97 855 Fan noise coming from dashboard, NOT the blower motor

[Py]

Hello,

I'm the very happy owner of a 97 855 which is going strong at 294k km. I'm in the beginning of the process of fixing the whole climate control stuff - I've an ECC (basically, evaporator is leaking, and some DTC are showing up).

For the last years, I sometimes had a high pitched "squealing" coming out of the dashboard. It didn't change when I changed the blower speed manually, but I still was under the impression that is was caused by a fan or at least something rotating, with tired bearings.

Well, for a few days, the complete blower assembly has been out of the car as I'm waiting for the replacement motor, and the noise came back anyway. So definitily it is not the blower motor.

Is there any other fan or rotating device inside the dashboard? I only know of 3 fans (one in each temperature sensor, above driver and passenger heads, third being the blower motor). Temp sensors are definitely not making any noise, blower is out of the carn, so what could cause this noise? Like all intermittent noises, it obviously never does any noise when I'm trying to locate it, making it more difficult to locate. I feel like it's coming out of the dashboard vents...

As I'm going to take the whole dashboard apart in the next few days, now is the time to figure out and to fix it, IMHO...

Thanks in advance guys!
Py

[abscate]

It could be one of the damper motors from the ECC whining perhaps? If you toggle controls on the ECC can you get the noise to change ??

[Py]

Hum, didn't think of this possibility... For an unknow reason I'm now realizing that I always assumed that damper motors were basically silent units, or at least that they can not make this kind of high pitched, rapidly oscillating noise. Which is probably just plain wrong.

What makes troubleshooting this noise extremely frustrating is that it only starts randomly, and stops a while after. It can stay silent for weeks, or get noisy several times the same day. I have the feeling that it is more often noisy in cold weather (so much for me trying to fix it in the summer...). Once blower is reinstalled (hopefully tomorrow), I'll fiddle with the settings on the ECC as soon as the noise comes back.

I also happen to have ECC DTC code 222 set, which is "Passenger’s side damper motor position sensor shorted to earth". I have yet to perform more tests to figure out what's going on there (Volvo's documentation is very detailled about the troubleshooting steps for such a problem), but at least I've a suspect damper motor...

[Py]

Quick update: system is completely reassembled including blower, however the noise did not come back yet, so no chance to fiddle with it. I played with the air outlet setting button quite a lot, at various airspeeds, but couldn't trigger it.

On a side note, after all other fixes, and despite airspeed control working just fine, I still have a code 419 left, and coming back again right after having been cleared (DTC 4-1-9 ECC POWER STAGE EMITTING FAULTY DIAGNOSTIC SIGNAL).

Any idea on what could cause this on a seemingly perfectly working system? Should I get another power stage and test with this other one?