There is no floorwell heat coming from the heater of my 300D, even though eveything else, switch, panel lights, etc., seem to work fine. I get plenty of warm air volumn out of the panel vents, and plenty when selected to "Defrost" but there seems to be no air at all emenating into the floor areas.
Suggestions?
In any position except defrost, does the heat blow out the defrost and up to the windshield?
If yes, you have a vacuum leak somewhere in the dash.
By law, all automatic climate control systems must default to defrost if a vacuum part fails.
Do you 5 buttons horizontal or 5 buttons vertical?
Thank you very much.
First of all, five buttons vertical.
And yes, I do get warm air out the windshield defrost vents when the heater control is selected to "Bi-Level". And for what it's worth, there are other vacuum problems, because prior to my acquiring the car, someone altered the vacuum hose arrangement where a number of hoses join at a place under the hood just forward of the driver. One vac hose has been plugged off. As a consequence, the cruise control doesn't work, and only the rear vaccum door locks work. I believe this was done due to a vac problem that probably caused the engine not to shut down with the ignition switch.
I do not as yet have the MB shop manuals for the W123 300D, and so I cannot diagram what should be in place with respect to the vacuum hoses, so in order to completely restore the system back to its proper configuration, probably requiring a shop procedure.
In any event, is it your belief that the vacuum is not opening the lower heat vents?
It definitely could be a vacuum problem, as that is what is used to move the actuators that put the flaps in the proper position to control where the air goes. That is where I would start, especially given that the vac system has other serious problems as well.
I take it this car has automatic climate control? If so, then the next candidate unfortunately is the servo and servo amplifier. The servo is the plastic widget about the size of two fists, located under the hood, near the passenger side firewall. It has 2 electric harnesses, 4 coolant hoses, and a bunch of vacuum lines connected to it. (Begin to see why it's failure prone? :) Take a look at it, and if you see any coolant leaking from the lower portion of the servo, it's either shot or on it's way out.
Google here for AC servo if necessary and you'll find plenty discussion about it.
One tip to prolong the life of the servo. About once a month, put the temp all the way to max for a few mins and let the car get fairly warm inside. Then move it to max cooling, and leave it there for a couple mins. That moves the servo from full cool to full heat and cycles it through it's full movement. It helps keep the rheostat inside from developing dead spots, keeps the gear lubricated, etc.
When you do that, if the system is working correctly, you will hear the blower slowly drop down through it's various speeds from max heat speed to lowest, then cycle back up to max cooling speed. The highest cooling speed is one speed higher than max heat speed. At the same time, the air should switch from coming out the footwells in heat mofe, with some bleed air to the side dash vents to all coming out from all the dash vents in cooling mode.
Very helpful information. Thank you very much!
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