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07 interior fogging on all interior glass seems to be much worse than on my old 04 prius anytime the weather is cold and humid which puzzles me. If its really humid still have interior fog after 15 miles and need to keep rear window heat strips on. AC seemed fine in hot weather. This is not fixed by changing to recirculation or exterior air flow. Is this something I need to get used to or am I missing something??? [ new england CT/RI area ].
 

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Im talking with the defroster on. [never tried turning it off to solve the problem. that thought had not occurred to me.]
 

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Do you have "Auto A/C" selected and the ac compressor 'on' as shown on the soft button on the Climate screen? If you leave the compressor on all of the time, it will properly condition the air to reduce fogging. It does not mean that the compressor is running continuously. It means that it can run when needed to reduce humidity.
 

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The AC is on according to the climate panel, also front and rear defrost. Results suggest rhe AC is not running
 

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Try turning off the front defroster. When it's on you don't have auto A/C. Even in auto A/C some air flow is directed on the windshield and should keep it clear of fog. What temperature setting are you using? I find 71 or 72 to be the most effective and comfortable for me. I hardly ever need the front defroster, but do use the rear defroster occasionally.
 

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I've seen this starting on my '04 in the past few weeks, too. It seems as if my A/C compressor has died, as even making certain it is on, it still takes forever to defog. It used to defog significantly faster.
 

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firepa63 said:
Try turning off the front defroster. When it's on you don't have auto A/C. Even in auto A/C some air flow is directed on the windshield and should keep it clear of fog. What temperature setting are you using? I find 71 or 72 to be the most effective and comfortable for me. I hardly ever need the front defroster, but do use the rear defroster occasionally.
It is my understanding that the compressor does come on 100% of the time while in defrost mode. This has been true in any car that I have owned.
 

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redwein said:
It is my understanding that the compressor does come on 100% of the time while in defrost mode. This has been true in any car that I have owned.
You are correct. The point I was trying to make is that in auto A/C you will have conditioned air throughout the car. This dehumidified air should keep the windshield clear, especially since a small amount of air flow is constantly directed on the windshield. The other possibility the OP may be experiencing is low refrigerant in the system.
 

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I see what you are saying now and I agree. For defogging "all" of the windows, defrost is probably not the best choice. If they aren't using defrost then it does sound like something is wrong with the A/C compressor/system.
 

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I don't know that I'd go so far as to say that there is a problem with your compressor just because you have fogging. For example: if you have a vehicle with no A/C and put it in defrost you are running air up to the windshield to remove interior condensation. To do this effectively without the dehumidification of an A/C compressor you have to have a good volume of air moving against the fogging surface, and it should be sufficiently heated; don't ask me the temperature delta necessary to fend of condensation, but that is generally what has to occur. If you have a vehicle with no A/C and have fogged windows and the vehicle is cold, it may be a few minutes until there is enough engine heat being generated to heat the air moving over the surface of the glass to effectively remove fog.

Blowing cold, but conditioned air against a fogged glass surface will not immediately remove the fog. You have to have some sort of temperature differential in order to remove the condensation in a quick manner. The compressor helps by dehumidifying the entire cabin of the car, thus reducing the humidity in the cabin that can become condensation on the glass, thus reducing the need for a heavy volume of air flow and greater than normal heat levels. However, there has to be a change in the surface temperature of the glass to remove the condensation. This is demonstrated two ways, via heated air on the windshield and front windows of the vehicle and by the heat strips on the back window. The heat strips work regardless of air volume, or air temperature because the glass is being heated directly, but where air movement is employed, the volume of air has to be heated to accomplish the same feat.

If you do have a problem with your A/C compressor, it will show up in the summer when you want to cool the cabin and you get no cold air out of the dash registers. Until then, if you have a lot of interior condensation, increase your cabin temp, increase your fan speed direct all your air volume to the defrost output and wait with engine running, only if necessary, for the engine to start producing enough "waste" heat to provide sufficient temperature differential to do the job. Good luck!
 
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