O.K. I did a search but couldn't find anyone with my exact problem. So here goes.

I have a '88 GXL, and when I turn on the heater it blows hot air alright, but it fogs up the inside of the wind shield really bad. I tried to use it in all kinds of weather conditions and makes no difference if it's hot outside or cold. the inside of the window just fogs up.

I checked the hoses and they look alright, I'm wondering if the core is bad? Any thoughts?

 

does it do it when the air condition is on or only when off?

 

With the A/C on there is no problem. just when I use the heater. I've also noticed that the windshield fogs up on the inside if I leave the car out some where over night (like at work) and it's impossible to de-fog it from the inside. I wonder if I could use one of those products that you spray on the windshield that keep it from foging during the rain. I think its called Rain-X or something like that. But I'll still need to see whats going on with the heater.

 

When you set the Logicon setting to the window defrost position does the air indeed blow thru the vents at the windshield????? You left that part out of the question. Do any of the buttons on the logicon work? Rainex is GREAT stuff on the outside. On the inside, I don't know.

 

Are you leaving your heater on RECIRCULATE or FRESH AIR!?
make sure it isnt set to the symbol that looks like this:

___
C-->

(my crude drawing of a u-shaped arrow)

 

I don't think you understood my question.

I will re-phrase:

If the temp setting is on heat and the air conditioner and interior blower/fan is on, does the windsheild still fog up?

And although I didn't ask before, is the re-circulate on or off?

 

The temp setting is on heat. Anywhere from warm all the way to hot. I've never tried to run the heat with the A/C on, and I have tried the heater in the fresh air and re circulate mode. this seems not to change the fogging effect at all. From what I can tell the Logicon seems to be working properly it directs the air flow to the right places.

 

Not at you. At those who asked about it. "Why, yes, I drive with the heat and a/c on together all the time..."

Sounds like moisture is sitting somewhere inside your air ducting. You hit the fan, air blows past it, becomes slightly more humid and then the moisture condenses on the cool windshield when the air comes out of the defog vents. My first guess is that there is a slight leak at or near the heater core. Has your coolant level been stable? Or maybe water is getting inside through a hole or whatever and has pooled somewhere. The moisture that is humidifying the air must be coming from somewhere inside the car.

That's my big dumb theory.

ttyl,
Amur_

 

You may have a point. I was planing to replace the radiator very soon just as a precaution. It's a rather old car (1988) and the radiator is OE. So I guess I'll have the mechanic check out the heater core and the ducting. I've change the coolant and I have noticed a drop in the over flow level lately.

This sound like a reasonable theory Amur_ thanks.