A/C fogs windshield

[Redd-g]

Hello to all! New member here. I have a 98 K1500. I've searched through the threads and haven't found any direct information related to WHY my A/C fogs the windshield, or HOW to remedy it. Especially on humid mornings, with the A/C running hard to cool this Louisiana hot air, the windshield will soon fog up. It'll fog up on the outside of the windshield where the defrost vents are located. Even the tiny vents on the far right and left of the dash that are pointed to the side windows will fog up the glass there. I've laid a strip of cloth across the defrost vents in an attempt to stop the A/C from blowing out there and hoped to redirect the air to my front/face vents. The air is still strong enough trough the defrost vents that it is pushing the cloth up. Air is blowing well out of the front vents. I've gotten down on the floor and observed the mode door actuator when the ignition is switched on, and while turning the mode dial on the control unit. Everything seems to be working as it should. Any ideas?

 

[RichLo]

Try some Rain-X on the windshield.

Physics say's you cant eliminate condensation but chemical engineering says you can mitigate it

 

[df2x4]

My Suburban does this too sometimes. I have noticed that it doesn't seem to happen nearly as often if the truck is clean. I have used a towel over the defrost vents before with success. Never tried Rain-X, but I will now.

Unfortunately I think this is just a side effect of normal operation, I believe the defrost vents will have some air going to them at all times.

 

[PAIRA90S]

My 90 Chevy does too. My 90 GMC only ever worked for an hour then the compressor grenaded, never got back to it. Just a big heavy belt pulley

 

[PAIRA90S]

I thought it might be a blend door issue but I see other people have the same thing.

 

[GrimsterGMC]

I had same issue, change settings to cool cab without blowing on the windscreen.

 

[JohnZ71]

Mine does the same thing on humid days. I just keep a towel up there which is underneath my dash cover so it’s not seen much.

I simply remove it when it gets to the cooler months so I can use my defrost.

I think the seals on the hvac doors have deteriorated allowing airflow to all the vents. Whenever I replace my dash, I will rebuild the hvac box and make sure everything is sealed up like it’s supposed to. I know it will make a big difference.

 

[AK49BWL]

^^ what he said, vent door deterioration, you can't stop the air from going wherever it wants anymore. All the actuation may be fine but if your rubber is gone, nothing will work.

 

[df2x4]

Whenever I replace my dash, I will rebuild the hvac box and make sure everything is sealed up like it’s supposed to. I know it will make a big difference.

I've had this done in both of my '97s at this point and I still get a little bit of air from the defrost vents if the blower is running. Red truck never causes windshield condensation, but the Suburban still does occasionally.

 

[HotWheelsBurban]

Mine does the same thing on humid days. I just keep a towel up there which is underneath my dash cover so it’s not seen much.

I simply remove it when it gets to the cooler months so I can use my defrost.

I think the seals on the hvac doors have deteriorated allowing airflow to all the vents. Whenever I replace my dash, I will rebuild the hvac box and make sure everything is sealed up like it’s supposed to. I know it will make a big difference.

Yup, Rawhide does this and I got a tan towel close to the color of the dashboard, have it up there covering the defrost vents. The time it does it the worst, is when it's very humid and you really wanna have the AC on.... So sometimes we just shut it off and drop windows. I'm sure the air box seals have shrunk; truck is 28 and most of that time it's been outside. "Garage" isn't an option for this big truck; you need a barn!