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HVAC I (manual controls) - How's it supposed to work?

5K views 7 replies 3 participants last post by  rowdie 
#1 ·
As I was out driving in the cold last night on my longest drive yet in my 1973 450 SL, (40 miles pure highway to test mpg) I realized that I couldn't get any heat whatsoever out of the center dash vents. It appear to me that they are supposed to work that way, fresh air only. I really hope that they will provide ice cold air when running the AC in summer time. My manual appears to say that all vents will get cold AC air, especially when looking at the beginning of the last page of my owners manual. "Rapid Cooling".


I thought these pictures of my manual would be helpful for future readers and anyone who wants to confirm that my HVACI system appear to be working properly.
 

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#2 ·
BTW: My car does not have the knob on the right side of the climate control panel that is shown in the pictures above. I'd wondered what that was for a while, but have figured out that it's the Cruise Control, which my car does not have. That knob is not numbered in that diagrams/pictures above. It can obviously be ignored for the purposes of this post.
 
#4 ·
No. I don't believe that is in my manual. I'm not sure if my manual is original to my car, but IMO it matches my car better than the pictures in your photo (which shows no AC knob).

Since I know how the center vents operate in winter time with heat, I wasn't too concerned with the heating controls. I did however find your diagram/picture and save a copy though, as I've never seen anything else as descriptive that. It is VERY helpful, and in EGv107 for good reason.

So I thought I'd attempt to answer my own questions of:
- Is my HVAC operating correctly?
- Will Cold AC air come out of those center vents in the summer time (if heat doesn't come out in winter)?

I wasn't able to find those answers in EGv107. So I created this post, hoping to contribute in a positive way.

If I'm making any bad assumptions, I assume you'll let me know. :)
 
#7 ·
I once went to an MBCA meet where there were several other early cars with the manual climate controls. It happened to be a humid summer day with a strong threat of rain. As a result all cars arrived with either hard top on or rag top up.

One guy asked about the climate controls. Turns out not one of us really knew how levers should be set to provide summer defogging. I still don't know - just do it my trial and error :(

What someone should produce, is a small card similar to the pic in the above posts that could be attached to the sun-visor or elsewhere. Controls are not intuitive and looking up instructions in manual takes too long.
 
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