2002 GMC Yukon with foggy windows?

[HOGEYE]

My Yukon has not been able to adequatley defrost the windows. It seems as the vehicle cannot get rid of the moisture. I don't smell anything like I have with other vehicles when the heater core goes out (sweet smell). Could there be a plugged filter or some sort of exhaust valve or vent.Where are these located? I have also heard that the the AC compressor kicks in when the defrost is on to dehumidify the air. Is there any truth to this? Any thoughts?

[Shack]

In these temps, you have to let it warm up a very long time to get all the windows clear.

Can you feel a good flow and hot heat coming out of the defroster vents?

[HOGEYE]

Plenty of good flow and hot heat. Problem still persists after running for several hours.

[Shack]

I am not sure if your truck has one, but a clogged cabin air filter can cause this issue.

Have you noticed any stink coming out of the vents when first turned on?

[Jeremy airjer W]

Clean the windshield and make sure it is in fresh air mode and not recirculate!

[Macgyver55]

Also, your AC compressor should be running when you are on defrost. Have someone operate the switch from heat to defrost while you watch the compressor to see if it is engaging. Most vehicles do this to dehumidify the intake air so it defrosts better, and quicker.

[Scott K]

Also, your AC compressor should be running when you are on defrost. Have someone operate the switch from heat to defrost while you watch the compressor to see if it is engaging. Most vehicles do this to dehumidify the intake air so it defrosts better, and quicker.

Unsure about GM but fords a/c dont kick on when temps drop below 30 degrees. With all of the moisture from inside the vehicle with tracking snow in and out, it is almost impossible to keep the windows defrosted in these temps. Bring in your floor mats and let them dry, wash your windows with a good glass cleaner, try to avoid tracking in snow into the vehicle and this may help. The problem is everyone jumps in with snow on their boots then the heater melts the snow, then you have a lot of water, moisture in the truck when the heater is blowing, it raise the humidity, then you shut it off and it all freezes to the windows.

[HOGEYE]

We store the vehilce in the garage, so snow on the floor isn't a problem. I will check the passenger compartment airfiter tonight. Does anyone know for sure that the AC compressor is supposed to kick on even when the temp is cold? I will also check this when I get home to see if it is engaging. Thanks.

[jwhjr]

I got this out of the service manual related to the AC compressor operation -

Important

For A/C compressor operation, the ambient air temperature must be above 3°C (38°F).

So it looks like it doesn't operate when under 38°.

[Jeremy airjer W]

It should have an override or "a/c" button to manually turn on the a/c correct?

Seriously a clean windshield will help tremendously! Don't believe me? Clean the passenger side of your windshield and leave the driver side alone!

[Scott K]

I know Fords wont turn on if the temps are below 30 degrees. To prevent freeze up, and to help the compressor last longer.

[HOGEYE]

Where is the exhaust vent in the vehicle? If it is in the back, having a rear end full of plastic grocery bags may have plugged it temporarily?

[HOGEYE]

I emptied the back of the vehicle and cleaned the windows and the problem persists. I have not checked the cabin filter as there is good airflow coming out of the vents.

[Hafnutz]

Is it in the fresh air mode and not recirculate as Airjer stated? You have to allow fresh air in to get the moist stale air out.

[HOGEYE]

The fresh air mode is overiden by the defrost setting. The light just blinks and will only go on if it is set to panel or panel/floor mix.

I just took out the cabin filters and they were gray on one side so I will get new ones tommorow and put them in. I am hoping that is all it takes.

[MonsterMechanic]

Just to narrow the options a little more...Have you felt the air flow from the defrost vents? Does it appear to be blowing as much air as it does on a different setting(dash, floor)? Just looking to narrow out the possibility of a Mode Door and/or Motor being partially stuck or broken.

[HOGEYE]

Defrost airflow seems to be comparible to other settings. I will be putting in the new cabin filters shortly as I feel they should be replaced anyways.

[HOGEYE]

Cabin filters have been replaced and the problem is still there. I also noticed that it is worse when the rear heat is running. I can only get hot air from the rear air duct even when ther are set at cool. I have it set to cold on the front and passenger controls and notice no change in temp from the rear air ducts when adjusting the temp. Front controls seam to work fine.

[Hafnutz]

That being the case..I know those rear heater cores go bad from time to time and spring a small leak. Try disconnecting the rear heater hoses and plug them temporarily and see if the problem goes away. You gotta be getting tired of this! good luck.

[HOGEYE]

I think I have it fixed for now. I realized that these problems started after a recent battery replacement. I did some searching and found some people that had the same problems after battery replacement. I disconnected the neg battery cable for ten minutes (with key in start psition)to reset the computer and everything now seems to work and no more foggy windows. Warm and cool now works in rear too!

[Jeremy airjer W]

Interesting!