Climatronic Error: Troubleshooting & Repair

Hello,

I'm tracking down an issue with my Climatronic system (Passat Variant 01 AWX) and could use some help because I'm stuck.
I was wondering why it always takes about 20-30 seconds after starting the engine for the fan to start and for the level indicator to appear on the control panel. When only turning on the ignition without starting the engine, the fan only runs when the buttons for the fan speed levels are pressed.

Once, there was a bug.
Control unit part number: 3B1 907 044 J.
Component or version: CLIMATRONIC B5GP 0004
Software Coding: 17000
Workshop Code: WSC 44938
Sure, here is the translation of the text from German to English:

"1 error found:"
01341 - Control unit in the instrument panel carrier, Comfort CAN (J285).
27-10 - implausible signal - interrupted.

I deleted it. After that, no further errors occurred. The diagnosis is running perfectly.
The workshop says it's working perfectly. However, something must be wrong because the fan used to turn on after about 2-3 seconds after the ignition was switched on, regardless of whether the engine was running or not.
Since this morning, it's happening again. The fan starts running briefly after the engine is started, even when only the ignition is on. There was no error message displayed today either.

Can someone please give me a tip?
Thank you.

Let's run a diagnostic test on the actuator; that will give us more information.

If I can do it myself using VAG-COM, what steps should I take?

uk wrote:

If I can do it myself with VAG-COM, how should I proceed?

VAG-COM > Selection > 08 - Heating/Climate Control > Actuator Diagnosis - 03.

Okay, so I've done that now, but it seems everything is fine. He also didn't find any errors. However, the fan still isn't running when only the ignition is on, just like I described before.

Did he run the actuator diagnostic? Does it run when the engine is on, or does it make a difference whether the engine is warm or cold?

"On my A4, it also takes a while for the fan to turn on when the coolant is still cold. However, I can manually turn it on using the control buttons."

Yes, that worked. As I said, it takes 20-30 seconds for the engine to start, and you only need to turn on the ignition. To start it, you have to "nudge" it with the faster or slower buttons. Except this morning, it worked correctly again; it started immediately, even when the engine wasn't running.
The fan is running on all levels, which is why I believe the problem is not related to the fan itself.
If I remember correctly, until recently it didn't make a difference whether it was warm or cold.

It's possible that a temperature sensor is providing incorrect readings. Please check the sensors for plausibility when the car is cold; they should display approximately the same values, within a range of +/- 2°C.

You mean: Press [ECON] + [Cooler] + [Fan Speed Low] simultaneously, then the channels:

01. Temperature setting (on the control panel of the Climatronic system).
04 Average temperature of the bumper.
05 Temperature bumper - current value.
06 Temperature, fresh air intake duct.
07. Outlet temperature of the footwell.
08 Outlet temperature, specify value.
23. Actual value, outlet temperature, middle.
24. Setpoint for outlet temperature.

Did I forget something?

No, not that stuff. Use VAG-COM.

I just tried to read the temperatures, but I probably didn't have the correct label file, so I had to manually press the buttons on the control panel. As far as I can tell, the values seem to be approximately consistent.

The fan was running again, both when just turning the ignition on and immediately after starting the engine.
It had been standing there overnight. Let's see what it's like when it's warm.

uk wrote:

...but probably no suitable label file...

It's strange, VAG-COM has had a label file for this Climatronic control unit since August 2001...

I tested it again, and the file is there. I wonder what was going on.
Even there, the temperatures are almost all the same.
Is there a relay there that might be malfunctioning?