What is the difference in a horizontal left hand or horizontal right hand application as far as an air handler? Also, which end would be the return and/or supply? The "a" coil is at one end and the blower motor is at the other end.
Thanks

Air handlers typically use a pull through coil design, most air handers if sold as a horizontal can lay left or right you just turn the coil over so the drain pan is on the bottom.