78 450SL - How do I select Recirculate instead of Fresh Air?

[jnanasakti]

I have the owners manual on CD and the diagram shows the 'Fresh air circulating air flap' with positions of 'A - Fresh air' and 'U - circulating air' (pg 2 of the attached pdf). However, I don't have any climate control button or such to select either Circulate or Fresh air?

This is all an inquiry due to mostly cold air blowing when I turn on the heat; worked fine the last 5 years I've had this car, but somethings up - just starting to trouble shoot.

Thanks

Well, I guess I can't attached the pdf, file size is too large.