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I have a new to me 75 911, that has backdated heat exchanger setup (so no blower fan in engine bay).
The levers between the seats work properly, down no heat, up heat.
The levers on the dash. Red lower lever left heat at feet, right heat at windshield.
Is there a way to boost defrost heat with the blower in the trunk? When I move upper lever to the right it blows cold air even with the levers between the seats up. My understanding is the it is pulling air in from intake at the windshield and blowing that air inside, rather than the heated air from the back.
When I have the blower on and red lever to the left I get blown hot air on my feet...but it does not feel warm when to the right.
You have an issue with the defrost cables all right. Misaligned, loose or slipping connectors or missing outside sleeve clips.
With respect to getting some residual heat on the driver’s side when the red lever is off to the left, that is quite usual. It’s even mentioned in my owner’s manual and the suggestion is to turn off the side vent.
By the way, I also have the engine bay fan delete. Still lots of heat.
Hope this helps.
My controls only have 3 levers:
According to the manual upper lever controls outside air left is closed middle is open to right is fan assisted.
Middle is direction of outside air left is feet up is windshield
Lower is heat direction left is feet right is windshield
So from what have read there is no "boost" to the defrost of the windshield it is just relying on flow from the engine fan to push warm air to the windshield. Because right on the controls it says move upper levers left and lower lever right for max defrost.
To me coming from chevy corvairs which are air cooled it is just odd that the blower in the trunk is not used to help move the heated air.......