Ken,
Went out and checked my 1996 S500 Coupe...
You're reading out the blower voltage on your climate control pushbutton unit, right?
Service manual says maximum of 6 volts.
My S500 blower works great; lots of air through the vents. When I manually max out the blower fan speed, my reading is the same as yours... 4.8 volts.
Next step down is 3.2... and then down from there.
My A/C and blower work fine. I think you're OK electrically.
There are a number of pushbutton units (starting in '96) that LOOK the same, but they are not... so, you can't go by that.
If your vent flow rate is low, its probably something else. How long since you changed your main filter? or, maybe you need to replace the blower motor itself. I replaced mine recently (it started to squeek/squeel) and the flow was much improved.
Hope this helps, KenP