2019 Silverado - Windshield Fogging Up when Defrost is Not On

Sqrls · November 20, 2020

62 degrees is out of the designed temperature range of operation for pretty much any air conditioning. Yes, you can set it as a target temperature, but pretty much any AC is designed for achieving interior temperatures of 70-80. The reason you have condensation in the pattern that you do is actually due to lack of airflow. However, increasing airflow will actually cause more uninsulated surfaces to condensate on the exterior.
The defrost vent being slightly open is actually better for your health. If it was completely closed and running ac at 62 for extended periods of time, it would guarantee mold that’s inches thick on the inside of the vent louvre. The airflow going through it prevents this issue.
So the engineers are probably completely aware of this issue and decided to focus on reducing mold growth for 99.99% of users at the expense of convenience for 0.01% of users.

aseibel · November 20, 2020

17 hours ago, Jav_eee said:

You misunderstood.

Defrost setting is NOT activated.

There is NO WAY to pick a setting that blows air to the face AND NOT to the windshield.

so what setting is activated then?

I'm confused why you are not able to adjust your HVAC to meet both your needs and the atmospheric conditions. It sounds like you are not willing to use any setting other than MAX AC AUTO. If you get it off the auto setting, doesn't 90% of the air blow out of the vents, and only 10% (probably less) blow on the windshield? This is not suitable for you? I leave mine set at 70 degrees AUTO pretty much all the time. If its hotter than that it blows cool air. If its cooler, it blows warm. The number on the dial does not indicate the actual temperature of the air blowing out, rather it is a thermostat. so if you set the dial to 65 or 70, it still blows cold air when the ambient temp is higher. The only difference, is the auto setting forces the fan speed to ramp up when there is a greater difference between your chosen temp setting and the actual temp in the cab. I think there is a way for you to remain comfortable without full force cold air blowing on the windshield.

Jav_eee · November 20, 2020

so what setting is activated then?

I'm confused why you are not able to adjust your HVAC to meet both your needs and the atmospheric conditions. It sounds like you are not willing to use any setting other than MAX AC AUTO. If you get it off the auto setting, doesn't 90% of the air blow out of the vents, and only 10% (probably less) blow on the windshield? This is not suitable for you? I leave mine set at 70 degrees AUTO pretty much all the time. If its hotter than that it blows cool air. If its cooler, it blows warm. The number on the dial does not indicate the actual temperature of the air blowing out, rather it is a thermostat. so if you set the dial to 65 or 70, it still blows cold air when the ambient temp is higher. The only difference, is the auto setting forces the fan speed to ramp up when there is a greater difference between your chosen temp setting and the actual temp in the cab. I think there is a way for you to remain comfortable without full force cold air blowing on the windshield.

I don’t use auto. I do have it on recirc and on LO. My comfort is my preference. If your geographic area allows it and you can tolerate keeping your ac set to 70 then that’s cool. Mine doesn’t and I cannot. Again, MY preference.

It’s warm and humid and the windshield fogs up because of a dumb design.

I should also state that, under these same conditions/requirements, my F150 not F250 had this problem.

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Moend · November 24, 2020

Are all the other face vents open? Is the fan speed set to high? Are the rear vents closed?

Also, have you tried to set it on feet and face?

What I am trying to get it at is MAYBE there is too much pressure in the system and the weakest is the defrost luvers

Edited November 24, 2020 by Moend

Jav_eee · November 24, 2020

Are all the other face vents open? Is the fan speed set to high? Are the rear vents closed?

Also, have you tried to set it on feet and face?

What I am trying to get it at is MAYBE there is too much pressure in the system and the weakest is the defrost luvers

All face vents are open. Fan is not higher than half and it does it even on the lowest speed. Yes, tried all the settings to get the defrost flap to “reset” it’s position but that didn’t work.

It’s just the way they made it.

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Moend · November 24, 2020

1 hour ago, Jav_eee said:

All face vents are open. Fan is not higher than half and it does it even on the lowest speed. Yes, tried all the settings to get the defrost flap to “reset” it’s position but that didn’t work.

It’s just the way they made it.

Sent from my iPhone using Tapatalk Pro

will that stinks, I think these trucks are cheaply made. unfortunately, the mind set now is for items to be replaceable often - my gut feeling tells me the louvers are just chintzy piece of plastic that barely covers the opening and with tolerance of -/+ 20% of optimal operation.

Moend · November 24, 2020

On 11/19/2020 at 9:16 PM, Sqrls said:

The defrost vent being slightly open is actually better for your health. If it was completely closed and running ac at 62 for extended periods of time, it would guarantee mold that’s inches thick on the inside of the vent louvre. The airflow going through it prevents this issue.
So the engineers are probably completely aware of this issue and decided to focus on reducing mold growth for 99.99% of users at the expense of convenience for 0.01% of users.

Although, your theory make somewhat sense to me, i find it hard to believe that is the sole reason. also I believe the ratio you mentioned should have been %70 to %30, upward of %15 of new trucks are sold in TX according to Edmund, I lived in Houston for 8 months and brother you would be blasting that AC on a nice July morning, also been to Louisiana and they also get very humid hot summer (actually me and the wife ran AC in Feb in Louisiana - northern folks here very low tolerant to heat).

I think it is a flowed system is all, I don't think mold was in mid when the co-op was modeling the duct work.

Edited November 24, 2020 by Moend

Sqrls · November 24, 2020

4 hours ago, Moend said:

Although, your theory make somewhat sense to me, i find it hard to believe that is the sole reason. also I believe the ratio you mentioned should have been %70 to %30, upward of %15 of new trucks are sold in TX according to Edmund, I lived in Houston for 8 months and brother you would be blasting that AC on a nice July morning, also been to Louisiana and they also get very humid hot summer (actually me and the wife ran AC in Feb in Louisiana - northern folks here very low tolerant to heat).

I think it is a flowed system is all, I don't think mold was in mid when the co-op was modeling the duct work.

Preventing mold is definitely not the priority in the design, but efficient air conditioning operation and design shares a lot of the same principles. Mold prevention is definitely a design point. There are quite a few TSBs about moldy smelling A/C that GM has to deal with. If the vent was completely closed, the area under the windshield above the dashboard would be a pocket of hot humid air, especially so in hotter climates. The vent being slightly open greatly increases circulation throughout the cabin. For severe condensation to form with low air flow, the cabin air temperature will be under 70degrees. It would also take quite a bit of run time for the ac to get cold enough to form condensation on the windshield in 90+ degree temperatures. There are other reasons as well from a design standpoint, so there is justification for this design.

however, to counter the problem, the windshield would need to be insulated or heated. Otherwise opening a window would also help. Or turning off Max a/c and recirculate.

Sqrls · November 24, 2020

Also check cabin air filter. A severely restricted cabin air filter would cause this issue as well. Pretty much for the ac to get cold enough to cause this much condensation on the windshield would require the evaporator temp to be very low from insufficient load.

Edited November 24, 2020 by Sqrls