mby

I've got some trouble with my 964's HVAC: while the CCU and all servo motors work flawlessly, I've got some trouble with the footwells: firstly, the amount of airflow on the passenger's side (my 964 MJ90 is an LHD) can't be change, no matter how much I move the slider on the CCU, secondly, the one on the driver's side does react but opposite to the movement of the slider (i.e., slider to the left (closed): high flow; slider to the right (open): nearly no flow).

There are no errors visible in diagnostics, so it might be an error with the lever, but how to check and adjust the lever without having to take tank, firewall, fuse box etc. out in order to have access the HVAC unit? – Any workaround to more easily access the footwell flaps and the connecting lever to see if the right-side flab might have become unhinged?

Thanks and best regards
Michael

mby

Still struggling here; anybody any idea, especially regarding how to get access to the footwell flaps without deconstructing the 964? – Thank you!

heliolps2

Hey there, there's the paper hose that goes to a plastic tube that goes to suit case on each side of the footwell. I would remove the Paper hose and pull down the plastic elbow it just snaps in place be careful not to tear the foam gasket, once you do that, you then can peek in there with a flashlight and see if your flap is opening and closing correctly. Try Switching the heat ON, if the flap opens that's good if the flap remains closed try pushing on it, If it moves freely, that means it has become dislodged from the rod or the motor. the flaps should be closed when the AC is ON or with everything is turned OFF, I hope this helps.

Helio

ToreB

There is only one servo motor controlling the air flow to the foot well.
Your message suggests that you may think that the two mixer servos are controlling the air flow, or two flaps. The foot well servo shall open for max air flow when set to the rightmost position of the lower slider ****. There is only one flap for the footwell air flow.
See this page for identification of the servo motors: https://www.bergvillfx.com/categorie...test-procedure
I see you write you have no OBD fault codes, are you sure, which OBD tool are you using? Only a handful of OBD tools can access the CCU. (Scantool with home made serial adapter or T-OBD, Bosch KTS 301 "Hammer", KTS500/PST-2, PIWIS v1/2, Durametric and Jennisken PDT/UDT-999)
If you experience difference in air flow, I guess you have a problem with a mixer servo instead of the foot well servo. If one of the mixer flaps is stuck in the closed position, the air flow will be very weak on that side of the dashboard when the temp **** is set to anything above minimum. (depending on ambient and cabin temp) If so, set to minimum temp and see if the air flow is better. A faulty/stuck servo is very commonly seen, and will produce a CCU fault code.

Cheers,
Tore

0luke1

Move to Honolulu. It’s the same temperature every day.

mby

Thank you all!

@ToreB , yes, that servo motor for the foot wells is moving; I'm using the UDT-999, and it confirms that all temperature sensors are fine. It can't check on the servo motors, as my 964 is model year 1990, but it's easy to feel if they are moving, so at least some feedback. From what I understand the servo motor for the foot well flaps has a rod to one of the flaps and both flaps are connected (and synchronized) via a separate rod. – As it looks now, the flaps do not close properly, so my primary problem is how to check on those without having to extract the entire HVAC unit in the frunk.

@heliolps2 , I've tried to peek in but somehow I couldn't see anything.

@0luke1 , moving to Honululu is not an option as it is worse in warm climate with AC on.

heliolps2

Did you remove the plastic elbow the paper hose connects to in the footwell? the flap is right there and you should be able to touch it with your fingertips and see it. another way is to remove the clips form the covers that house the fans on the left and right sides of the suitcase from the trunk. Once you remove the covers you will be able to see the rod and flaps clearly. It's PIA, The 993's is far easier because it's meant to be serviced and houses the cabin filter in that area. The 964's not so much. Don't drop the clips.

Metal Guru

San Diego too
It's easy to see if all the servos are working as they are all mounted to the top of the suitcase. You should verify this is the case before going any further.

mby

Thanks all and will try as suggested, @heliolps2 !