Just so you know, hot air never comes out the center vents. That is by design.

But if you have no heat from the side vents, defroster, or heater ducts, then it could be the climate control servo. That's the big plastic box in the engine bay that has vacuum, coolant, and electronic parts in it. Positioned right above the turbo. That ridiculous part is the achilles heel of the W116.

Check the routing of the heater hoses. The seller may have blocked or pinched them off for summer use.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References