My vents seem to have gotten stuck in the defrost position. When I looked at the center vent actuator you could see that it was trying to pull the actuator arm in but was not having any success. I pulled the actuator unit, put vacuum to both ports and you could see it trying to pull the actuator arm in but with no luck. This looks to be bad. Is this a correct assumption? Can these be fixed or should it be replaced?

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1976 300D 70K

Sounds like it. They have a rubber diaphragm in them that can tear. You can either buy a new one or order a repair kit from this site.

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Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo