2019 Silverado - Windshield Fogging Up when Defrost is Not On

[Codeman00]

I’m having an issue with my 2019 Chevy Silverado RST.  I’m hot natured so many times in the summer, I have the A/C cranked down to Lo (62F).  There are times when I drive like this for 20-30 minutes or more, just depending.  This summer I noticed that on my drive to work on a really hot humid morning, my windshield would start to fog up due to cold air coming out of my defrost.  I’ve never had this happen before.  Sure enough I could feel cold air coming out of the defrost vent even though my defrost wasn’t on.  I tried to cycle the vent actuators and couldn’t fix the issue.   The only thing I can do is to turn up the A/C temp which is unacceptable, but it’s all I know to do.

 

I have since took the truck into the dealership and they noted that sometime around 2015-2017, all Silverado’s were designed to have a small amount of air coming out of the defrost.  The service guy said he didn’t believe it either until he went from vehicle to vehicle on the lot and all of the newer vehicles were the same.  

 

I’m really puzzled on this one at why this would be something that would be designed in and me being an engineer, it doesn’t sound right to me.  It’s honestly a HUGE SAFETY issue because my view is blocked when it shouldn’t be and I’m adjusting controls trying to get my view back, while driving.  Does anyone else have this issue and was it resolved?  Or are there others that have the same situation as this?

Edited November 16, 2020 by Codeman00

[Jav_eee]

My 2019 Sierra did it too and I thought there was an issue. Until it happened on my 2020 Silverado (company vehicle). Though not as bad as yours. Could be the use environment though. Mine usually fog up the passenger side.

 

I agree it sucks. I hate it. Thought about plugging it up but the climate I live in doesn’t really cause the issue often enough to push me to do it.

 

 

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[Vigilante375]

As far as I know, all vehicles still have air flowing through the system even if the A/C or heat isn't turned on.

 

This happens in the Silverado and ZL1.  And below is what I think is happening to you.

 

The thing that I hate in both of these vehicles is that if I want heat the heat to come on (with the AC button off), I'll turn it to 78....still cold air.  Turn it to 80, still cold air.....turn it to 83 and instant hot air and then turn it down to 82, instant cold air.  However they make these vehicles go off of what the temp is OUTSIDE the vehicle is stupid.  Just let me be able to set it to a certain temp and know that it'll be hot, cold or warm.

[Jav_eee]

As far as I know, all vehicles still have air flowing through the system even if the A/C or heat isn't turned on.
 
This happens in the Silverado and ZL1.  And below is what I think is happening to you.
 
The thing that I hate in both of these vehicles is that if I want heat the heat to come on (with the AC button off), I'll turn it to 78....still cold air.  Turn it to 80, still cold air.....turn it to 83 and instant hot air and then turn it down to 82, instant cold air.  However they make these vehicles go off of what the temp is OUTSIDE the vehicle is stupid.  Just let me be able to set it to a certain temp and know that it'll be hot, cold or warm.

Yes it goes through the entire system, it’s just directed via (formally vacuum) electronic doors/flaps.

The problem is the windshield defrost flap doesn’t completely seal (ELI5 explanation) and puts cold air on the glass when it’s not needed. Unlike every other manufacturer out there. It’s not necessary.

And the ambient temp sensor for the ac is, in my uneducated opinion, needed to keep the AC from freezing up when it’s being used during colder weather.


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[redwngr]

Presumably the condensation is on the outside of the glass?

[O Town Denali]

6 hours ago, redwngr said:

Presumably the condensation is on the outside of the glass?

Yes, on the outside

 

I keep a rolled up towel in my truck specifically to cover the vent .

 

It doesn't happen often but is a real pain when it does.

[Jav_eee]

Presumably the condensation is on the outside of the glass?

Presumably you’re gonna recommend using the wipers to clean it off?


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[redwngr]

No,  I was trying to figure if there was maybe a leak in the heater.

Inside sometimes occurs if here is a heater leak (or at least back in the no AC days that was sometimes a thing) or plugged drain for the condensation in the AC coil.

Outside,  means glass is below the dew point of the outside air.

 

When conditions are right, AC's have been similarly fogging windows for -- well as  long as we've had ac's.

A little flow thru the vents can prevent  inside fogging under some conditions. In the great lakes area we sometimes see vehicles, (especially ones that are fully manual heaters) running around with all the windows fogged/frosted on the inside  This is a sure sign that the operator isn't using the hvac to best advantage.  Know one of those folks that run the temp control on max, and then shut off fan when they are 'warm'?  Probably they also have trouble with fog/frost on inside.

