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A3 Poor heater output

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QuickTD:
The current cold snap has me wishing my heater worked better. At present it only blows lukewarm to cold. The heat is not sufficient to defrost the windows, even after an hour of driving. I have to keep a credit card handy to scrape the glass as I drive. This has been an ongoing problem with my car (97 jetta 1.9TD). Needless to say its getting a bit tiresome. The coolant temp reads normal (90ºC) and I have stuck a thermometer in the reserve bottle to confirm the temp as well. Both heater hoses are hot as well. I have monkeyed with the blend door adjustment to ensure that it is in fact going all the way to "heat", so far no joy.

 I'm thinking its a problem with airflow through the heater core. The hot heater hoses would seem to indicate that hot coolant is reaching the core but the air must be bypassing it somehow. Has anyone had an A3 heater heater box apart? I'm wondering if the blend door is covered with foam like the A2's and its disintegrating. I haven't noticed any foam coming from the vents, but you never know...

Patrick:
It's a lousy time of year to do it, but the first thing I'd do is pull the lines off the core and hook a garden hose up to it, and run water through it , both directions three or four times. If anyone ever put any kind of leakstop in it, it could be partly plugged. Ran across this a few times, and it's an easy fix if that's what the problem is. Go for the air doors and the vacuum controls after that.

fspGTD:
QuickTD - does your '97 have one of those cabin air filters?  When those get clogged, the defroster stops working effectively.  I've got a B4 (1995) Passat VR6 wagon that is about 2000 miles short of having the cabin filter service interval trigger a replacement, but it's not defogging effectively and the airflow out of the defrost system seems inadequate.  I think it's a clogged cabin filter, so I'm going to go ahead and replace the cabin filter even though it's before the interval.  The car just can't get defrosted with this clogged cabin filter...  I can't remember if an A3 model like yours has the cabin filter or not, but it's definitely something to check out...  good luck.

QuickTD:
No cabin filter (GL model, not GLS) and the airflow is fine, just cold. The heater core has been flushed with both compressed air and running water. The cooling system has never seen any "stop leak" treatments, it has never had a leak. I can assure you the heater core is clear. Both heater hoses are very hot while the heater continues to deliver poor heat. The coolant has been changed a few times and is clear, never had any rust or sediment. It has to be the blend door, its the only thing I haven't touched... I'd like to hear from someone who has been into an A3 heater box. I want to confirm my diagnosis of failed foam covering on the blend door. Has anyone seen this? Same as an A2?

Patrick:
Haven't been into that car specifically, but it sounds to me like you've covered all the bases. Looks like you've got to get into the box, something's got to be letting the air flow past the core instead of through it! Is there vacuum controls on the door? something plugging the outside of the core? Just guessing...................

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