[79Mercy]

We just had a cold front come to us and the other day I was trying to get the heat on and it would not come out of the drivers side vent only cool air would come out. On the pass. side vent heat would come out and nothing out of the center vents(nothing has ever come out of the center vents for years). Why doesn't it come out of the drivers side vent? Thanks

 

[Chaw]

Could it be the ACC Servo gremlins?

 

[79Mercy]

I did replace my servo about a year ago. Why would that make heat only blow out of the pass. vent?

 

[DOUGLAS MARTIN]

Odds are you have a vacuum module leaking. Maybe more than one. AC only comes out of center vents, heat only comes out of side, floor, and defrost vents when system is working properly. The vacuum modules, pink lozenge shaped plastic actuators tucked away behind and under the dashboard, open and close flaps directing interior airflow and can be repaired at minimal cost with elements from George Murphy. If you don't have a miti-vac already, now is the time to get one.

 

[79Mercy]

I didn't know that the side vent had a vacuum module. The floor vent vacuum hose has been plugged to make the air cond work and not go on and off going up hill. Is there any way to open the side vent and let it stay open and never close like removeing the mod.

 

[DOUGLAS MARTIN]

Try restoring all systems to as designed for proper airflow management.

 

[79Mercy]

If I do that I can't get heat at all. and the air will go off under acceleration. I have a big vacuum leak under the dash somewhere and I ican't pull the dash rright now to find it.

 

[MBeige]

I've always thought that the side vents were always open, that the vacuum modules only controlled the center vents. When they go, the center vents don't puff out any air and are stuck closed.

Make sure the corrugated tube inside is still attached too. If it doesn't have heat but has cold air on the driverside vent, then it's probably something related to controls. Which climate control do you have again?

 

[DOUGLAS MARTIN]

The vacuum actuators open flaps that allow air to flow from plenum to vents - if not air would flow all the time - at temperature selected via dash control unit and dreaded servo, in conjunction with vacuum switches behind and under radio / ashtray. The center vents are only for AC. Nearby the driver's right foot are two vacuum actuators - a single and a double diaphragm - that the dash need not be removed to access. You will have to remove under dash plastic panels for access. Check them out. Removing glovebox will allow access to other actuators while dash is in place. The system is dependant on being leak free for proper operation. When you discover the leak - it may just be a connector - the system will work.

 

[79Mercy]

I get air out of both vents but no air has ever come out of the center vents. A week ago I had heat out of both vents it was just all of the sudden only air cond would come out of the drivers side vent. The blower is moving heat so why is it not coming out of the right vent.What i'm trying to say is where is the air cond coming from if the air cond is not even on?

 

[79Mercy]

I've always thought that the side vents were always open, that the vacuum modules only controlled the center vents. When they go, the center vents don't puff out any air and are stuck closed.

Make sure the corrugated tube inside is still attached too. If it doesn't have heat but has cold air on the driverside vent, then it's probably something related to controls. Which climate control do you have again?

I have the early controls. The other day t was very cold inside the car so moved the wheel to in between 70 and 75 and cold air still came out of the drivers vent while the warmer air came out of the pass. vent. What does this mean? Thanks

 

[MBeige]

Is it as cold as when you have your AC on? If it is that may sound like an electrical issue, if not (just plain outside air) then I would suggest following Douglas' advice on the vacuum actuators and see if you have leaks.

If yours was similar to mine I would say the lateral vents are always open, I've never had them shut off as in controlled via a flap. The center vents like I mentioned are flap controlled and this is usually because of the center vacuum actuator in front of the dash, right below its surface. It may have been exposed to the sun and has had its diaphragm ripped, so it's not working as it should be. Hence, no air in the center vents.

 

[79Mercy]

Is it as cold as when you have your AC on? If it is that may sound like an electrical issue, if not (just plain outside air) then I would suggest following Douglas' advice on the vacuum actuators and see if you have leak

It is not as cold as the a/c would be.

 

[boneheaddoctor]

You only get air out of the center vents running A/C or when the vent function is working which is basically when the temp dial is set at ambient temps in a certain range. Yeah I wish it blew heat as well, but the engineers at Mercedes felt differently.