Heat Box Replacement - Low Heat Output

I have been trying to determine the source of low heat output on my '96 Passat TDI. Last weekend I replaced the thermostat with a 195F unit and continue to have low output (65F) out the vents even with the temperature guage at 195F.

I was chatting with another TDI'er the other day and the issue of black foam in my vents led him to believe that the linner in my heat box is compromised after 10 years and the air mix is letting too much cold air past the heater core. It makes sense but I would like to see if anyone else has experienced this problem and if there is an alternative to disassembling the entire dash to get to the heat box.
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Tom Phillip
Waldo, WI

If the control cables from the control head to the box weren't installed correctly ( the clips like to cause slippage and the plastic can break on the control head upon reassembly ), then the cable sheath slides and you can lose 1/2" of throw or more which can amount to the inability to fully move the flap. The Bentley manual has a section devoted to adjusting the cables upon installation as well. I've done many heater core replacements and have run into a couple cable/clip issues.

Looks like a Bently manual will be the next thing on my list.

How extensive of a disassembly of the dashboard is necessary to get to the heater core and heat exchange box?

It's all gotta come out. It's not too bad though really...

As I stated above though, the problem is most likely at the control head where the dials transfer the rotary motion into the cables. The clips that hold down the cables are the most common culprit after a heater core R&R.

WOW! If a picture says a thousand words you pretty near sent a book. Thanks for the response.

I will certainly look at the cable first.

Can you estimate the number of hours for a first-time job - I am guessing I would take this on over a weekend - and whether special tools are needed?

No special tools are needed beyond the typical stuff ( allen sockets, phillips, 6mm, 10mm, pliers, I think the steering wheel needs a 24MM or something close to it... ). The only thing that's needed it to recover the AC refrigerant and then draw a vacuum and of course recharge when complete. Some like to break the HVAC unit and only take the heat portion out leaving the AC but I strongly caution against that as the rear clips will not be reinstalled and the case can break during this process.

know what jgg--ive replaced many a heater core--in fords and chevys--trucks and cars--and a few wonderful chryslers---but the passat doesnt even look like a piece of cake--dang----

JOB COMPLETE ... PIECE OF CAKE ... I HAVE HEAT!!!

The job wasn't as complicated as I had anticipated. I got the dash off without taking off the steering wheel (off ot the right side with the Steering wheel down as low as it went). Once I got the front of the air diversion cover (front & center) off by removing the bottom screw and taking off the two side clips (it looked imposible to get to the screws on the side until I realized it was sliding clips that held into the two screw studs) I had easy access to the metal diversion baffles. That cover actually came off before taking out the dashboard.

The two baffles inside the diversion cover were exposed once the cover and dash were off. The first baffle redirects the air between the defroster, vents, and floor ducts. The second baffle directs the air flow into or bypassing the heater core. Both had manufactured holes in the metal and the foam rubber had completely deteriorated ... thus black foam coming out of the air vents. I used a high quality aluminun HVAC tape (good duct tape could also have been used) and then put HVAC foam rubber with adhesive backing on the baffles as well.

Presto ... no more rattling baffles; heat galore! In fact, I have heat within a minute of starting. This will also make the air conditioning more effective because the cool air won't go passively through the heater core because of the holes.

Let me know if you have any questions ... I was happy I didnt have to take out the air chamber - disconnect the heater core or discharge the air.
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tom - from Waldo

I think I remember someone saying they used duct tape in the heat side of the exchanger and the glue melted eventually. He had to do it all over again not to mention the mess it left. I used a simple felt product from Wal-Mart with an adhesive backing to it but never considered going to an HVAC place to see what they have.