Windshield inside Frost

First, make sure than any moisture stored inside the car -- damp clothing or towels, boots, floor mats or carpet, is removed. Remove every wet unattached item from the car to be dried out elsewhere (wet carpets are tougher to fix). Don't be like the folks who towel off the inside windows, then leave the wet towel inside the cabin to re-evaporate and re-freeze on the glass.

This fixes only some cases, not all of them. Unfortunately, merely breathing inside the cabin releases significant moisture there, this is simply a fact of biology (exhaled air is close to 100% relative humidity at body temperature). Some drivers leave a window or two cracked slightly at night to help let this moisture out.

If you have already done all this, then we'll need to consider more ideas.

 

Like "Stop breathing" ??

In some conditions it is almost impossible to completely prevent inside frost from happening.
If it happens infrequently, I wouldn't worry about it.......beyond what you have already mentioned.

 

It used to happen to me up north in really cold weather. Didn't matter what car I was driving. The only cure was to try to vent out the humidity as much as possible and mainly to get the windshield warmer. However, there were a couple times when it was so cold that the engine thermostat wouldn't even open. Not fun!

 

The AC should be set to ON when defrosting the windshield (yes, even during winter!) so as to ensure the air is DRY. It can make a huge difference in effectiveness. Recirculate should be deselected.

FWIW, I've always thought it's not a bad idea to occasionally turn on the AC during winter anyway, so as to circulate the lubricant (in the Freon) to the compressor and other components.

 

Temperature needs to be at high all winter not 76

 

Are you saying, using Front Window Defroster (or as Toyota calls it Windshield Defogger) does not get rid of the frost? If it is the first thing in the morning and temperature is extremely low (below 10F), it will take at lest a few minutes for the engine to warm up enough to start melting the ice. But once defrosted, I can usually keep the the climate control setting manually to blow warm air to the windshield to prevent re-frosting or fogging.

Have you measured inside cabin humidity using a hygrometer? I have a small thermometer/hygrometer with min/max memory sitting on my front console. I try to keep the inside cabin humidity below 40% all the time. If it gets above that, use A/C to dehumidify. Our ambient humidity is almost always higher than 40%, so opening a window does not dry the cabin air. However, keeping the window cracked a bit will help prevent fogging up the window also.

 

I'm confused... but I know either one works.
But which method do you think is more effective?

 

The AC is set to ON with the temperature set to HIGH (or warm) so as to allow hot/warm DRY air to blast the windshield. The AC dries the air, even when set to higher temperatures (although many usually think of it only as a cooling device). Humid air + cold surface = frost!

 

AC is turn on automatically when you press Windshield Defogger button. Since it turns on the gas engine and uses the heat from it, it will take longer to warm-up than simply using the heat-pump or using external windshield warmer. I don't really know what the windshield warmer is like, but I imagine it must be electric heater. My guess is the heater will work quicker to melt the ice, but it will not get rid of the moisture it just created, so you will need have the A/C on to dehumidify. A/C at low temperature is not working to cool the air, but drying air by removing moisture.

 

I thought that in most modern cars, the AC is automatically used as part of the defrost / defog operation. My 1986 Accord didn't do this, so AC had be to applied manually, but my 1997 Legacy and everything since did so automatically.

A downside is that some of that extracted moisture pools up in the AC portion of the climate control, becoming a source of moisture to freeze again on the glass overnight. In that Honda, I made sure to turn off the AC well before the car would be parked, giving some time for this pooled moisture to evaporate and be flushed out. In newer cars, this means turning to non-defrost vent positions, if it can be done without soon suffering fog-over, not always possible.

Additional measures include making sure the fresh-vs-recirc vents remain set in the outside air position when parked, allowing more moisture to escape. Some folks with greater problems bring in a large container of desiccant (Dri-Z-Air and others) to absorb excess moisture, though these need to be changed or baked frequently.

I'm not a fan of leaving the cabin temperature set high (max, 76+ degrees, etc.). Higher temperatures allow the air to hold more moisture, thus retaining more when the car is parked. So I dial the temperature down after the initial window clearing.

Different people, different cars, very different and quite variable weather conditions, so there should be additional approaches there work for at least some folks ...

 

Not very intuitive.... but will try that next time.
I always set the temp to the lowest when using AC here in CA...
Thanks!

 

Since you live in CA, you will never need to turn the temp up to just defog. Here we are talking about defrosting ice formed inside of window at temperature well below 32F. In my neck of woods, I use defroster to melt thick ice formed outside of the windshield when temperature dips down to ~10F or lower. That said, I never had to change my temperature setting from 70F to defrost any ice on windshield.

 

In the conditions that you have, it makes NO difference.......because the A/C will not actually run when it is that cold.

AND....you don't need any additional drying anyway.

If the ambient air temp has been below 32F for more than a couple of hours, then the air contains very little moisture already. Heat up that air by 40 degrees or so and it's relative humidity approaches ZERO.

 

It snowed off the inside of my windshield once. When I started the defroster to blow it around, it was a regular Interior Wizard-Blizzard.



That's all on the inside. White specks on the dash are snow.

 

Almost everybody who lives in a climate where it occasionally gets VERY cold has that same problem.......and there really is no GOOD "fix".
Second time saying that. I quit.

 

I entirely agree with you. I live in Montreal where the night temperature easily reaches -15 °C (5 °F) and morning frosting on the interior of all glass surfaces is a common phenomenon to deal with. As long as there is snow outside (which is the case for 4-5 months of the year), there will be water pooling on the mats (which evaporates thanks to the heat left in the cabin when it is parked) and therefore frost on the windows. Even if the ice layer is quite thin, it is increadibly difficult to scratch (the handheld ice scraper which is effective on the outside windshield is completely useless on the inside due to the opposite curvature of the glass pane). Scratching pads don't work either because they require a lot of pressure on the surface. I use a stick with a swiveling pad on its end where I pour some isopropanol (rubbing alcohol, the liquid in the bottle will not freeze inside the car). This dissolves the ice and I can get going quite rapidly. If you are going to do this, be careful: you are better off by keeping the fan off until the ICE has warmed up and can generate some warm air for the cabine. If you blow cold air on the windshield, the isopopanol evaporates and leaves water on the cold surface where it freezes once again affecting visibility (sometimes I have to touch up the windshield as I drive...). And then, there is the odor of isopropanol in the cabin..., but it does not bother me.