"that small vent" in center of dash

[rememberjeff]

I lifted up that small vent in the middle of my dash (85 380 SL).
I wanted to check the connection. When I lifted it up, it disconnected from
its source. Now I cant seem to fish it out of that hole and reconnect it.
Not theres any easy way to do anything in these cars, how can I
get that wire under the vent hole and reconnect it?
thanks.

[RickM]

Do you mean you disconnected the rubber "hose" from the back of the plastice vent body? If so just remove the glove compartment liner and you'll have decent access.

[airedale]

What is that vent and hose for?

[rememberjeff]

I fixed it, but I believe its a temperature sensor.

[cbdo]

It's the interior temperature sensor duct for the ACC. There's a small blower in there somewhere that draws cabin air in through there to the sensor that tells the ACC what the interior temperature is.

[carcentric]

Mine's been covered with a clock!

[cbdo]

Carcentric, unless I'm mistaken he's asking about the little grille on the top of the dash, not the middle of the three "eyeballs" (which may be a clock, a vent, or an outside temp gauge). Rememberjeff, please correct me if I'm wrong.

[rememberjeff]

Yes, its the very small grill on top in the middle of the dash. The ACC that you guys speak of; is that overridden , or supposed to be overridded when you turn the temp wheel to either extreme, heat or AC? I get intermittent heat or no heat now and ordered a mono valve replacement , which I see recommended on other posts. You guys agree??

[cbdo]

Do a search of the site and you'll come up with hours of uninterrupted reading pleasure. At full hot or full cold, it should automatically go to constant max heat or cold; at anything in between, it will use the sensor as its source for current cabin temperature. The hose that feeds the sensor can degrade and/or get gunked up with dust, etc., and degrade the system's ability to know what the temp is. The monovalve, when open, allows coolant flow into the heater core; since its failure mode is open, a blown monovalve diaphragm results in uncontrollable full heat, though it may go through a stage of intermittent behavior when there's just a small defect. A variety of misbehaviors can come from corroded or dirty contacts in and at the switches and the temp-dial potentiometer on the control panel; it's not hard to get the panel off and tend to these. Finally, the vacuum lines to the actuators that control the various dampers to direct air flow, and the actuators themselves, are occasionally candidates for attention.

[DavidSoine]

I seem to remember no heat as another monovalve failure mode on our car...

Our car lately doesn't seem to be blowing as hot as it should - I wonder if I knocked off that tube during one of my trips into the dash this summer??? It does blow HOT when the wheel is turned all the way.

best,

Dave
87 560sl

[cbdo]

For those who haven't had to dig into it before, the monovalve is essentially a solenoid hooked to a rubber membrane. In rest position, it allows full flow into the heater core. When activated, it closes off flow thus reducing heat to the cabin. If the rubber membrane is torn (which is the most common failure), or if the solenoid doesn't function, you've got heat you can't stop. It would be much less common for the solenoid to seize in the active (no-heat) position, but not uncommon for faults elsewhere in the system (control circuits, airflow dampers and their vacuum actuators) to produce less heat than you want.

[rememberjeff]

Craig,
Thanks for your input. I ordered the part and now I know what it does!
You comments seem contradictory to other comments.
Numerous other posts have said that they have "little or not enough heat" and when they replaced the monovalve it solved the problem.
I havent had the chance to replace it yet, so Im curious what the outcome will be. Thanks again.

Jeff