Diagnosing blend door/heater core

Gingy22

Member
Joined
Nov 12, 2017
Location
Currituck, NC
TDI
2012 Passat SE
I'm having an issue with the pass side blowing cool. everyone seems to say HEATER CORE. However my '12 SE Passat is not covered under the extended warranty (however VWoA is willing to cover it IF that is my issue). I need to be certain my heater core is the culprit before i drop it by the dealer for official diagnosis. What are the tell tale signs for diagnosing this? How can i actuate the blend door so i can verify it's working properly? Ive searched the youtubes and on here and can't seem to find a good thread with pics. If you know of one please shoot me the link. thanks.
 

VeeDubTDI

Wanderluster, Traveler, TDIClub Enthusiast
Joined
Jul 2, 2000
Location
Springfield, VA
TDI
‘18 Tesla Model 3D+, ‘14 Cadillac ELR, ‘13 Fiat 500e
With the car fully warmed up (this requires a >10 minute highway drive), turn the heat on full hot on both sides with the airflow direction set to face. Measure the vent temperatures with a thermometer and compare the left side to the right side.

If you have VCDS, you can scan the climate control module to see if it has a stuck blend door. It will set a trouble code if it gets stuck. I think this is unlikely, but not impossible. Your dealership should be able to do further diagnostics if you go to them and say the driver's side is 140F and the passenger's side is only 90F (for example).
 

Gingy22

Member
Joined
Nov 12, 2017
Location
Currituck, NC
TDI
2012 Passat SE
Thanks. I'll do that today. I do not have vcds so is there a visual cue that could tell me if the blend door is not functioning?
 

VernK

Veteran Member
Joined
Jul 31, 2012
Location
Kelowna
TDI
2012 Passat 2.5L Gas
I had a blend door motor fail (at least that was the symptom, though I got the bad part back and it runs on the bench) but it failed with the door in the hot position. I don't know if that's random or telling.

Yours
Vern
 

Gingy22

Member
Joined
Nov 12, 2017
Location
Currituck, NC
TDI
2012 Passat SE
I can see what I'm sure is the actuator sweep when moved from full hot to full cold. And it moves fractionally when adjusted to a temp in between. I'm pretty confident now that the blend door is working.
 
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