Replacing central air in 1790 Cape

I currently have a Ruud 3 ton that the compressor is shot. I am getting quotes anywhere from $5,400 to $10,000. My house is approximately 2000 square feet. Prior to the old air conditioning system breaking it barely kept the downstairs cool and did nothing for the upstairs although I have a total of 5 vents upstairs.
My biggest question is I have no return in the upstairs of the house and I have been told by two contractors that I DO NOT need one and three have told me that I DO.
What say you??
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the laws of physics says hot air rises. ask the morons who say you dont need a return air on the second floor just how in the hell is the hot air supposed to get back to the ac cooling coils?
let me guess their response......the cold air will eventually displace all the hot air on the second floor.......yeah, maybe when hell freezes over........
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snipped-for-privacy@gonefishin.net wrote:

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You are right that is exactly what one person said and the other said that the return that I have down stairs will take the hot from upstairs if I make it bigger. Duh!!
Thanks!
snipped-for-privacy@gonefishin.net wrote:

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I hate to be picky, but it's the cooler air that falls. This causes the warmer air to be displaced up.
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"B-Hate-Me" wrote:

whatever floats your boat!
ya think the heated air coming from ground zero in Death Valley is cooler than the air above it?
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Oh damn! That one left a mark!
Everyone knows that the heavier cooler air is held up higher in the atmosphere because of centrifugal force generated by the rotation of the earth.
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