 

 

The auto HVAC reduces, but doesn't eliminate the need for intervention under some circumstances. 

 

Running the a/c at a warmer temp will help.  If fan is on minimum, a higher fan speed will help too. 

Neither will clear the glass 'instantly', but can reduce the frequency of it happening. 

Yes, there will likely still be times when the dew point is close to the actual temperature that it will still be an issue.   

 

A space can be cooled by a small volume of really cold air.

It can also be cooled by a higher volume of less cold air.

 

 

[It's Tim]

On 11/16/2020 at 12:24 PM, Codeman00 said:

 It’s honestly a HUGE SAFETY issue 

Probably more of a safety issue driving down the road and playing with your phone.

Edited November 18, 2020 by It's Tim

[Jav_eee]

No,  I was trying to figure if there was maybe a leak in the heater.
Inside sometimes occurs if here is a heater leak (or at least back in the no AC days that was sometimes a thing) or plugged drain for the condensation in the AC coil.
Outside,  means glass is below the dew point of the outside air.
 
When conditions are right, AC's have been similarly fogging windows for -- well as  long as we've had ac's.
A little flow thru the vents can prevent  inside fogging under some conditions. In the great lakes area we sometimes see vehicles, (especially ones that are fully manual heaters) running around with all the windows fogged/frosted on the inside  This is a sure sign that the operator isn't using the hvac to best advantage.  Know one of those folks that run the temp control on max, and then shut off fan when they are 'warm'?  Probably they also have trouble with fog/frost on inside.
 
 
The auto HVAC reduces, but doesn't eliminate the need for intervention under some circumstances. 
 
Running the a/c at a warmer temp will help.  If fan is on minimum, a higher fan speed will help too. 
Neither will clear the glass 'instantly', but can reduce the frequency of it happening. 
Yes, there will likely still be times when the dew point is close to the actual temperature that it will still be an issue.   
 
A space can be cooled by a small volume of really cold air.
It can also be cooled by a higher volume of less cold air.
 
 

Yes, but the point of this post is that these trucks are designed to channel air flow to this spot regardless of whether it’s wanted or not. Not an issue for some people but it is for those who live in areas with year round high humidity.


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[Jav_eee]

Probably more of a safety issue driving down the road playing and with your phone.

Like everything else in life, that depends on the experience of the operator. ;)


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[Codeman00]

On 11/18/2020 at 12:14 AM, redwngr said:

Presumably the condensation is on the outside of the glass?

Yes.  It can be removed by windshield wipers.

[Codeman00]

On 11/18/2020 at 8:45 AM, Jav_eee said:

 

Yes, but the point of this post is that these trucks are designed to channel air flow to this spot regardless of whether it’s wanted or not. Not an issue for some people but it is for those who live in areas with year round high humidity.


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Absolutely agree.  This is the first vehicle that I've ever had problems with.  In my opinion the defrost should completely seal off.  In fact, my engineering opinion is the same.  I once worked as an mechanical design engineer for a Tier 2 Automotive HVAC supplier (we made the actuators).  I messaged by former manager who has been and automotive engineer most of his career and he said that it was odd also, that the ideal design is to shut off the air completely.  As posted above, apparently that's not how GM designs it now..

 

I shouldn't ever have to turn the temperature to where I'm uncomfortable as a work around to make the A/C work like it should and prevent a safety issue.

[aseibel]

This has happened to me in every car I've driven in the right conditions, usually when its very humid out. It happens when the vents are set to defrost, but not if they are blowing on me. It's not often enough I've ever worried about it.

 

So setting the temp to 62 (LOW) is the only comfortable way for you to drive in the morning? I want to understand the exact problem. What do you have the fan speed and vent selector set to? AUTO? Is there no way for you to find a setting that blows cool air at your face and not at the windshield? I think your solution is going to be to change one of the HVAC settings when the weather conditions dictate. Its not that unsafe to flick the windshield wipers, or turn the fan knob down. You should be able to do either without taking eyes off the road, right?

[Jav_eee]

This has happened to me in every car I've driven in the right conditions, usually when its very humid out. It happens when the vents are set to defrost, but not if they are blowing on me. It's not often enough I've ever worried about it.
 
So setting the temp to 62 (LOW) is the only comfortable way for you to drive in the morning? I want to understand the exact problem. What do you have the fan speed and vent selector set to? AUTO? Is there no way for you to find a setting that blows cool air at your face and not at the windshield? I think your solution is going to be to change one of the HVAC settings when the weather conditions dictate. Its not that unsafe to flick the windshield wipers, or turn the fan knob down. You should be able to do either without taking eyes off the road, right?

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.


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