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Discussion Starter #1
My 2008 Passat (FSI 2.0T) has gone intermittent on the heat for no reason. Blower motor works just fine. Temp on full heat and I get cold air coming through. Then for no reason, I'm driving along and the heat works again and then off again (mostly off). I have a big trip through the mountains of Montana tomorrow and need to get my heat working again. I do not have the climate control version, just the manual climatic version. I know these can clog up in the heater cores -- but before I go through that whole mess... is there anything else than can fail on these? An actuator? A valve? the heater knob itself? Thanks.
 

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Blend door actuator probably. Heater cores are a big problem in the B5 Passat but in the B6 they don't clog up any more than the average car. You'll have to suffer through this trip though unless you want to take apart most of the dash tonight.
 

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Discussion Starter #3
Blend door actuator probably. Heater cores are a big problem in the B5 Passat but in the B6 they don't clog up any more than the average car. You'll have to suffer through this trip though unless you want to take apart most of the dash tonight.
Aaargh! Serious!? Which blend door do you think? And the entire dash has to come out to replace it?
 

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Discussion Starter #4 (Edited)
Aaargh! Serious!? Which blend door do you think? And the entire dash has to come out to replace it?
Going to flush the heater core first and hope that fixes it. The more I think about it... gotta be the heater core. Must remember to bleed the air out of the core when I am finished (many forget). Going to use the CLR + auxiliary pump + compressed air as final step to get this thing clear of all the crud. Does anyone know what diameter (ID) hose is used going into the heater core? One big clue that it is the heater core is that it likes to act up when idling and then clear its through on the interstate. Almost a dead giveaway. If this was the climatronic version... then I would wonder about things like temp sensors and fancy flaps... but I am almost positive this is the heater core the more I think about it. Wish me luck. I will let you know of the final result. Stay tuned...
 

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Discussion Starter #5
Got a decent amount of crud out during the heater core flush. I canceled my trip to MT due to big storm (and no heat). Hoping this solves the issue -- but I would like to chase any other viabilities while I have the car in my garage and have the time today to further throubleshoot the issue. I do not have VAGCOM so I cannot check the flaps and actuators. Any other ideas? Just to confirm, this is the version that does not have climate control; I have regular manual controls. So as I understand it, there is not temperature sensor in the cabin then like a CC controlled version... ruling this component out as a contributing player. What else is there? It is blowing cold on both sides (driver/passenger) with the heat turned on full blast (and I have the same temp almost; withing 10 degrees, inlet vs. outlet at the heater core hoses.). Any takers???
 

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If it's the blend door it's the main one at the heater core, in the center of the dash. In a 2008 with manual HVAC ("Climatic") I believe it's still cable-actuated (later Climatic systems have electronic actuators, basically the same as Climatronic/automatic control but without the automatic part). Take a look at parts diagrams from vw-parts.com or similar to get an idea of where everything is.
 

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Discussion Starter #7 (Edited)
Thanks for chiming in -- I realize these HVAC threads are not very popular or "exciting"... and so many do not respond or contribute. But in the dead of Winter... this "little problem" of no heat in the cabin is all of a sudden not so little. It's a big deal to get my heater working again and so I appreciate all the help and insight people are willing to give. Your conclusion of the blend door being central and just off of the heater core itself I would say is correct and partly verified by my own ears. As I turned the dial (and my dial is drive-by-wire, not cable driven), I could hear the actuator (mostly from the passenger footwell side, toward the center column) trying to carry out the commands but then stuttering and finally binding and getting stuck (whenever I set it to any position above the coldest). So it is the main temperature flap actuator that is at fault -- it is causing a no-heat condition on both the passenger and driver side and under all conditions. I am now searching for a reliable schematic for my climatic (not climatronic) system so I can locate the part and the procedure for replacement. Any help toward this end is greatly appreciated. So far, I have located the following part number: 3C1907511F
 

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I think this might help--replacing the "temperature regulator door motor". It's for a 2010 but the system seems to be the same as yours:
 

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Discussion Starter #9
I think this might help--replacing the "temperature regulator door motor". It's for a 2010 but the system seems to be the same as yours:
Thanks for the help. 2010 is compatible, although this is for the CC (climate control) version.. but it will help as a template for removing dash panels and perhaps beyond that a bit (the guts of the CC version are different in some key areas). Just need to know if the main temp flap is accessible from driver or passenger side (I can hear it most from pass side but don't want to assume). Sadly, all the information on this issue is only for the climate control versions.
 

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This might help. It's originally in Russian and is for Climatronic, but the V158 actuator in the Climatronic system looks to be in the same location as the one you need to replace:
 
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