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I seem to have a problem with window condensation. Car was in garage overnight with a temperature of 28°F. Went for a ride and the outside air temperature was 15°F. After a short while condensation formed inside the front windshield along the top portion and also the front portions of both the driver's side window and the front passenger side window. I had the heater control on "automatic" and 75°.
I was only able to eliminate most of the condensation by cracking open the front passenger window.
How should the heater controls be set to avoid this interior condensation? Thank you.
 

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Even though it seems cold, the 28F air inside your garage held more moisture than the 15F outdoor air. As soon as the glass surfaces hit the cold outdoor air condensation happened.
You pretty much did exactly what you needed to do to rectify the situation... add heat and crack the windows a bit.

Only way to prevent it in the future would be to park the car outside vs. inside... but it's probably not worth doing that.
 

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I had the heater control on "automatic" and 75°. I was only able to eliminate most of the condensation by cracking open the front passenger window. How should the heater controls be set to avoid this interior condensation?
Where I live condensation is a pretty normal occurrence just because of the moisture in the air. Moist air contacts cold glass = condensation.

When you set the HVAC controls to a temperature that requires the car to heat the air, the car normally sends the hot air out mostly through the foot vents, because warm air rises and that gives the best distribution of heat inside the cabin. But that means the windows don't get any direct heat, so it doesn't clear any condensation from them.

The correct way to clear condensation is to use the windshield defrost button just to the right of the temperature control. This does three things:

- it turns on the air conditioner. This seems counter-intuitive, but cooling the air reduces its capacity to hold moisture and so the water in the air condenses out onto the A/C evaporator much like water forms beads on the outside of a cold glass of iced soda. The evaporator, which is inside the dash, has a special drain tube for this water that exits below the car.

- it turns on the heater. The dried air coming off the A/C evaporator is then heated, which increases its capacity to hold moisture.

- it directs the air out through the vents that stream air across the windshield and side windows. The warm, dry air then absorbs the moisture from the glass surfaces like a sponge.

It's extremely effective, and can clear even fairly heavy condensation within 15 to 30 seconds.

The rear window has no direct airflow against it, so the rear window defogger relies on heating elements to warm the glass. It's not as effective as the front defroster, but over time it will cause condensation to evaporate.
 

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I find that when the air re-circulation button is in the "on" position, condensation builds up inside. When I switch it off, the condensation vanishes rather quickly. It also helps to have the windshield defrost button on.
 

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Discussion Starter #5
Thank you for the explanations.
I will try using the maximum defrost button immediately. And I will also be certain that the air re-circulation button is not on.

As an added note I would point out that in the these temperatures (15°F) I only get 120 miles in an overnight charge. (This is with the hilltop reserve on.) I was surprised at the reduction from the advertised 240 miles.
 

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At an EV conference last fall a fellow Bolt owner recommended Rain-X interior glass Anti-Fog and it usually works quite well. In fact it is close to perfect when used on a bathroom mirror.
 

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Thank you for the explanations.
I will try using the maximum defrost button immediately. And I will also be certain that the air re-circulation button is not on.
Note that you only need to use the defrost button to clear the condensation from the window - once it's gone you can turn it off again. It may slowly reappear after a while, so use defrost as needed to clear the window. You don't want to leave it on continuously as it runs both the A/C and heater and therefore consumes quite a lot of power.
 

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Note that you only need to use the defrost button to clear the condensation from the window - once it's gone you can turn it off again. It may slowly reappear after a while, so use defrost as needed to clear the window. You don't want to leave it on continuously as it runs both the A/C and heater and therefore consumes quite a lot of power.
this morning I turned on the defrost but had AC/Heat and recirc off. all I felt was cold air. cleared the windshield. but quickly turned it off cause it was bringing in the cold outside air.
 

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this morning I turned on the defrost but had AC/Heat and recirc off. all I felt was cold air. cleared the windshield. but quickly turned it off cause it was bringing in the cold outside air.
Umm... trying to defrost with AC and Heat off is kind of defeating the purpose of it. The whole point is to cool the air to get rid of the moisture and then heat it so it can absorb all the condensation from the glass.

It'll suck a lot of juice while you use it, but you don't have to use it for long. Once you've cleared the condensation you can probably get by with Heat/AC turned off and directing outside cold air through the windshield vents so that it keeps all the moist air you exhale away from the windshield.
 

