Defrost on, windows fog up

[98BlackXSport]

I was wondering if anyone knows why and how to fix when I turn my defrost on the windows fog up really bad then after a few minutes it clears.

Also, don't think it is related but, when I turn my heat control from hot all the way to cold, I can hear something move. It sounds like it is having a hard time doing so as well. I also think whatever moves gets stuck when only adjusting the temperature small amounts at a time. When I need to adjust the temp I have to move it large amounts to get it to change.

What moves and can I lube it or something and how?

Thnx.

 

[Alec]

You're probably having sticking in the blend door. There are many posts on this subject, unfortunately it's not the easiest problem to fix.

As for the defrost, it depends on why the windows are fogging up. Sometimes the fog is on the inside and sometimes on the outside. Not sure exactly what fixes what, but sometimes if you blow cold instead of hot onto the windows the fog goes away.

 

[MrShorty]

I believe that the condensate you describe is caused by the A/C. I understand that, on the newer models, when the selector is in defrost, the a/c compressor kicks in to dry the incoming air. The moisture that the A/C removes from the air (and, in your climate, there's a lot of moisture in the air) then comes out with the defrost the next time you turn the defrost on. Don't see this with mine, because the A/C isn't tied to the defrost. Used to see it on an old chev that did have the defrost tied to the A/C. I would bet the "fix" would be to disconnect the A/C so it doesn't come on automatically with the defrost.

 

[Robert]

That isn't going to work. The A/C dries the air including the defrosted air. Your windows will defrost much more effectively with the A/C on that it will with it off. My Wife were out looking at new cars and several of them even menioned the "new feature" A/C linked defrost.

I guess it depends on how long before it starts to clear up the windshield. Here in Phoenix, I don't get to use my defrost very often but the few times that I do, I can immediately see a clear spot forming right above the defrost vents almost as soon as I turn it on. A leaking heater core can cause the windows to fog up but you would also smell antifreeze inside. Also, low refridgerant can also cause it. The answer is not to disconnect the A/C though.

 

[TPLYNCH]

When it is very humid/raining, and I have left the selector on defrost, when I start up the window will fog initially, then clear up after about 10 seconds when the compressor has run and is drying the air. I figure it's moisture/humidity that has built up while the truck was sitting that causes the initial fog...