Hi there,

I've been living with this issue for 15 years and now I am determined to resolve it, if possible with your help :roll:

Essentially, when the heat control knob is turned to the min. it makes a tic tic noise, in order to get rid of it, I have to slightly increase it.

I remember at the beginning of 2000 a Volvo dealer told me that is was better to leave it as it is as it was not easy to resolve, but I do not remember the explanation they provided to me or perhaps they did not... honestly I do not know.

Anyhow, I just recorder this short video in order to let you hear what I mean (I do apologize for the video sponsor at beginning/end of the video, I used a freeware software).

The video is with engine off, key turned to II, if I leave it in that position (coldest) it stops the noise after approx. 15 secs.
The noise seems to come from the back of the central unit.

http://www.mediafire.com/file/64en9bxh74nd4dn/Heat+Control.mp4

I really hope some of you can help me to figure this out.

Thank you!
Alex

Hi Metallo,

I haven't had this thing happened to me but knowing how the manual 940 HVAC system components work I would venture a guess. Thats your blend door MOTOR's noise (Item no. 32 in the diagram below).

The heat control knob controls the MOTOR that moves an air blend door within the HVAC enclosure. The air from blower --> AC evaporator --> heater core (this is where the blend door is). In other words the blend door lets air BYPASS or GO THRU the heater core thus giving you temp control. There's NO motor inside the HVAC control unit (I've opened the control unit to re-solder the troublesome AC relay sometime ago so I know).

You'd need to dismantle out the knee cover panel beneath your steering in order to see how the blend door MOTOR works. Shine a torch to the area behind the HVAC control unit. Engine OFF and ignition to KPII, move the heat control knob and you'll see some HVAC parts (Items no. 33 to 36 in diagram below) moving at same time. When the noise happens inspect further at the noisy area.

Possible causes of noise:
1. Worn blend door link rod - undue looseness there
2. Worn blend door MOTOR - dismantle this MOTOR out then test its movement with the heat knob again
3. Stuck blend door at extreme ends of movements (could be foreign body in HVAC enclosure causing this)
4. Faulty HVAC control unit - this rarely happens



Items no. 33 to 36 - blend door links - inspect these
Item no. 32 - blend door MOTOR - could be dismantled out to see if noise comes from motor itself


Good luck,
Amarin.

Hi Amarin, Spook,

Thank you very much for your insights.

As soon as I have the time I will look into this, I never had to work in the HVAC system before, therefore I will need some instructions on how to get to the servomotor (I believe this is the way they call it in VIDA).

Thank you for now,

Alex

Dear Amarin,

Hope you're well. Great analysis!! I suspect the blend door motor is a sealed unit. This part (#3522797), happily, is still available from Volvo (about US$240 at a North America dealer).

Hope this helps.

Yours faithfully,

Spook

Dear Metallo,

Hope you're well. As no one has reported a similar problem and a solution to it, I offer some suggestions.

Is the radio "on", while this noise occurs? If so, turn-off the radio and see if the noise is still present when the "heat control" knob is at the
"minimum" setting. If the noise "goes away" - when the radio is "off" - there may be a problem internal to the climate control unit. It may generate a "signal" that the radio "broadcasts".

If you have a spare climate control unit, install it and see if the noise "goes away". If the noise ceases, then the problem has been found: there's some problem with the climate control unit.

The noise plainly does not emanate from the climate control system fan (not running), the air-handlers (not moving), etc.

Hope this helps.

Yours faithfully,

Spook