A/C Recirculation

Discussion in 'Interior City' started by Terry R, Aug 3, 2020.

  1. Terry R

    Terry R GS Stage1 Ragtop 1972

    1972 Buick GS 455. Has anyone modified the circulation system to get 100% recirculated air. The 72 manual states that on MAX setting and REC "The air flow is the same as in "A/C" except that no vacuum is applied to outside air port door diaphragm. The effect of this is to cause the air door to ONLY partially open thereby causing the system to draw SOME of its air supply from inside the car. This is an added cooling effect because the already cooled air from inside the car can now be recirculated and further cooled."
    I don't like "only" and "some". In Florida I need 100% recirculated air. The system cools fine sitting in the driveway but as soon as I am moving the air at the ducts gets quite warm. I figure the hot outside air (and from under the hood/hot engine) is compromising the evaporator.
    I would like to get only recirculated air into the evaporator by some how closing the out side air inlet and fully opening the recirculated air inlet.
    Has anyone tried this? Any suggestions or comments would be great.
    Thanks,
    Terry
     
  2. dynaflow

    dynaflow shiftless...

    ...dunno, maybe system unable to get enough air volume on MAX and REC without outside, or possibly evap could freeze up. I recall seeing Buicks from era blowing "snow" from ducts, they could get that cold...
     
  3. Terry R

    Terry R GS Stage1 Ragtop 1972

    Thanks John,
    I'll keep on digging.
     
  4. nekkidhillbilly

    nekkidhillbilly jeffreyrigged youtube channel owner

    odd they get warm the older systems usually got colder than new ones without recirc.
     
  5. philbquick

    philbquick Founders Club Member

    All systems bring in at least 10% fresh air in recirculate mode. This stops the driver from going to sleep on long trips due to lack of oxygen. It sound to me that your car has a vacuum problem. If the vacuum controlling the blend doors is marginal at idle, when you begin to drive and the vacuum becomes lower there wont be enough vacuum to keep the doors in their proper position, so, heated can can be mixed with the cooled air. You may just have a vacuum line off somewhere or a leaky diaphragm in one of the vacuum motors There are vacuum schematics in repair manuals.
     
  6. Terry R

    Terry R GS Stage1 Ragtop 1972

    Thanks fellas,
    Vacuum is 20 at idle and stays 15 t0 20 while driving. The air doors and actuator are working as they should.
    One possible problem is that the outside of the fiberglass evaporator box gets so hot that I cannot touch it. The lower part of the box is 1.5" from the headers. I plan to order heat shield material to see if that will help.
    I drove it with air intake in front of the windshield blocked off with wet rags. That dropped the temperature at the vents from 65 degrees to 60 degrees. Still not enough. The service manual says right outlet temperature should be 42 - 45 degrees at 90 degrees ambient temperature. I'm going to measure the Evap
    pressure which the manual says should be 29 - 32 psig at 90 degrees ambient temperature.
     
  7. nekkidhillbilly

    nekkidhillbilly jeffreyrigged youtube channel owner

    is the thing low on freon. you could wrap it with reflective stuff like dynamat.
     

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