constant heat from interior climate control system

Having an issue with the AC/ventilation system in a 2004 Jetta TDI.

For most of the winter, the system constantly spewed hot air only, and did not respond to adjustments of the temp control on the dash.

Regardless of the control position, it was always HOT air.

Suddenly, a couple of weeks ago, the controls started to behave normally again.... which made me cautiously optimistic that through some divine intervention the problem had resolved itself.

Today the magic spell expired, and the system has resumed pumping hot air into the passenger cabin.

Can anyone with knowledge of how this heating system works offer some suggestions of how to approach this?

Is there a valve to control coolant flow through the heater core that may be stuck? Is it manually controlled by cables/levers..... or perhaps vacuum operated?

If not a valve, could this just be an issue controlling the direction of air flow thorough the ventilation system?

Can this be realistically diagnosed or serviced without dismantling the entire dash in the process?

Some hints as to where to start investigating or troubleshooting would be very much appreciated.


Thanks

It's a flap that directs the flow of air through or passed the heater matrix, cable operated.

Maybe whatever holds the cable sheath is loose or damaged.

Where it is on your car I'm not sure, on mine it's up under the left side of the dash but I'm in the UK. There's the blower motor etc all up in there

Search blend door pin. It's a plastic piece that attaches the lever end of the cable to the blend door. When they get brittle, they pop down and the heat stays wherever it was last set. Typically they don't start working again on their own though.

On US cars, it's on the right side of the car, under the dash behind the center. There are you-tube videos of them being replaced. FYI - I can replace them without much removal or cutting of trim pieces (recommended in some videos). The video will at least show you where it's located.

Last I heard, VW had discontinued this part. I got lucky and bought 2 when I needed one 2 years ago.

Coolairvw has a friend 3D printing them, and he started a thread to let folks know.

Tdijarhead said:

Coolairvw has a friend 3D printing them, and he started a thread to let folks know.

Click to expand...

I saw some mention a while ago and even saw images posted. That's definitely something we need to happen! I should bring the one I have into work and see if they can do it here...

Thanks for all the tips, guys! I guess I will be spening some quality time under the dash this weekend!