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I seem to have a problem with window condensation. Car was in garage overnight with a temperature of 28°F. Went for a ride and the outside air temperature was 15°F. After a short while condensation formed inside the front windshield along the top portion and also the front portions of both the driver's side window and the front passenger side window. I had the heater control on "automatic" and 75°.
I was only able to eliminate most of the condensation by cracking open the front passenger window.
How should the heater controls be set to avoid this interior condensation? Thank you.
You might already know this but... if it is below freezing when you take the car out and about - then there is likely snow on the ground...
Which will end up in the treads of your boots or shoes, and in your mat eventually as water.

If you can dump the pools of water out of your mats/traps after a trip - this should go a long way.
Running full defrost and or heat and A/C at same time - as others have mentioned.
"Conditioning" the Air in the summer is mostly about moisture removal from your the cabin, and that is the goal.

When I drive to work here in Canada at -10 to -20°C (last few weeks, I too crack open the passengers window to help rip the moisture out of the cabin and dry things out... with the heat cranked at my feet.) That does work well.
 

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Note that you only need to use the defrost button to clear the condensation from the window - once it's gone you can turn it off again. It may slowly reappear after a while, so use defrost as needed to clear the window. You don't want to leave it on continuously as it runs both the A/C and heater and therefore consumes quite a lot of power.
This is only true for Max Defrost, right? Not the defrost setting above the foot-well (floor) setting? I have gotten in the habit of turning on both the regular defrost and foot-well at the same time--seems to heat the car better. Am I using more battery than just the foot-well setting would use? I haven't been able to detect any difference in energy use.
 

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This is only true for Max Defrost, right? Not the defrost setting above the foot-well (floor) setting?
Yeah, the "send the air up toward the windshield" button that's over on the left side of the cluster of HVAC buttons doesn't force the A/C or heater on, it just directs the air upward. It's the one labelled "Max" that pulls out all the stops.

I should have been clearer about this - I didn't realize that that leftmost button is actually labelled "defrost" in the manual. It's not really what I'd consider to be a "defrost" button, just one of the buttons that's used to direct air one way or the other. The "Max defrost" button is the one you should use if you've got condensation on the windows that needs to be cleared.
 

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Just curious - does the compressor run at cold temps? I’m thinking this is not a heat pump version (which can tolerate ambients below freezing), so won’t run the compressor at ambient temps near freezing or below? HVAC button does say heat and a/c, implying that compressor can run at any temp, but this is probably not the case?
 

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Just curious - does the compressor run at cold temps? I’m thinking this is not a heat pump version (which can tolerate ambients below freezing), so won’t run the compressor at ambient temps near freezing or below?
That's a good question. You get frost buildup on the A/C evaporator if it gets below freezing, so I would assume that it wouldn't run at those temperatures.
 

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That's a good question. You get frost buildup on the A/C evaporator if it gets below freezing, so I would assume that it wouldn't run at those temperatures.
When you hit max defrost, doesn't it run the AC to take the moisture out of the air?
 

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When you hit max defrost, doesn't it run the AC to take the moisture out of the air?
Yes, it does. But it does that by passing the air across the cold A/C evaporator that's part of the HVAC ducting. Since cold air can't hold as much moisture as warm air, the excess moisture condenses on the evaporator coils and drips down into a drain tube.

In temperatures close to freezing moist air can form frost on the evaporator, and if it builds up thickly enough it will block the flow of air through the system. So I'd expect that the system would be designed to either shut off or curtail the A/C in those kinds of cold conditions.
 

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At an EV conference last fall a fellow Bolt owner recommended Rain-X interior glass Anti-Fog and it usually works quite well. In fact it is close to perfect when used on a bathroom mirror.
Do you find that it leaves an annoying residue? The reviews on Amazon suggest that it's a problem.
 

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We just picked up some of that rain-x anti-fog tonight, I've never tried it before but I'll let you all know how it goes.

edit: I just opened this stuff up, and it seems like basically the same thing as a kid's bubble making solution, just a light weight surfactant and isopropyl alcohol...
 

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No annoying residue if...

Do you find that it leaves an annoying residue? The reviews on Amazon suggest that it's a problem.
The trick is to keep a cloth in the car for a while and wipe any area where a problem appears. Evidently a very thin coating is a must.
 
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