83 300 SD Lack of Floor Heat

My 83 300 is not blowing heat into the driver's footwell. There is plenty of heat in the passenger's footwell. I removed the cover under the steering
wheel to take a look. The blower works fine and when the temp. dial is moved to cold - the air blow cold out cold from the panel vents. It appears that all modes (except for the floor heat) are working.
From what I can tell - the blend door for the driver's footwell is not working. If I move it with my hand - plenty of heat. It won't stay open. Looks to be a vacuum actuator for the heat door that has fail. Can anyone verify my diagnosis and also let me know where the blend door actuator is located? My feet and I thank you!

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