Defrost not working

Steven Mechanic Spokane, Washington Posted   Latest   Edited  
Case Study
HVAC
2011 Volkswagen Tiguan S 2.0L (CCTA) 6-spd (09M)—WVGBV7AX6BW522190
Windows Fogging Up
No Fault Codes

Customer complaint is that the windows fog up even though the heater is set to defrost.

I go out to get the vehicle and notice the windows are indeed foggy, and the HVAC is set to defrost. I bring the car in and scan the HVAC for faults and there are none. Next, I take a look at the HVAC data and all the temp sensors are reading correctly, and the air is plenty hot coming out of the defrost. The HVAC flap actuator data for all the HVAC doors matches desired/actual when selecting different settings with the knobs and switches. I go into Basic Settings with the scan tool and run the "Learn flap end stops", and I can hear the door flaps moving inside the dash, and the scan tool shows "Finished successfully" when it's done. Recheck if any faults set while running that procedure, and no faults stored. 

The windows have mostly cleared up now from being in the warm shop and having the vehicle doors open. I decide it's time for a road test to see if these windows are going to fog up, because everything is checking out fine so far. So, I head out onto the road and it only takes about 3 minutes before the windows are really starting to fog up. The defrost is already on, so I crank the fan up to high, but it doesn't help much. 

That's it for now. I'll update tomorrow. In the meantime, if anyone wants to comment, you are welcome to.

Update:

Everyone's replies were on the same track as I was. I checked all those things that were suggested. Rick Kearns was on the correct path to check the fresh air/recirc. flap to see if it was acutally changing positions. I took the glove box out and the acutator and flap door were right there. I ran the Learn flap end stops Basic Setting again, and the fresh air door did not move, but I could see the actuator squirming around like it was doing something, even after the procedure was done it just kept squirming. Took it out and the gear/lever was broken

Installed a new actuator and gear. The gear comes in a "lever kit" #1K0 898 002C with all of the other levers as well. So, I go ahead with the Learn flap end stops again, but it doesn't move. Why does the new one not move during the learn procedure, and why did the HVAC module not ever set a fault code for that flap? Hmm.........

My first suspicion is that the module must not monitor that one. But why would someone design a system that leaves one flap not monitored? I've never heard of that before. Lets do some researching. How are these actuators normally monitored? Position sensors, or maybe amp draw. Ok, lets go to the wiring diagram

Ah, ha! The recirc actuator does not have a position sensor, but the others do. Looks like it may not be monitored after all. So, when there is a failure, there is no fault code, just a foggy window if it is stuck on recirc. Also, the module doesn't run that actuator during the Learn process, because apparently it isn't monitored.

Thanks for reading.

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Tyler Technician
Hammonds Plains , Nova Scotia
Tyler Default
 

Is the Ac compressor running? Did you check refrigerant pressures? Also are any of the carpets really wet under the floor mats? May have a water leak aswell.

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Steven Mechanic
Spokane, Washington
Steven Default
 

Very good ideas. When I was checking the HVAC data, the refrigerant pressure checked okay when comparing to a temperature/pressure chart for R134a. We do have snow right now and the vehicle owners have kids, and I noticed all of the carpets a little wet, but not really wet. I did not check underneath the carpets. I didn't want to go that direction yet, but I kept it in mind at the time.

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Steven Mechanic
Spokane, Washington
Steven Default
 

Also, in reply to wether the AC compressor was running. On my road test I had the switch for it turned on and I watched the scan tool data to see if it was coming on. It never did come on during the whole road test. I know if the weather is too cold it won't come on. So, I decided not to go that route yet.

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Ray Diagnostician
North York, Ontario
Ray Default
 

The heater core might be leaking.

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Steven Mechanic
Spokane, Washington
Steven Default
 

Another good suggestion. Recently I purchased a car for my daughter that would fog the windows after a short drive. There was no smell of coolant and the vapor on the windows didn't feel like or smell like coolant. And the windows would clear up with the windows open. That car did have a heater core leak just slightly, but I was surprised it didn't smell or feel like coolant. I was really

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Steven: Another one I would add is clogged drain allowing condensation (water) slosh. HTH, Guido

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Steven Mechanic
Spokane, Washington
Steven Default
 

That is another good thing to check. I removed the cabin filter, which is under the glove box, to look for water. The filter was dry and no signs of water inside the case, and no signs of water overflowing onto the carpets from a clogged HVAC drain.

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Rick Technical Support Specialist
Saint Charles, Missouri
Rick Default
 

If have ruled out drain clog, heater core leak and excessive wet interior. I would make sure the outside fresh air door is open and not set for recirculating air. You wouldn’t think that would cause fogging but it does.

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Steven Mechanic
Spokane, Washington
Steven Default
 

Good thinking Rick. What do you think about there not being any faults for the air doors, and the Learn Flap End Stops runs successfully without any faults set?

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Steven Mechanic
Spokane, Washington
Steven Default
 

I've updated my original post with the fix. Thanks for the replies.

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Rick Technical Support Specialist
Saint Charles, Missouri
Rick Default
 

Steven, Great work and research. I had a recirc/fresh air door kick my but. Only once though LOL

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Jimmy Analyst
Québec, Quebec
Jimmy Default
 

Would love to include this as a case study reference in an upcoming textbook for author Jim Halderman, who I'm doing case study research for. Would you be agreeable to that? We'd love to use this and the photos. Would give you a mention in the book for it. Let me know. Either comment here or email me at …

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Steven Mechanic
Spokane, Washington
Steven Default
 

You have my permission to use this case study.

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