Originally Posted by
sktn77a
You could use your old 3 ton in the 600 sq ft room. It would certainly cool the room but it wouldn't dehumidify it very well. Also, because it's so oversized, you would have air basting from the vents. Finally, it wouldn't be very a efficient solution. This biggest downside to your proposal, though, is that it wouldn't be cheap - the labor (half the cost of a new install, at least) would be more than you would want to spend to have a half-baked solution to your problem. I'd go with the new HP downstairs and window units until you can afford a 1.5 ton split system or a minisplit.