I really have no idea on the '86 300E, but the blower on my '84 300D is under the passengers side kick panel in the drivers compartment. Cake to get to.
1984 300D Turbo - 4-speed manual conversion, mid-level resto
1983 300D - parts car
1979 300TD Auto - Parts car.
1985 300D Auto - Wrecked/Parts.
"If you don't know where you are going, any road will get you there". Lewis Carrol