Side and rear windows fog up

That's not unusual if you have a lot of people in the car. I will fog up because the glass is colder then the warm moist air hitting it, so the water condenses on the glass. Two ways to solve this issue. First open the windows a small amount to get rid of the warm air and introduce some cold air. OR second, set your defroster from full hot to slightly on the cool side with air circulation from the outside as well (i.e blend air as opposed to only cabin air)..

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.

I don't think its supposed to clear off snow, only fog or condensation. Try to remove the snow, and see if it will clear the fog. The wires connecting the defroster to the window should be on the side of the window, or behind a cover somewhere. Look for something like this:

OR:

I have a Toyota and they are not good at fog. go to parts store and rained makes a product fog x easy to apply you apply on the inside its about5 bucks or less it works

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.

bad heater core!!!

IN COLD WEATHER USE BI LEVEL AND TURN ON HEAT ON AC AND HEATER MODE SWITCH AND HEAT MODE THAT WILL KEEP WINDOWS FROM FOGGING UP KEEP CAR WARM ON THE INSIDE WHEN COLD OUT SIDE ALWAY CARRY PAPER TOWER OR SOME THING TO WIPE WINDOWS WHEN FOG UP MOST TIME I HAVE PROBLEM WINDOWS FOGGING UP WHEN YOU HAVE COLD RAIN OUT SIDE.IF WINDOWS FOG REALLY BAD I HAVE TO TURN MODE SWITCH TO COLD MODE AND TURN ON DEFOGGER.

Windows are fogging up because of condensation. Completely normal.

Could be either a plugged vent tube in the heater box [ it's on the lower outside of the firewall ] letting the water puddle and then evaporate when heated, or a leaking heater core. If it's the heater core, you will smell coolant inside the car and may have a wet area on the passenger's side floor.

Window fogging can be caused by a coolant leak in the heater core ( in car heater). Is there a sweet smell in the vehicle?