Ron_H

I used the Audi valve. It is all metal and seems more robust. I don't have a part number, unfortunately.

kraft

on 944, when this occurs, it's often due to a few cents plastic part which keeps a little pin on one endless rail that a litlle motor makes turning on itself, opening and closing a flap. The principle of this thing is the same as on some floppy head rail coupled with a little motor.
I know 944 is not equal to 928 but this is very similar to a trouble i used to have in the past with my hvac.


Oh yes the part is located under the wheel, near the console...

Tim Emsky

Brian, The mixer valve makes sense, but I haven't been able to locate it in the service manual. Can you guide me to some info on this valve?

bd0nalds0n

Check out page 87 - 43, there's a picture of it there. They call it the "control unit." Unfortunately, there's not a lot of other information, but this may help you identify it under the pod.

The control arm hooks up to a lever that traverses behind the center console to operate the heater flap on the other side. If the AC gets too cold for the temperature set, the mixing motor control unit opens the heater valve and modulates the flap to the heater core to warm the AC air.

Found more info--called the "setting motor" on page 87 - 113 thru 115.

Tim Emsky

Brian, Thank You. I will order one today from 928 Specialists. This is crazy; I have the heater valve wired SHUT, and it is still blowing hot air. I'm assuming it is air from the engine compartment coming through.

bd0nalds0n

Well that could be something completely different--heater valves have been known to fail INSIDE so that even though the arm closes, hot water still circulates because the valve doesn't close. [Edit: I see you have a new one...]

Did you check the solenoids at the vacuum manifold to make sure they're each receiving power, and losing power (e.g., activating the various vacuum-actuated pods) when they're supposed to? With my faulty mixing motor, the solenoid that allows the heater valve to receive vacuum was never electrified...

Tim Emsky

Brian, I will try the solenoids next. The control unit (mixer) seems to be operating correctly; in the down position for cool temp, and the rod raises when temp control is set higher.

bd0nalds0n

Yes, if the hc valve solenoid does not get energized when the control unit is in the cold pos, my bet is still the control unit, as the power comes from it.

the flyin' scotsman

Tim.......remove the hot water valve and check that its sealing closed.........if not glue it. Next make sure the recirc flap is open so your bringing in fresh cool outside air...........its open when down toward the fuse panel. All that done you've bypassed the auto system but for a pure manual system check our Tony Harkin's site for bypassing most of the system.

Also, check out john Pirtles site for a real good write up on the HVAC system.

Tim Emsky

Brian, the hc valve will close when the temp control is turned off, or when the AC switch is depressed. Would this indicate that the control unit is energizing the hc valve solenoid? i will also verify voltage at the solenoid later just to be sure.

Malcolm, I replaced the hc valve even though the original seemed okay. It absolutely closes, as I tested it before installing the new one. Can you point me in the direction of Tony Harkin's site? Moving to a manual system is looking pretty good at this point.
I've also gone through all of John Pirtle's info which is excellent material.

AO

Tony's site.

http://members.rennlist.com/v1uhoh/

bd0nalds0n

Well if the heater valve closes when the AC switch is turned on, then why are you still getting hot air? Doesn't make sense.

bd0nalds0n

You might want to make sure the heater valve has been installed correctly; I think I read in another post somwhere that if it's installed backwards it will flow even when closed.

the flyin' scotsman

Tim............as Brian suggests the hot water valve is the only way for hot engine coolant to flow into the interior. If the valve is closed should be getting no hot air except for the outside ambient. As per Tony's site having the recirc, center comb and floor actuators connected to the direct vaccum source and the hot water valve colsed you then have max cooling from the A/C; if working?

AO

FYI... I've had heater valves that looked like they are closing, but still allow quote a bit of water to pass through. The only way I know to test is to pull it, and then blow on one end while holding it closed. (rinse it off first... antifreeze doesn't tast good.)