Air Conditioning - Is it possible to use one AC unit instead of two?

My condo has two air conditioning units; one for the upstairs, one for the downstairs. They are both very old - one is slightly older than I am!

I understand that there are some tax credits available right now for effecient air conditioning systems, but these units are very small and would not qualify (so I've been told.)

I'm wondering if there is a way to use one larger unit intsead of two smaller ones. No other condo's in this community do this, but many are still using the same original units, which are about 26 years old.

If anyone can answer this, I'd be quite grateful. Likewise, if anyone happens to have a link handy for more info on the tax credit I mentioned, I'd appreciate that as well :)

Thanks

Do you room for the new ductwork? If you replace with one system, you'll want a zoned system with a variable speed blower.

Do you room for the new ductwork? If you replace with one system, you'll want a zoned system with a variable speed blower.

Is this because the new unit would be much more effective? There's not much budget here, as I don't plan to live in this condo for more than a year longer, so if I've got to replace the blowers as well, that's out of the question.

It's because with a zoned system when one zone is happy it reduces the amount of air going into that zone and the airflow has to slow down correspondingly. Frankly, if you're moving in a year, my suggestion is don't do anything unless you have a breakdown. You won't get your money back out of new units and you won't improve efficiency that much by pairing new outdoor units with the old indoor coils. Some manufacturers won't give you a warranty on the outdoor units if you don't replace at least the indoor coils. I doubt the real estate markets will improve that much in the next year however I am not a realtor or economist.

Moving in a year...
Don't do anything. Cost of a new system to combine the two, if at all feasable would be $3000 to install zoning, cost on variable furnace $1200 plus install, ??? Unknown cost on the ductwork mods, and Probably way more on the outdoor Equipment.
If it fails, replace only what breaks. Daddyjohn seems on the money.

Moving in a year...
Don't do anything. Cost of a new system to combine the two, if at all feasable would be $3000 to install zoning, cost on variable furnace $1200 plus install, ??? Unknown cost on the ductwork mods, and Probably way more on the outdoor Equipment.
If it fails, replace only what breaks. Daddyjohn seems on the money.

That's been my inclination all along, but I had to replace the outdoor fan on the old unit earlier, so it's showing signs of old age. Our last electric bill was pretty ridiculous, and both units are pretty inefficient, so the optimistic math goes something like this:

(Cost of new unit - tax credit) < (electric bill savings over the rest of the summer and next summer + perceived value when selling condo)

Add in the likelihood of either unit failing again and I started to consider my options.

Hence this thread :) Based on your responses, however, I'm thinking my equation is optimistic and incomplete :)

Thanks a lot for your input, I think I'll take my chances and hope neither unit fails me for the duration of my stay here.