You don't do a transformer. You will have 230 voltage available. It's what runs stoves and dryers. You just need a line from the panel to where you want the AC, and your expense. From a licensed electrician who knows what he's doing and can legally work on a multi family dwelling.

Or, take it back and buy something much smaller. 12,000 BTU is about the limit that 110 can run, and it had better not have any other anything on that same circuit, or you'll always be popping the breaker.

Thank you Live Wire Oak.

No, there is no 230, It's an old (prewar) NYC building. Stove operates on gas / no dryers.

Given that I cannot return / replace the unit, I do need (and would like to have recommendations / advice) a transformer.

Thanks again.

Here is a link that might be useful: The subject unit

This is a very unsuitable cooling/heating unit for your needs .
The landlord or condo property manager will likely also be quite unhappy with you when they find it.
Recommend selling it for what you can get for it and install a more suitable 120v air conditioner.

Try asking on the electrical forum. Your looking for something like a 1500w or 2kilowatt transformer. Good luck with that.

You don't want to buy some cheap Chinese crap off of Ebay that will catch on fire.

Just sell it on Ebay, and learn to read the fine print. Even if you buy a 110 unit, I'll bet your electrical service won't be able to handle it. Your building needs to do a special assessment to upgrade.

The problem is that the transformer will cut the amperage in half. A 15 amp 120v will become a 7.5 amp 240 volt.

Also, I'm not sure the transformer will handle the AC compressor start-up.

Given that I cannot return / replace the unit, I do need (and would like to have recommendations / advice) a transformer.

See link below for a transformer... which will probably weigh more than your air conditioner. BUT the question is where are you going to plug in the transformer?

No, there is no 230, It's an old (prewar) NYC building.

If you can't return the air conditioner I think you are going to have to move!

Even if you get a 120volt A/C I would be concerned that the building's wiring is adequate to power it. Do other units in your building have air conditioners?

Here is a link that might be useful: Step Up and Step Down Transformers (110Volt220Volt)

The building almost certainly has 240v wiring, but your electrical panel has only 120v circuits because they use only one of the two (or three) hot wires. The owner or building management almost certainly won't allow the electricals to be updated if you pay a flat rate for electricity rolled into your condo fees (or rent) rather than being metered separately, even if you're willing to pay for it yourself - they don't want you using more electricity that they'll have to pay for.

You're much better off buying two small 120v A/C units each off a separate circuit than trying to modify your wiring to get 240v to your A/C. Read the specs on the AC and look for ones that don't draw too many amps - Energy Star-rated units will be lower amperage for a given capacity. Watts equal amps x volts, so 5.2 amps on 240v would equate to 10.4 amps on 120v.

I have a 5000 BTU (smallest available) 120v window unit cooling a moderately-sized room and it does a surprisingly good job at keeping the room cool; only on humid 95F+ days does it have trouble coping. Having an A/C in the adjacent room helps it stay cool.