I have tried many settings but on humid mornings the outside of the windshield gets so foggy...

Discussion in 'Gen 2 Prius Main Forum' started by ukiltmybrutha, Aug 19, 2021.

  1. ukiltmybrutha

    ukiltmybrutha Member

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    ....and I get stuck using the wipers for 20 minutes to stop it from fogging over.

    There seems to be no silver bullet for this and it is very dangerous when the sun's glare hits.

    Any ideas on what the perfect settings are? I have tried AC on/recirc off and defroster on to no avail.

    Thanks.
     
  2. bisco

    bisco cookie crumbler

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    i have to use the wipers too, have you tried rain x?
     
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  3. ukiltmybrutha

    ukiltmybrutha Member

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    I just applied Rain-x. Will see how that goes!
     
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  4. ChapmanF

    ChapmanF Senior Member

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    What's the typical temperature and dewpoint on these mornings?

    What temperature setting are you using with the defroster? It has to be high enough to warm the glass above the dewpoint. That might be a tall order before the engine is fully warmed up.

    There are electric heat elements built into the heater for use before the engine is warmed, but only around 700 watts worth. That's peanuts compared to the roughly 5300 watts of heat it can extract from the coolant when the engine is at operating temp.

    Worse, the electric elements are in two places, half in the heater core (so they can heat to any outlet), and half in the footwell duct (where they can't contribute in defrost mode). So until the engine gets warm, you're pretty much limited to 350 watts of heat you can aim at the glass.

    Meanwhile, the defrost mode tends to bring in the A/C as well. That's normally a good idea, to dry the air hitting the inside of the glass so it won't fog on the inside. But of course in drying the air it also cools it, working somewhat against your small amount of available heat trying to warm the glass to keep the outside surface clear.
     
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  5. sam spade 2

    sam spade 2 Senior Member

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    You are over-cooling the interior.
    It should NOT be on recirc and the temp should be set so that it just barely cools.
     
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  6. Another

    Another Active Member

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  7. bat4255

    bat4255 2017 Prius v #2 and 2008 Gen II #2

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    With higher dew points (70-75 like we have here) this is normal.
    The temp coming out of the A/C and defrost is well below that.
    Think of the sweat on a cold beverage outside in this muggy mess, same thing.
    They only way around it I know of is no A/c or defrost.
     
  8. ChapmanF

    ChapmanF Senior Member

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    I'd still be interested in what both the morning temperatures and dewpoints are where the OP is.

    The defroster activates the A/C, which cools the incoming air a bit, but it can also be reheated if the temperature setting calls for that. Trouble is, the reheating ability is limited to about 350 watts while the engine warms up.
     
  9. bat4255

    bat4255 2017 Prius v #2 and 2008 Gen II #2

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    It looks to be about low 70's if VA is where he lives.
    Hourly Graphical Forecast for 37.71N 77.54W
     
  10. ChapmanF

    ChapmanF Senior Member

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    Looks like I should have similar conditions here around 7 am, might play around and see what kind of discharge temperature I can get.

    On the optimistic side, it just has to be somewhat above 70 ℉, and it's coming in already at that temperature, and so humid that the A/C might be taking out more latent than sensible heat and so not dropping its temperature very much. It remains to be seen what the electric heat elements can boost it up to, while the engine's still cold.

    I won't be able to get directly comparable results to Gen 2 because I have a Gen 3, where the electric heating is arranged differently; it's all in one unit right above the heater core, so it can be used at full power no matter what outlet is selected. Gen 2 can only use half its electric heat power for defrost, because the other unit is located in the duct to the footwell outlets.
     
  11. ChapmanF

    ChapmanF Senior Member

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    On my Gen 3, set for defrost, A/C button off (defrost uses the A/C anyway), and temp setting the discharge temp at the defrost vent was immediately about 77 ℉ and went steadily up from there as the engine warmed ... by the time the engine coolant was 120 ℉ (which only took a minute or two) the discharge temperature was over 100 ℉. The A/C compressor was winding pretty high at that point (1650 watts), but still the heating predominated; at no point was the discharge temperature lower than ambient, and it was above the dewpoint the whole time.
     
  12. fotomoto

    fotomoto Senior Member

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    First: CLEAN, clean, clean, the glass. A dirty film on the inside surface makes the condition worse.

    Set HVAC to Auto and use HIGHER temperature settings to get the inside and outside of the windshield close(r) to the same temps. Directing cold and humid air onto the interior side of the glass makes things worse. Use wipers.

    Yet another beneficial reason for covered/garaged parking.
     
  13. sam spade 2

    sam spade 2 Senior Member

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    No it doesn't.
    He was complaining about condensation on the OUTSIDE of the glass.
     
  14. fotomoto

    fotomoto Senior Member

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    Yes, I know this.

    Just as high speeds and bald tires both contribute to dangerous handling in the rain, the condition of the inside and the outside of the windshield both contribute to the overall visibility for the driver. And YES the inside can and will create condensation (just breathe on it and you'll see it on a cool, moist day). Yes, it is a minor issue compared to exterior condensation in the OP's case but it's still a contributing factor and worth mentioning since it's so easy to rectify.
     
  15. ukiltmybrutha

    ukiltmybrutha Member

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    Thanks for educating me everyone. Issue resolved with your help.

    Will post more later.
     
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