Front Defrost doesn't work well, Bad Visibility, 2012 Rav4 limited - Toyota RAV4 Forums
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#1 (permalink) Old 01-02-2013, 12:04 PM
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Thumbs down Front Defrost doesn't work well, Bad Visibility, 2012 Rav4 limited

Anyone have trouble with the front defrost/defroster/defogger not working well in the 2012 Rav4 Limited? I can run mine on high for some time and it will not defog/defrost the front and/or side windows completely. Leaves a large amount of fog in the corners and top of front window and side windows stay fogged up. Results in VERY bad visibility out the front and side windows.
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#2 (permalink) Old 01-02-2013, 12:44 PM
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New cars will outgas from the plastics and other materials, and these will coat the windows and lead to easy and increased fogging. Our new cars required practically monthly cleaning of the windows for the first couple of years, until that new-car smell was gone.

That being said, our Rav clears the window just fine. As long as you don't have a lot of sopping wet things in the car, the defrost mode seems to clear everything within a few tens of seconds at most. Also, with a limited, I think you can actually run the defroster without turning on the A/C compressor, so make sure your A/C light is lit.

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#3 (permalink) Old 01-02-2013, 01:09 PM
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As metioned above, make sure your air conditioner is on when in defog mode, but also make sure that you have selected fresh instead of recirculated air. In my experience, most cars, including our Rav4, defog much more efficiently using fresh air.

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#4 (permalink) Old 01-02-2013, 02:05 PM
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Originally Posted by rav4two View Post
That being said, our Rav clears the window just fine. As long as you don't have a lot of sopping wet things in the car, the defrost mode seems to clear everything within a few tens of seconds at most. Also, with a limited, I think you can actually run the defroster without turning on the A/C compressor, so make sure your A/C light is lit.
This is incorrect. The A/C compressor is always on when in defrost mode UNLESS you have that option changed in the parameters. It can only be done using Techstream software. Just because the A/C light is out does NOT mean the compressor isn't running.

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#5 (permalink) Old 01-02-2013, 02:11 PM
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Originally Posted by JuneBug View Post
This is incorrect. The A/C compressor is always on when in defrost mode UNLESS you have that option changed in the parameters. It can only be done using Techstream software. Just because the A/C light is out does NOT mean the compressor isn't running.

However - the AC compressor will not be running if the ambient temps are near freezing or below. Since most of the Midwest is covered with a snow pack right now, I bet that is the case.

I would double-check the recirculate button, however.
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#6 (permalink) Old 01-02-2013, 04:59 PM
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However - the AC compressor will not be running if the ambient temps are near freezing or below. Since most of the Midwest is covered with a snow pack right now, I bet that is the case.

I would double-check the recirculate button, however.
There was a post/debate in here on whether the outside temperature sensor on the front bumper or if there was another sensor inside the passenger compartment airbox that is used to determine if the compressor cut-out near freezing or below.

I would speculate the inside ambient temperature reading is used because the outside temperature is always below freezing up here. If the outside ambient temperature from the front bumper sensor was used for compressor cut-out, there would be no defrosting all winter.

Maybe someone is handy with the wiring diagram to confirm the decision logic for the Defrost circuitry?

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#7 (permalink) Old 01-02-2013, 05:06 PM
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When I see other cars fogged up and mine and most others aren't I wish I had some way to pull them over and hit their Recirc Off button.

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#8 (permalink) Old 01-02-2013, 05:35 PM
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Originally Posted by CanuckRAV4 View Post
I would speculate the inside ambient temperature reading is used because the outside temperature is always below freezing up here. If the outside ambient temperature from the front bumper sensor was used for compressor cut-out, there would be no defrosting all winter.
Don't you think that heating air brought in from the cold outside will be good at defrosting/defogging? I would think so. Running the compressor when the outside air is at 2 C would probably ice up the condenser.

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#9 (permalink) Old 01-02-2013, 05:50 PM
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Originally Posted by CanuckRAV4 View Post
I would speculate the inside ambient temperature reading is used because the outside temperature is always below freezing up here. If the outside ambient temperature from the front bumper sensor was used for compressor cut-out, there would be no defrosting all winter.
The sensor is adjacent to the evaporator coil, which is behind the glove box. The sensor will shut off the compressor when evaporator temperature drops to about 4'C (39'F) approx. The reason for this is to prevent ice forming on the evaporator which would block air flow through it.

What you might find surprising is that icing can occur even on a summer day if the fan speed is set so low that the warm air is not sufficient to keep the coils warm. Since the evaporator coil is inside the vehicle, it is also possible that the evaporator temperature can be above 4'C even when outside temperature is well below that temperature.

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#10 (permalink) Old 01-02-2013, 06:10 PM
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Quote:
Originally Posted by Carbon View Post
Don't you think that heating air brought in from the cold outside will be good at defrosting/defogging? I would think so. Running the compressor when the outside air is at 2 C would probably ice up the condenser.
Heating DRY outside air will certainly works for defrosting/defogging as long as the inside humidity is low enough. Typically days with inside fogging are also those miserably cold & wet outside kind of days. Pumping more warmed air into the cabin will only increase the humidity level from evaporating melt water on the mat. If the cut-out logic dictates the compressor/condenser/evaporator stopped removing the moisture at this point, fogging can still happens with the vent in the outside air position.

My speculation/interpretation is that a sensor on the evaporator/airbox will keep the compressor/condenser working as long as the evaporator core is not in the near freezing/iced up temperature range. With the temperature selector is in the heat position you're getting a blend of heated air to moderate the ice-up effect at the core. This compressor cut-out effect can also be observed in the summer when outside temperature is definitely higher than freezing, but the evaporator core can still iced up due to localized high humidity condition. Any merits?

Edited to add RickL beats me to the post. Thanks.

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