you only get a few hot days a year, it's a good answer.

(By the way, it's unlikely that your apartment owner would be happy about you mucking with your electric wiring, even if you hire an electrician to do it.)
posted by Class Goat at 3:58 PM on June 5, 2008

Response by poster: If this were my own house I'd have zero problem rewiring the outlet or installing a new one. I've been doing stuff like that since I was about 12.

But since this is an apartment I'm not going to touch it. Plus, I can't rewire the existing outlet anyway because the heater needs to plug into it during the winter! So that means adding an outlet, which is going to be a major pain in the ass.

I suppose I could get a 12 gauge (or even 10 if I can find it), heavy duty extension cord and run it to the only other circuit I have in my apartment (hey, it's a small place!). That circuit currently has my computer (~100W according to the UPS), and two light bulbs. I'd rather not have my computer on the same circuit as the air conditioner, but it's been like that before.
posted by sbutler at 4:03 PM on June 5, 2008

Please hire an electrician or run an extension to a properly grounded 110 outlet.

You do not want to try and DIY that outlet, there is a significant difference in 15amp and 30amp power, and while it may be possible to locate a step down transformer I wouldn't want to spend the money on it.
posted by iamabot at 4:04 PM on June 5, 2008

GuyZero writes "I'm pretty sure that a 240V outlet has the proper neutral."

It's pretty rare for a three prong 220V grounded receptacle servicing a pure 220v load like base board heaters to have a neutral available. Never say never of course, especially when it comes to domestic wiring, but I haven't seen it.

You need a 12 gauge extension cord for up to about 25' if you want to go that route. Bigger will work but is unnessecary unless you are running it a longer distance. Make sure the cord does not run under anything like a rug. Even running it under furniture can be hazardous if you tend to collect stuff under your couch. You need it exposed to air to cool.

caddis writes "when did 'Related Questions' get implemented? Very cool"

Yesterday. Ya pretty cool, the first related hit is actually sort of applicable, I talk a bit about electric base board heat in it.
posted by Mitheral at 4:06 PM on June 5, 2008

I've successfully run a small (probably ~5000 BTU) air conditioner on an "outdoor" extension cord, on the same circuit as my computer and monitor, without frying anything. It helps to have a good power strip like this one that isolates the channels.
posted by cabingirl at 5:36 PM on June 5, 2008

You could break down and get a portable room AC instead of a window AC.

These can be placed several feet from the exhaust location (usually a window) and are usually 120VAC.

When I did a Lowes search for air conditioners, the 10kBTU Frigidaire unit was around $450, or roughly the same price as a portable room AC, also at Lowes.
posted by tomierna at 6:20 PM on June 5, 2008

As Mitheral said get a 12 gauge appliance extension cord and use a different circuit.

Or just plug it into the kitchen circuit but don't run the microwave and the air conditioner at the same time. The air conditioner and refrigerator together should be fine. Even the air conditioner and microwave should be fine for short periods of a few minutes or so. Circuit breakers and fuses have a time delay built into them to handle temporary overloads that are not dangerous. It takes a very long time to build up heat even in a 14 gauge circuit.
posted by JackFlash at 7:00 PM on June 5, 2008

Well, it's not code but it's legit:
Break power to the entire box
remove/replace breaker to whatever is necessary

You'll be taking off two hots, ground still goes to the neutral/ground rail

Place one of the hots on the neutral/ground rail with the rest of the neutrals/grounds.

Reconnect hot to breaker.

No need to run new wires.

Of course, your neutral may or may not be the wrong color. If it is, flag it. You might need to run a pigtail to make the old hot long enough to reach the neutral rail.

Now, go back to your outlet with your shiny new plug and remember which color is hot/neutral/ground as per your new breaker, install and close and be on your merry way.

This may or may not be code and isn't recommended if you don't know what you are doing. You can kill yourself. That being said, I would do this. Also, it might get you evicted if your landlordie finds out.

Of course, a non-grounded fridge/microwave circuit is a little...well, subpar.
posted by TomMelee at 7:29 PM on June 5, 2008

A quick google search comes up with this for proper extension cord ratings:


posted by gjc at 7:29 PM on June 5, 2008

If you know an electrician it is really quiet easy. Lets assume your two hot-legs (phase) wires are red/black. Your 220v box will probably NOT have an existing neutral, just a ground. DO NOT USE THE GROUND AS A NEUTRAL, EVER.

If done properly there is nothing wrong with changing to a 120v receptacle by "turning" or re-purposing the, say, red wire into a "neutral" but putting it on the neutral side of the new 120v receptacle and then getting a single circuit breaker (remove the 220v two phase breaker) and putting the black on the breaker and the red on the neutral bus bar (rail, whatever.) Whether the coating on the wire is red, white or pink, it's still just copper inside, what matters is where it starts and terminates. I would put some white electrical tape temporarily on the red wire just for show/identity.

Use the proper rating breaker as per AC mfg specs. I'm sure the existing baseboard heater 220v wiring is not less than 12 guage. You buy new 120v receptacle, receptacle plate, single circuit breaker, maybe white tape, done.

Then when you move out, reverse the procedure and reinstall the old 220v receptacle and breaker returning the red to it's original place (remove the white tape) as the second phase hot-leg at each end.

Of course I don't mean "you", have an electrician do it. :)
posted by Kensational at 3:02 PM on June 6, 2008

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