No heat from two center vents

[uneasysunday]

Hello Benz gurus... I have a 1979 240D with manual climate control. I have heat coming out the defrost vents and two side vents near the windows but only cold air blowing out the two center vents. Is this a tube in the dash disconnected or a flapper malfunctioning? Was hoping someone here has had the same problem and could lead me in the right direction for a fix. I probably should have taken a flashlight and looked under the dash before posting this but any responses would be greatly appreciated...

Thanks in advance.

[Biodiesel300TD]

The system in the 123's isn't design to send heat through the two center vents. They are ment for the fresh air flap in the non-AC models and AC in the models with AC. So your system is working as it should.

[charmalu]

X2, just fresh air in the center vents.

I was surprised on day when I discovered you can really get a blast of hot air if you turn the AC Knob a little to the right. My AC is disconnected, but the knob opens up a vac pod and then really sends a rush of air. nice on a cold morning/night.

This is on my 80 240D.

Would be nice to get hot air from the center vents. but still much better than our 85 300D.

Charlie

[Jeremy5848]

In a 123, it's possible to disconnect the center flap from the controlling vacuum pod and then get center heat. You can still control the output of the center outlets manually with the knobs.

The procedure involves removing the glove box liner and pushing aside the rubber piece that connects the two center outlets with the CCU. You can then snake an arm in through the glove box opening and touch the flap and the flat metal piece that connects it to the vacuum pod. The metal piece is connected to the flap by a plastic pin. You'll have to use a long, slim screwdriver to pry the plastic pin out while holding it with your hand so it doesn't fall into the innards of the CCU. Insert the screwdriver through one of the center pods and use a 3rd hand to hold a flashlight so you can see what you're doing.

With the pin out, you can open the flap and jam the flat metal control arm across its top. That keeps the flap open at all times. Then find, disconnect, and plug the vacuum outlets that go to that pod. If you don't disconnect the pod, it'll keep trying to work and will eventually pull the arm free, allowing the flap to fall closed. If you don't plug the vacuum outlet you'll cause a leak in your vacuum system any time the climate control is on in "cooling" mode. My pod didn't work anyway–it's diaphragm was shot–but I disconnected it anyway to stop the vacuum leak.

The picture shows the metal control rod jammed across the top of the flap, keeping it permanently open. Now put the rubber piece and the glove box liner back and you're done. Don't forget to put the plastic pin away so you can reverse the mod if you ever want to. You will now have air from the center vents in all ACC operating modes. To get more air to the defrost, side, or bottom outlets you'll have to close the center vents manually.

Jeremy

[andrewjtx]

But modding the center vents to get heat out of them would rob the footwell vents of airflow. I'd rather have warm feet first. The rest of the car will warm up pretty damn fast once the engine is up to temp.

[wilburtual]

so if no heat is supposed to go thru the center vents, the sliding knob control under them is just to turn the fresh air on/off? as in, when the heat is on, they should just be turned off?

[Jeremy5848]

Originally Posted by andrewjtx

But modding the center vents to get heat out of them would rob the footwell vents of airflow. I'd rather have warm feet first. The rest of the car will warm up pretty damn fast once the engine is up to temp.

Not in my experience ('85 300D-T). If so, you can always partially close the center vents.

[Jeremy5848]

Originally Posted by wilburtual

so if no heat is supposed to go thru the center vents, the sliding knob control under them is just to turn the fresh air on/off? as in, when the heat is on, they should just be turned off?

Ah, you have a different system, possibly ACC-I or -II. My '85 300D-T had an ACC-III system so there is no sliding control like yours. I am not informed of how that system works so I can't advise you.

Jeremy

[wilburtual]

Originally Posted by Jeremy5848

Ah, you have a different system, possibly ACC-I or -II. My '85 300D-T had an ACC-III system so there is no sliding control like yours. I am not informed of how that system works so I can't advise you.

Jeremy

on both my 77 240D and 81 240D there is a horizontal sliding knob under the vents with an arrow on it,it seems to turn them on and off, but im not really sure, since i dont know if my system is working how its supposed to i would assume the OP's 79 240D would be similar to mine

[Biodiesel300TD]

The sliding knob just opens and closes the fresh air flap. You'll only get ambient air out of the two center vents. And the eye-ball sockets on the dash will not have an open and close feature like the two outer ones do. Atleast thats out my 78 240 is. But I also don't have AC. So the only thing that comes through the center vents for me is freshair.

[charmalu]

Originally Posted by NakedApe

That disables defrost and floor heat to get the extra flow.

This is true, the full flow will come out the 2 side vents, and not any to
the floor or Defroster. turning the AC knob to the left will activate the Vac Pod and close the door to resume air flow to the floor and defrost.

But when Iam cold it sure feels good, and warms my cold hands.

Charlie

[uneasysunday]

thanks for all the expert info guys, this is why I love this forum and will never let my 240D go...