I live in a four bedroom house aprox sq ft is 1675. Two of the bedrooms cold air comes out from the vents cold while the bedroom on the oppisite side come out warm. The unit is up in the attic and all vents are connected to the unit. Please help!

If all vents are connected you should not be having a problem. Are all the vents open? Are all the supply air ducts coming out of the same end of the furnace or are some connected to the return air side?
Are there any dampers closed on the supply duct in the attic?

Go up in the attic and change your air filter. Then check all ducts to make sure the internal dampers are wide open that lead to the cold rooms. Make sure there is no restriction in the cold air returns as well.

Are all the ducts properly insulated?

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Originally Posted by hvac1000

If all vents are connected you should not be having a problem. Are all the vents open? Are all the supply air ducts coming out of the same end of the furnace or are some connected to the return air side?
Are there any dampers closed on the supply duct in the attic?

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All vents are connected and all vents are open. All supply ducts are coming from the same end of the furnace.