Windows keeps fogging over

[firefighter_2000]

When it’s cold out, I have to leave my defrost on to keep the windows from fogging up. If I change to face/feet all of the windows begin fogging over within about 45-60 seconds. I’ve tried with the a/c compresssor on & off, recirculate on/off and it does it no matter what I do. Replaced the entire HVAC box about two years ago with new heater core & condenser and it only does it in cold weather. Not losing coolant anywhere either. Do I have a blend door malfunction somewhere maybe?

 

[BigPapa]

Sounds like it’s stuck on recirc.

 

[AH64ID]

If you crack a window does it clear up?

 

[Audiowriter]

I always leave a window slightly cracked to keep the fog at Bay...

 

[Ozymandias]

I always leave a window slightly cracked to keep the fog at Bay...

You shouldn't need to do that if the HVAC works as designed.

 

[brucejohnson]

When it’s cold out, I have to leave my defrost on to keep the windows from fogging up. If I change to face/feet all of the windows begin fogging over within about 45-60 seconds. I’ve tried with the a/c compresssor on & off, recirculate on/off and it does it no matter what I do. Replaced the entire HVAC box about two years ago with new heater core & condenser and it only does it in cold weather. Not losing coolant anywhere either. Do I have a blend door malfunction somewhere maybe?

This is an indication of high humidity in the cab.
I always have AC mode engaged, even if it is cold. Great dehumidifier. During cold weather the AC has a point where it is disabled due to lower temp efficiencies not benefiting operation.
A number of things can cause the fogging.
A water leak somewhere in the cab, like windshield, back window or third break light. Check around the floorboards and under the seats and floor mats.
A common issue is the HVAC moisture drain being plugged causing a pool of water in the HVAC box to "humidify" the interior. Find the drain (on firewall) and probe the drain, or use compressed air to see if you can unplug the drain.
The flowing air through the defrost ducts will help demist the interior windshield, but as soon as the flow of air is rerouted to other ducts the differential of the ambient air and windshield temperature/humidity cause condensation on the glass.
Same things happens when it is humid outside and the AC has some ducting to the windshield. Only the condensation occurs on the outside of the windshield...on with the wipers...until you get up sufficient external airflow or balance interior HVAC temperature on the windshield to prevent the condensation.

 

[firefighter_2000]

This is an indication of high humidity in the cab.
I always have AC mode engaged, even if it is cold. Great dehumidifier. During cold weather the AC has a point where it is disabled due to lower temp efficiencies not benefiting operation.
A number of things can cause the fogging.
A water leak somewhere in the cab, like windshield, back window or third break light. Check around the floorboards and under the seats and floor mats.
A common issue is the HVAC moisture drain being plugged causing a pool of water in the HVAC box to "humidify" the interior. Find the drain (on firewall) and probe the drain, or use compressed air to see if you can unplug the drain.
The flowing air through the defrost ducts will help demist the interior windshield, but as soon as the flow of air is rerouted to other ducts the differential of the ambient air and windshield temperature/humidity cause condensation on the glass.
Same things happens when it is humid outside and the AC has some ducting to the windshield. Only the condensation occurs on the outside of the windshield...on with the wipers...until you get up sufficient external airflow or balance interior HVAC temperature on the windshield to prevent the condensation.

Thanks for the info Bruce. That explanation helps. I’ll look into the HVAC drain tomorrow.

 

[brucejohnson]

Thanks for the info Bruce. That explanation helps. I’ll look into the HVAC drain tomorrow.

Also, Recirc should be OFF. Fresh air flowing through the vehicle helps a lot keeping things fresh and removes some humidity caused by bodily functions.

 

[slowmover]

https://www.napaonline.com/accessories/weathertech-window-deflector

Recommend these for a variety of reasons.
This thread one of them.

 

[firefighter_2000]

https://www.napaonline.com/accessories/weathertech-window-deflector

Recommend these for a variety of reasons.
This thread one of them.

I actually have them already.

 

[sag2]

Are you positive the compressor is turning on and you can feel warm line on high side and cold line on suction?