Hello all. Can anyone help me with this? The side and back windows in my 2001 tracker keep fogging up. I don't think it is the heater core as I have no leaks, carpets are all dry, there's no antifreeze smell, my coolant levels are steady and my heat works great. But when the temperature drops my windows fog right up. Defrost only clears up the windshield and the front side windows, back side windows and rear windshield are completely fogged over. When I turn the heat back on and defrost off, the entire vehicle fills with fog. Any ideas what could be causing this and how to stop it?

 

Posted for help originally:

The side and back windows in my 2001 tracker keep fogging up. I don't think it is the heater core as I have no leaks, carpets are all dry, there's no antifreeze smell, my coolant levels are steady and my heat works great. But when the temperature drops my windows fog right up. Defrost only clears up the windshield and the front side windows, back side windows and rear windshield are completely fogged over. When I turn the heat back on and defrost off, the entire vehicle fills with fog. Any ideas what could be causing this and how to stop it?

11 min ago

For those interested: I also smelled an ammonia odor from my vents upon sudden acceleration. I had recently bought this car used with no warranty (2001 with only 85,000 miles) and was sure I had been screwed by the dealer and it was going to be a money pit!

So I did extensive research about both issues on the internet - but nothing seemed to fit exactly what I was experiencing and every answer was different re: what the causes could be. I did learn that because some vehicles are so small and airtight, to make sure to turn on your vehicle and open the vents on fresh air for a few minutes before taking off and to turn on your defrost/defog/heat along with the air conditioner. This helps dry out the vehicle (which is why condensation drips under your car while a/c is on, regardless of what temp) while getting it warm and cozy before you get in. Also found that opening the rear windows JUST A CRACK while driving helped keep the windows from fogging so much while keeping the vehicle warm. But when I hit about 70 mph, or accelerated to that speed suddenly (i.e. entering the highway)I would have the ammonia smell and rear windows would suddenly fog on rear windows. The smell only lasted for a minute or so, but the windows stayed fogged.

Here is the funny part - not being able to find any definitive answers and with the ammonia smell and fogged windows, I finally took it to my mechanic - certain that I would have to pay up to $1,000 for a repair to the heater core (though I didn't have all the signs of it failing) or the cats. Decided to bite the bullet because I didn't want to risk not being able to see on snowy and slippery roads, and be warm at the same time, with winter coming in Michigan! They found the issue. Mouse nest in my air box. It was blocking the ventilation allowing my windows to fog, and I was actually smelling mice urine through my vents. I walked out of the shop with a $107.81 bill for the parts, labor and deodorizer. No problems since. Love my tracker again!