Forum Discussion

flapbreaker's avatar
flapbreaker
Explorer
Aug 13, 2013

dash air won't go to defrost.

I seem to have the opposite problem that most people have when they have dash vent issue's. Instead of having defrost all the time I cannot get mine to go to defrost. I found the actuator that controls the defroster door and noticed that it didn't move when changing the dial from defrost to other settings. The arm on the actuator was in the retracted position so I pushed in the extended position with very little effort. Long story short, the actuator will retract it's arm without issues but needs a bit of assistance to extend it. Is this just a bad actuator? I assume that it uses vacuum to retract, not to extend as extending the arm puts air to the defrost and this would be the default position with no vacuum. I have the E53 chassis with v10 engine.
Class A
  • stuplich's avatar
    stuplich
    Explorer
    Aug 16, 2013
    Not "All vehicles automatically turn on the A/C when defrost has been chosen"!

    My dash A/C only turns ON when the A/C button is pushed in.
    To avoid confusion, when you "think" something is true you should preface your statement with "I am guessing", "I believe" or "I think".
    Mel
    '96 Safari
  • flapbreaker's avatar
    flapbreaker
    Explorer
    Aug 15, 2013
    Just to clarify, this issue is not specific to A/C. The problem is that I cannot get the airflow to go to the window (defrost) vents with the selector switch. The only way I can do it is if I manually push the vacuum pumps arm to the extended position. The vacuum arm will move back just fine when I put the selector to another position such as the feet. I think the broken/weakend internal spring is the correct problem. When I did a internet search trying to diagnose my issue, one consistent complaint was that most people seemed to have trouble with only getting air to the window vents. That issue is from a loss of vacuum which does default to air blowing on the windshield.
  • randallb's avatar
    randallb
    Explorer
    Aug 15, 2013
    All vehicles automatically turn on the A/C when defrost has been chosen. This application first showed up in the early 80's on most European cars. The reason for having the A/C cycle on when defrost is chosen is simple; you want to remove the moisture from the air before it hits the windshield and eventually remove as much moisture as possible. All A/Cs, building or automotive, are dehumidifiers.
    Randy
  • Argosy24's avatar
    Argosy24
    Explorer
    Aug 15, 2013
    if he's in heat it should go to defrost, it's generally default in case of failure and why people complain of only that function.

    But if he's trying to use defrost with AC (could be my mistake as I assumed due to the time of year) it's often blocked because the windshield will fog over leading to the inevitable lawsuit.

    It might not be part of the question but important because there are two different reasons it is happening, or not. There is no sense in changing the motor if the controls won't change to defrost in AC.
  • 2ndhom's avatar
    2ndhom
    Explorer
    Aug 15, 2013
    Argosy24 wrote:
    Is it supposed to go to defrost? Cold air on the windshield on a humid day could be a recipe for disaster.

    :h
    A good question ... I'll have to test mine next time I have the coach running. BUT, don't think that was part of the OP's question. I assummed (and we know where that gets us) he was in the air/heat mode.
  • Argosy24's avatar
    Argosy24
    Explorer
    Aug 14, 2013
    Is it supposed to go to defrost? Cold air on the windshield on a humid day could be a recipe for disaster.
  • flapbreaker's avatar
    flapbreaker
    Explorer
    Aug 13, 2013
    Thanks for that explanation. Makes perfect sense. I didn't know what was inside these little guys. I might try the rubber band idea before I attempt to change it out. It's in a tight spot.
  • wa8yxm's avatar
    wa8yxm
    Explorer III
    Aug 13, 2013
    Broken spring.. Inside the vacuum motor (What the device is called) is a diaphrham and a spring.. If vacuum is applied it pulls in against the spring, if vacuum is not applied the spring pushes out (Default position).

    If spring breaks, no push

    A temp repair may be as simple as using a rubber band to "pull" the thing back out.. Or an external spring.

    however I'd be worried about the internal spring possibly puncturing the diaphraham where it's broken (not likely but could happen)

    NOTE: if this happens, you can simply pull and plug the vacuum hose till you get a new vacuum motor and keep it in Defrost.
  • flapbreaker's avatar
    flapbreaker
    Explorer
    Aug 13, 2013
    Yes, I can get to the controller. Nothing seems wrong with the tubing. From what I've read, if it was a vacuum issue, by default, I should only get defrost. In my case, I cannot get defrost because the actuator needs a little assistance to extend it's arm.
  • 2ndhom's avatar
    2ndhom
    Explorer
    Aug 13, 2013
    Sounds like a loose or cracked tube ... the one that controls the defroster. Can you get to the knob controller? Not familiar with your rig but most all are controled by a tube.

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