Windows Fogging suddenly. Moisture problem?

[sipman]

Hi,
my 07 z4mc does this odd thing. As I'm driving, all of a sudden, the hvac system starts shooting out humid air, which of course, condenses on the windows. Today, I was driving for 1 1/4 hours and suddenly, boom, humid air and fog all over the place. It was like someone just threw water on the sauna's hot rocks!
It occurred then another 4 times on the ride back.
I run the system on Auto, and the a/c symbol is illuminated automatically. The outside temp is close to freezing at the points when it first started happening. To be exact, it's at 33 degrees when it starts.

For the life of me, I cannot understand it. It's dry as a bone here in Philly, and it's been freezing for two weeks straight. I didn't drive into a lake or a river so where is this humidity suddenly coming from???

Thanks!

[VinnieAces]

I have the exact same problem when its cold outside, I thought maybe its because i hadnt cleaned my interior in a while and the moisture just built up and would show when it got cold...so i took a soft cloth towel and wiped all of my windows down on the inside but that didnt help at all

[onebluemcm]

If it goes into recirculation mode, recirculating interior air rather than adding fresh, outside air, it will fog up right now. My bet is that with it in full auto mode, it's cycling to recirc mode. I don't end up driving mine much in cold weather, but when I do, I always turn the a/c off and let it be in auto mode for everything else - have never had the fogging issue doing this.

[Shipkiller]

I don't know what the problem is, but I do not run mine in auto mode and do not have the issue.

I usually run with the temp set to 65', on a low fan setting.

On the way home today, I will put it in Auto and see what happens. I have never had it on automatic mode.

[pokeybritches]

Try running it with the A/C on with the 3-way vent selector biased towards the "up arrow." Turning the A/C on will suck moisture out of the cabin.

I've read on here that when the automatic climate control senses a failure, it will revert to a default mode where it goes to max defog/max heat. Basically, if it commands a certain vent to open and the vent fails to respond accordingly, it goes into this safe mode. One of the motors that controls a vent could be failing. Try a search for "A/C blows hot" or something to that effect.

However, the fact that it blows moisture into the cabin and causes the windshield to fog up suggests otherwise. The whole point of the "safe mode" is to revert the climate control system to a condition that's the safest - defogging the windshield. I would think if the A/C compressor was failing and spitting out moisture, it would always be doing it rather than occasionally malfunctioning. With no other leads though, I'd first start looking at that thread to determine if you have a bad motor or sticking vent in the climate control system.

[Huz-Z]

I usually contol the HVAC in my car manually.

But several times, when it has been cool and damp outside, the car fogged up suddenly, to the point where I could not see to drive! Most annoying. That was usually right after pulling out of the driveway, so the heating unit had no engine heat yet.

But - in the center of the left hand vent contol I think - there is a button with a "defrost" symbol. Press that and the car will go into some kind of super defog mode. I have found it incredibly effective at clearing the windows - in all conditions.

If your car fogs up again - try that!

[Pheonix]

The AC system can not generate moisture on it own! Can you easily wipe off the fog? Does it leave lots streak, residual? If it does, then you mind have a leaky heater core!

[ebruder]

I won't try to diagnose why this is happening, but I will give you a work around so you can see out of the windows. I live in the Cleveland area, and cold weather driving tricks abound here.

Ge a "foamy" type shaving cream and squirt a LITTLE bit on a soft towel. Rub it onto the inside of the pre-cleaned window, and then buff off excess. No more fogging for a couple of months.

EB

[schwank]

Is it bad that I instantly thought this was a computer problem when I read the title?

[sipman]

Originally Posted by Pheonix

The AC system can not generate moisture on it own! Can you easily wipe off the fog? Does it leave lots streak, residual? If it does, then you mind have a leaky heater core!

There is no sweet smell or syrup smell associated with this. I'm going to double check my coolant level. I personally think the condensation drain is clogged. Because if the car is switching to recycle mode, I can't imagine that me and my passenger are exhaling enough moisture to instantly cause so much condensation that the windows begin dripping!
I booked an appointment for Jan, so I should know for sure then.

[Bcookie50]

My 06 M windows fog up instantly in temps around 0 C or 32 F. I had a Z4 and never had this problem it is only with the M Roadster and happens consistantly at these temps.