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Windshield Defogs At Record Speed (I Wish)


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Apr 17, 2002
Elk Snout, Oregon, USA
I know that I am not the only one to experience just how long it takes a cold or even warm AV to defog the windshield. ?On the last run up Mount Hood, while we played in the snow the windsheilds got dusted with snow. When it came time to leave, our windshields fogged up completely. So on comes the defrost.... and we wait.... and we wait.... After what felt like way too long of a time, only the lower 1/2 of the windshield was clear of fogging. This is with the fan and temp maxed. Once it was at 3/4's clear, we took off.

Probably, 15-20 minutes later it was 90% clear.

What gives?

Any tricks to get a faster defrost? There is no ice on the inside nor outside of the windshield - just fog.

Has anyone tried some of those wipe on anti-fogging product? Did it work?
Was the A/C compressor on when you turned on the defroster? It used to be that the compressor dried the air out, speeding things along...
Was the intake in between the rear edge of the hood and windshield free and clear??

My understanding is that this needs to be free of snow or leaves in order for the defogger/froster to work properly. If it's blocked, it pulls air in from the floor, which isn't nearly as effective...
kps said:
Was the A/C compressor on when you turned on the defroster? ?It used to be that the compressor dried the air out, speeding things along...

According to the manual.. the compressor is computer controlled and will not come on if the outside temp is too low to work correctly. so on those cold mornings when you really need it to take the humidity out of the air, as a defroster, it is basically useless. I've had the same trouble with fogged up windows and could only get the AC light to blink when trying to manually override the computers decision.. looked in manual to find that little tid bit of information thinking something else was wrong.

Has anybody used the rain-x type antifog stuff.. does it work in these type cases?
This is one of my biggest complaints with my Avalanche - and many foreign vehicles, especially Japanese built ones that seem to have weak defrosters.

I have found that if I crack open my sunroof it helps circulate the air a little better. Other than that, I've found no magic voodoo that speeds things up.

Good question to ask the GM engineers at the National Meet! >:D
actually... I thought the compressor runs automatically when the defogger/froster is put on? ? I know the light doesn't come on, but I think it's engaged regardless.

I'll pop my hood tonight and see what's happening with the compressor when in defrost...

Honestly, my defroster won't work well at all if I have snow in the front intake.. It can make a HUGE difference if that's clear or not.
I took a peek under the hood this morning when the truck was warming up. For what it's worth, it sat outside overnight, in ~ 15 to 22*F weather. The truck was starting to come up to temp when I did these tests. It was probably around 150*F.

-I set the controls to defrost. No AC light. No motion from the compressor.

I hit the AC button... it flashed. No go. The clutch is still sitting idle on the compressor.

-Set the controls to heat - no AC light. Nothing from the compressor.

Hit the AC button. Light flashed - no go. No motion from the compressor.

-Set to full COLD. No AC light. Nothing from the compressor.

Hit button... blink... nothing.



I think I'm better off just accepting it and not asking any questions. :)

I did verify that the truck takes in a huge quantity of air through the front intake with the controls set to Defrost. When it's set to that, you can hear the air getting pulled in, and as I brushed snow away I could also see it getting sucked in.
marc_w said:
Was the intake in between the rear edge of the hood and windshield free and clear?...

Great observation. It was packed with the snow off the windsheild.

I am thinking about getting on of those hair driers that plugs into the lighter. It may not be pretty but it should get me down the road faster.
Good idea...

I can never understand why automobiles dont have a defrosting element at the lower edge of the windshield, under the wipers. That'd probably melt a lot of the slush and snow from the wipers, that turns into the ice that clogs that thing up...

Another funny AC thing to note: I got out of my bowling league last night, it was probably about 25*F. I was quite hot and a little sweaty. I get in the truck, fire it up, and see the AC come on. :rolleyes: Apparently the sweat off my head was tricking the computer into thinking it was very humid in the truck.

I give up.