Lately my 2001 GMC Yukon XL does not seem to get any fresh air because all the windows fog up. Putting A/C on or putting the button on outside air and not recirc. air along with putting on the defrost does not help. Could something be blocking a duct or something and how can you clean it out? There was a bad smell when putting on defrost about a month or so ago. Thanks
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Re: Fogging up issues
If you can feel the air from the blower motor blowing up on the windshield it is probably one of two things. Either your heater core has a leak and the anti-freeze mist film is all over the windows or your heater control valve is not working.
Does the heater get hot or can you feel hot air on the windshield? If so your heater core is probably leaking and making steam inside your car.
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I think the flapper doors which direct the air flow are all controlled by engine vacuum which is piped through a one way valve (check valve), then into a vacuum resivoir, then to dash. Any leak in vacuum will cause this issue.
If it were a leaking heater core, the inside glass surface would have an oily film along with the fog.
It sounds like your fresh air intake is not working. You have to get fresh air from the outside to be able to get rid of the excess moisture inside the cabin. Or you have excessive moisture inside from a water leak that the system can't overcome.
Windows fog up because of the humidity in the car. Run the ac and this removes the humidity from the air and the windows will not fog. If you do not have air flowing from the vents then check that the selection control is moving the vent doors . Check that the vacuum line is connected and not broken.
Could be a blend door problem. You would need fresh air from the outside to keep the windows from fogging up. If the blend door that controls outside air gets stuck or fails to open, you may not get fresh air. The ac compressor would also need to run every few minutes to dry the air hitting the windshield.
Make sure the vent system is set to draw air from outside. If it is set to recirculate the same air that's inside the vehicle without drawing fresh air from outside, the resulting humidity that builds up inside the vehicle can fog the windows even when you run the defrost. You can also try opening the windows a bit to get some more air moving inside.
If it still fogs when the vents are set properly, you may have a leaky heater core. The heater core is a small radiator that is located under the dash that the heater system blows air through to heat the inside of your car and provide heat to defrost the windshield. The fog may be coming from the heater core leaking hot coolant steam that's being circulated through the defrost system. If this is so, you will need to replace the heater core.
to clear the interior of fog you must put the fan on recirc and #3 fan position.with the a/c on HOT.it will clear as soon as any heat from the engine is allowed to the heater matrix to dry out the interior.if you allow fresh air into the car with fogged up glass,they will get worse as the temp is warmer inside the car than out.(they collect condensation).
WellI don't know a whole lot about cars but my 2001 Yukon was doing this exact thing and I took it to the shop and it was the accuator under the seat! It was fairly cheap and now it's working perfect, hope this helps..... oh it was $90.