Is there away to slow the speed of the fan blower?

Hello, this furnace does have a multi-speed blower motor. So, yes, as long as you don't already have it on the slowest speed. Per the manual, the speed can be adjusted via motor terminals. If the outdoor condensing unit is a two-stage model, a field provided Y2 wire can be connected to the motor using an electrical spade connector. The number 4 and 5 terminals on the motor are speed taps that will increase the blower speed for second stage cooling operation. Both the G and Y2 terminals will be energized at the same time during a call for second stage blower speed operation. The motor will run at the speed where the Y2 wire is connected (Fig 6B-1). You can also reference the chart on page 8 of the installation manual. If you have any further questions, please feel free to give us a call! Thank you.