Old A/C Unit - not a time to make do

The previous owners of houses leave all kinds of things when they sell a house. The house we bought is a fixer-upper and the ducting has problems in the second story. We found this lovely old window A/C unit from the early 70s??? on the balcony.

We plugged it in and to our surprise it worked, well, only one side but it was cold air. We used it for two months, but that was a mistake. Our electric bill each month was $100 dollars higher than normal. This cost us $200; it would have been better to have bought new right off the bat. Lesson learned.