The motor in my secondary 2007 Carrier HVAC (Heat pump in attic) got damaged some time back. Got a couple of quotes for around $2k to replace it and one for around $4k. All companies mentioned that they can try to find and replace the part, but cant guarantee the rest of the HVAC will work or how long. They recommend replacing it for around $12-18k. I cant put that much money right now and am trying to a air conditioner to support the main floor HVAC. The main floor HVAC has floor vents on the top floor, but doesnt cool upper floor much. The house has vinyl sidings and possibly vinyl windows so I dont want to install window Air conditioners. Each floor is around 900 sq ft and my plan is to get a Black & Decker 12000 BTU portable AC to support the main floor HVAC. Can I get some advice for pros and cons and any alternate advice?
Portable AC advice - don't bother, don't waste your money.
Alternate advice 1:
Look into a DIY-friendly (aka "self install") mini-split rather than a portable unit (which are generally awful.)
You can get them as heat pumps, not just AC, and you can get them within the price range you're considering for the motor, rather than the price range you're unable to consider for the system. But they are a real, live system, not a flawed from the start option as every portable AC I've ever looked at seems to be.
Alternate advice 2: use fans or fans and ducts to move hot air down from the ceiling of the upper floor, or cooled air up from the floor registers to the ceiling of the second floor, or both.
Portable units are a costly, inefficient disaster of a design. I cannot dis-recommend them enough, pretty much universally. You'll go broke running them and the performance will be weak tea.
Now, the efficiency/performance issue will be resolved by using a 2-hose portable A/C. That solves the efficiency problem, by providing a dedicated supply of air - it's no longer stealing air from the room (which doesn't work very well in a modern tight house) and no longer drawing in hot, wet air from outside. However, the 2-hose portable does nothing about the cost problem.
There is nothing about a vinyl window that prohibits using a window A/C. I would look more closely at that rather than dismissing it out of hand. I once had a terrible portable A/C running in an office with a casement window 20" wide - I was able to find a 6000 BTU window A/C that narrow, and just did some light woodworking to blank the uncovered parts of the window and create a platform for the A/C to sit on. Did not need to drill into the window at all.
That said, I agree with other voices advising a "mini-split heat pump" as a better solution all around. The "Asian style" mini-splits are a huge technological leap above the clunky old American tech that dominate sales. (American makers make products that can compete, but they consider them "specialty" and charge a fortune for them, so very few people buy them). I mean look at any of the destroyed Ukrainian apartment blocks - half the apartments have a modern heat pump, and their average salary is under $5000 a year. Unfortunately the US HVAC contractor industry is sort of "rigged", and so it's hard to find contractors willing to work with the new stuff. Fortunately there are DIY options.
More on heat pumps https://www.youtube.com/watch?v=43XKfuptnik
Portable A/C units are really only suited for small spaces. I've installed plenty of them in telecom closets, server rooms, and radio/comms rooms either to supplement inadequate central cooling or for temporary purposes during outages or maintenance. I wouldn't rely on one to be able to cool an entire floor of a residence, though. They just don't have the heat transfer capacity or duty cycle of even a small split.
That said, I do own one (0.5 ton cooling) for use as an emergency backup in case we lose power during the hot part of the year, but it's more of a "we're all huddled in one room until the power comes back on" solution than something that can even dream of taking over for a failed central A/C.