Windows fogg up even with the defrost on

It's most likely your heater core that is causing the problem it could be leaking either from the core it's self causing anti freeze to get into your vents or from one of the hoses leading to it.....I am assuming that when your heat is on there is a dampness in the air this is what is causing the windows to fog up.

Heater radiator leak.It is under the windscreen and can blow hot water (vapor) to the glass.Does it slightly smells heated water?Very rare:rain water in the saim compartment as the heater having the same simptoms.Track the problem,ceck coolant level regularly.Cheers,hope u deal it,let others know.

This may be due to a bad heater core or dirty core with a plugged water drain, first see if the a/c works. turn it on and see if the air gets cold and if the ac compressor works.

The way the defrost works to keep windows from fogging up is that when the front defroster is tuned on the ac should also be on, on most cars when you go to defrost it will turn ac on automatic. the system then uses hot and cold air to remove the moisture in the air to avoid window fogging. if your a/c is not working then that may cause window to fog, but if you are also getting a smell then the drain that lets out condensation may be plugged and then water builds up and also mold from always being wet and when heat is on you smell that.


i want you to run the defrost and when windows fog up wipe window with hand and see if it is greasy . if it feels oily then you may have a bad heater core, the core leaks coolant out and steam and causing windows to fog up with a flim of grease.

This can be caused by a stuck blend door or a clogged heater core. Can you hear the blend door moving when you turn the temp knob? If not, it may have disconnected from the control panel or blend door. If the door works, remove the heater core and flush it or replace it.

heater core may be leaking if fogging windows or flapper door closed

Lights would not be related but the fog is caused by dirty pollen filter, if you do not want to get an expensive resistor than it is easier to change much cheaper filter.

more than likely you have a bad heater core

If the fog is slippery and not water vapor you may have a pin hole in your heater core. Try adding a stop leak to seal the heater core leak. If not, try pushing the AC button. On most foreign cars the AC compressor does not stay on long enough on defrost to clear the windows.

Your windshelid fogs up because of the cold air outside mixing with the warm air inside your car, causing the water vapor in the air to stick to your windsheild. Just turn down the heat a bit to solve the problem.

hope it works

On most vehicles the AC comes on when the defrost is on to keep AC compressor/clutch from seizing up from non use during winter months.