Recently you recommended using your AC and your defroster when defrosting the windows. The reason being the AC acts as a dehumidifier removing excess moisture from the air. This doesn’t work for two reasons. First: the small amount of moisture that cold air can hold. Example – if you heat sat…

In modern cars you have no choice. Switching the airflow to defrost, to direct it to the windshield, automatically turns on the A/C. This combination is highly effective in warm, humid weather. It may be true that A/C is of no help in cold weather but it doesn’t hurt. Some car owners have rewired t…

Also, it’s important to run the A/C a little bit year round to prevent the system from drying out-- having it automatically come on in defrost is a convenient way of forcing you to do this.

Trust me on this, at least on the cars I have owned, it works. That includes cars from 1965 though current (well maybe not current since few of any allow you not to use the A/C when defrost/fogging.)

Second: The second reason it doesn’t work is the way an AC unit removes moisture from the air. It dehumidifies by reducing the air temperature below the dew point and the excess moisture for that temperature precipitates out. If the temperature of your air is below the lowest temp your AC can cool …

In modern cars you have no choice. Switching the airflow to defrost, to direct it to the windshield, automatically turns on the A/C. Is this an American Manufacturer thing?? My 2005 4runner and wifes 2007 Lexus es-350…the AC doesn’t turn on automatically when on defrost.

One last point: the compressor WON’T run when the ambient temperature gets too low, regardless of the climate control settings.

I have successfuly used the A/C ONLY to de-fog when it was too warm to want heat. It works and thats that.

The HVAC air handler in the dash takes the cold return air through the cold evaporator to condense our the water to a dew point that is about 35-40 degree Farentheit. Then the air goes through the heater core and brought up to 80-100 degrees. The relative humidity is very low at this point so the …

I understand what the OP is trying to say, but at the end of the day its not worth trying to explain. The fact is, car manufactures have dumbed down the defrost setting so it automatically does what it needs to do to best defrost the windows.

Using your AC when defrosting your windows

Maintenance/Repairs

NYBo July 16, 2008, 2:47am 2

It dehumidifies the warm air in your car. The humidity comes mainly from your breath.

Topic		Replies	Views
Defrost/demist without AC? General Discussion hyundai , elantra	62	16151	December 26, 2012
Very cold air thru defroster General Discussion ford , escape	4	4110	August 3, 2009
Defroster Maintenance/Repairs honda , accord	8	1401	December 1, 2013
Defroster runs AC Maintenance/Repairs subaru , legacy	82	70252	July 6, 2020
Accelerate defogging and defrosting Maintenance/Repairs	6	574	June 22, 2008

Using your AC when defrosting your windows

Related topics