Just a thought......

The key switch gets sloppy with years of use.

The spring return (after releasing from the start position) back to the "on" position sometimes doesn't align with the contacts.

Next time the blower doesn't run, try moving the key counterclockwise sightly and see if the blower ramps up speed.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles