Should I replce the coil with a trane compatible with the current unit instaled a year ago? What would be the difference. Finally, my house is 2000 sq ft from 1983 and the ducts are I don't think placed in right positions.

You replaced what a year ago? The furnace or the a/c unit

I replced the furnace and they left the old coil in. I was not aware of it. The new trane is not align properly either. I also would like toknow where is the blower fan speed switch maybe is on low and I would like to incrases the speed. Also the outside unit ithe old one as well a York over 10 years old.:)

As long as old coil(on top of furnace) and condenser(located outside) match, then you should be fine. You will not be able to adjust blower speed for ac, it comes set on high. You can only up the heating speed. And it won't be a switch, you would actually have to move some wires around. Now, the coil should have been cleaned when new furnace was installed. What is the actuall problem you are experiencing, or are you just wondering about ac. As far as vents go, they are usually placed on outside walls, under windows and near doors. Also usually one under vanitys in bathrooms and under kitchen sink cabinet.(these are supplys) Returns are usually located on inside walls , in hallways, etc, etc.