I want to Step Down my 240v wall outlet for my 115v A/C window unit. I'm not knowledgeable about electricity. Is this acceptable? From reading it seems a converter will do this job.


AC Specs enter image description here

Pic of outlet enter image description here

  • What's the nameplate amp rating (Minimum Circuit Ampacity) of your window unit? Also, what type of 240V outlet do you have? (If you're not sure, post photos and we can figure it out from there) Mar 18, 2022 at 3:22
  • In the US (where 115V, really 120V) AC window units are quite common, 240V receptacles are not so common. So you either have a situation of: previous owner had a 240V receptacle for a 240V unit or you are in a 240V country (e.g., Europe) and brought over a 120V AC from the US. If the latter, there are potentially big issues with 50 Hz. vs. 60 Hz. and maybe some other things. So clarify location and type of service (do you have 120/240 or only 240). Mar 18, 2022 at 3:39
  • Added picture of outlet and specs of AC. I live in the United States. My house is 120v in most outlets with 240v outlet shown.
    – Eric Day
    Mar 18, 2022 at 4:26
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    Is that outlet the only outlet on its circuit? Mar 18, 2022 at 11:43
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    Alternatively, get a 240v window unit A/C and enjoy the extra cooling capacity! I've seen them commonly with 25,000 BTUs!
    – Glen Yates
    Mar 18, 2022 at 17:44

2 Answers 2


There's an old joke about the company whose giant machine was not working. They had let the experienced old workers go, and hired all younger kids. No one could make the machine work. So they called one of the old workers, who now ran a consulting business. The worker came right out, inspected and listened to the machine for 10 minutes, turned one bolt, and said "There you go. Here is my invoice."

The company said "$1000!?? You turned 1 bolt! Can we have this itemized?" The old worker said "OK. $10 for turning 1 bolt. $990 for knowing which bolt to turn."

Have an electrician re-wire that for 120V

What you have here is a very simple conversion. Change the receptacle to a NEMA 5-20 type, and move 1 wire inside the service panel that supplies this circuit. It's 20 minutes of work, mostly to get familiar with the wiring so you know what to do.

But it's that kind of deal... you'd be paying mostly for mobilization (driving to your location) and the value of experience.

Still, it'll be cheaper than buying a legitimate and safe step-down transformer. They sell "cheap Chinese" step-down transformers in the $100 range on Amazon, but these are dangerous twice - first because they are junk, but second because they are not designed to step down US 240V, and will give a "hot neutral" on their output, which is bad. You would need an isolation transformer which has twice the copper, so at least twice the cost.


My suggestion is to replace the AC, assuming it is of US vintage 60Hz and you are using it in a 50Hz country. On 50Hz it will only operate at 5/6 speed reducing the output capacity of the compressor and consequently the cooling of the compressor itself. More than likely the refrigerant charge would have to be adjusted but that will not solve most of the problems.

If you are in the US have the circuit changed to 120V. This would require a breaker and an outlet change. You have the required conductors in the cable, Line, Netural, and earth ground.

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    Seeing the OP seems to be in US, would delete the top section and expand the bottom section of your answer. Breaker change might not be needed, just moving second hot to neutral bus.
    – crip659
    Mar 18, 2022 at 13:03
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    I believe the assumption in the first paragraph is wrong! The photo looks very much like it's taken in the US. It also looks quite old. If I were to assume, it would be that the outlet was installed 50 or so years ago when 240V A/Cs were more common, but today a modern 120V 15A model is adequate.
    – jay613
    Mar 18, 2022 at 20:23
  • The outlet pictures is in the US. It was installed in the early 2000's
    – Eric Day
    Mar 19, 2022 at 20:33

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