HVAC issue

Discussion in 'Interior City' started by 72skylarkconvt, May 11, 2021.

  1. 72skylarkconvt

    72skylarkconvt Well-Known Member

    72 with AC (which is removed). Seems that my selections for heater/vents/defrost don't work right.
    If I put it on heater I am getting about 70% out the defrost, 30 % out of heater. If I change it to vent it all comes out the vents. If I pick defrost all air pushes out the defrost. Only when I select I choose heater I don't get only air out the heater.
     
  2. 12lives

    12lives Control the controllable, let the rest go

    Sounds like one of your cable tabs has snapped off. Have you inspected the cables?
     
  3. 72skylarkconvt

    72skylarkconvt Well-Known Member

    Cable tabs?
     
  4. 12lives

    12lives Control the controllable, let the rest go

    The cable sheath has plastic tabs at each end to anchor it. If one breaks off the cable gets sloppy and the doors don't travel the full distance.
    [​IMG]
     
  5. 72skylarkconvt

    72skylarkconvt Well-Known Member

    So when I use the selector which must be electric, it is sending a signal to those cables telling which one to do what?
     
  6. 72skylarkconvt

    72skylarkconvt Well-Known Member

    Is it known which color tab controls what for 1972?
     
  7. 72skylarkconvt

    72skylarkconvt Well-Known Member

  8. 12lives

    12lives Control the controllable, let the rest go

    The lever for temp/vents are connected directly to the cable. There is a vacuum switch for some of the doors. You could have a broken hose too. You should get a manual for your car and read through the HVAC section. Picture is an example - not an AC unit.
    [​IMG]
     
    Last edited: May 18, 2021
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    That's a vacuum problem. There are several vacuum actuated doors in the system. Could be a leaky hose as well. Look in the Chassis manual in the heater/A/C section. There is also a vacuum storage container on the firewall the stores vacuum for the controls. Make sure the hose to that is leak free.
     
    12lives likes this.
  10. Rich Skylark

    Rich Skylark Gold Level Contributor

    Had a similar problem on my 68 . The cable with the blue tabs binds up usually by the HVAC controls snapping the tab off . This one controls the blend door that directs the airflow to either heat or defrost. The vacuum lines as stated are also usually at fault - cracked or fallen off after many years. If you have a service manual ,there is a vacuum hose routing diagram. There are 2 I believe that go into the engine compartment and 5 that connect under the dash . They should be color coded if original . On mine , I had the first letter of each color stamped on the vacuum connector- should be white , on the back of the HVAC controls PITA to get to if your a big guy , hope this helps.
     
    12lives likes this.

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