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What's the difference between the Hot and cold defrost options?

Discussion in 'Model S' started by PhilDavid, Aug 19, 2019.

  1. PhilDavid

    PhilDavid Active Member

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    I noticed that the front windshield defrost mode has two options. When you enable it initially, it is blue, and I assume it is blowing cold air. If you long press the front windshield defrost button it turns red, and I assume blows warm air.

    I'm not sure which mode to use when. I'm a bit surprised the car does not figure out which mode to use by itself or does it based on which mode it turns on with?
     
  2. murphyS90D

    murphyS90D Member

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    If the outside air has high humidity and you use cold air defrost it will cool the windshield and condensation will form on the outside of the glass. The wipers will have to be run manually to clear it off of the glass.
     
  3. SSedan

    SSedan Active Member

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    I think the blue option is cabin temp not cold, red is full blast heating and uses much more energy.
    An ICE has so much heat energy to waste they don't give you these options.
     
  4. Saghost

    Saghost Well-Known Member

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    The Blue option directs air to the windshield vents, but continues to maintain your set cabin temperature, warmer or cooler than outside as it may be.

    Red overrides the temps, sets to "HI" and forces maximum heat onto the windshield.
     
    • Informative x 1
  5. DCEV

    DCEV Member

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    Thanks! I learned something new :)

    So basically in general the best option is the Blue Defrost option... When is it advantageous to use the Red Defrost option?
     
  6. Dithermaster

    Dithermaster Member

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    I thought it was a second press (within some time window) that made it read, not a long press? Maybe both work, but I've only used the first.
     
  7. ucmndd

    ucmndd Active Member

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    Cold temps, when you want to defrost the window as soon as possible.
     
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  8. Saghost

    Saghost Well-Known Member

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    Blue is subtle, blends in to your usage with no inconvenience and no wasted power, but might take time to achieve the desired result.

    Red has the raw power to defrost quickly when you need it, even if it overshoots your preferred cabin temps in the process.

    So Red is mostly for when you're in a hurry and didn't precondition, or for when Blue can't keep up with the severe inclement weather.
     
    • Informative x 1
  9. DCEV

    DCEV Member

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    Hmm... If that's the case I will always use the red defrost option, if I'm about to drive and use the blue defrost option if I'm parked. If I'm driving or about to drive, being able to see clearly is a matter of safety so I would want the windshield to be clear as quickly as possible with no regard to energy use.
     
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  10. PhilDavid

    PhilDavid Active Member

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    Anything else anyone want o add to the how the defrost modes should be used or is it generally use blue if not critical and red/hot air if you want the defrost to be quick?
     
  11. Hota

    Hota Member

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    In most cases you want to use the blue "defrost" - not because it saves energy but because in most cases (even in ICE) cars, you want to use the AC compressor while defrosting/defogging. Using AC removes the humidity from the air and dries off the inside of the windshield.

    Blue = Defogger = Clearing fog on inside of windshield
    Red = Defroster = Clearing frozen stuff on outside of windshield
     
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  12. PhilDavid

    PhilDavid Active Member

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    That's really helpful. Thanks!
     
  13. DCEV

    DCEV Member

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    I've heard the best way to address fob build up is to use both. Basically heat towards the windshield PLUS run the AC at the same time to remove humidity. Some high end cars do this automatically. Do we know if Tesla software can heat the windshield plus run AC at the same time?
     
  14. murphyS90D

    murphyS90D Member

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    I have run into a different situation. On a hot day, which requires air conditioning, but with very high outdoor humidity and the sun hidden by clouds condensation forms on the outside of the windshield because cold air is blowing on it. The wipers will remove it. Apparently if the eye level vents are not enabled they send the air to the windshield so enabling the eye level vents should prevent the outside condensation.
     
    • Disagree x 1
  15. Barry

    Barry Active Member

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    I believe AC is automatically turned on in defrost mode
     
  16. Saghost

    Saghost Well-Known Member

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    Pretty sure the car is running AC to dry the air that it's heating to blow on the windshield, but I'm not sure we have a way to know for certain. That's been more or less standard for defrost modes for a few decades now in nearly all cars.
     
  17. drklain

    drklain Member

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    For most cars the compressor is running for defrost mode whether it is on hot air or cold air. For those of us older folks who remember the old "slide levers" climate control systems...there were two levers. The first selected the mode - off, fan, air condition or defrost. The second selected temp -- from hot to cold. A little light would come on if AC was selected...it illuminated for both air condition and defrost modes. My kid's 2012 Ford Focus indicates the same thing (a/c light on for air condition or defrost mode selected). I suspect the Tesla does the same thing.
     
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  18. Chaserr

    Chaserr Active Member

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    When the glass is covered with ice. The app does this automatically when you precondition in frozen temperatures (you will see the defrost icon).
     
  19. DCEV

    DCEV Member

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    So it seems like the car picks the best default option automatically based on current conditions?
     
  20. Chaserr

    Chaserr Active Member

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    Maybe? There's no symbol for it in the app when it's warmer. I don't think it uses the defroster for preconditioning unless it's cold enough to freeze.
     

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