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1996 Mercedes E320, the HVAC control on the dashboard no longer changes the direction of the airflow. Blower motor works fine. Currently in the airflow mode of defrost and floor. Could be the controller failed, could be a door/flap actuator(s) failure. Need to know how to test both, or is there a high failure rate of any of these components. Have been on a few MB forums but have not found anything specific.
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It seems like the HVAC functions are vacuum operated. It sounds like you’re going to need a vacuum pump and some manual information to try and start tracking the issue down.
Thank you for the direction. Not to be difficult, but I pulled the HVAC control from the dash and there are only two fairly populated electrical connecters that plug into it, no vacuum lines present, do you know if there is a vacuum manifold located somewhere that these electrics might control? I don’t have much MB experience here, just trying to help a senior friend. I may be over my head.
The one post I read sounded like there was some sort of manifold type device. I’m not sure about MB, but on North American cars, the vacuum hoses are usually brightly coloured.
I took the car to an independent MB specialist and he scanned the system for me. No codes were found for anything relating to my issue, just some old codes for low Freon and failed compressor which he cleared. He said not every component that could fail would throw a code. He said that the only true way to tell was to pull the entire heater box and ductwork to access all of the vacuum motors and electric blend door actuators for individual testing. He quoted 12-hours at $120 an hour and that is only for diagnosis. Parts would be extra. No estimate was given for parts since it is not known what is needed. He charge me 1-hour for the scanning, $120.00. Now here is the kicker, when it went in there was NO action from the default position of defrost and floor. I now have SOME change of airflow from defroster to center and side vents and back to defroster consistently. I’m just going to go with it for now and see what develops or fails again. I’ll post any changes/results as they occur.
The CCU display has the ability to display HVAC codes and other useful information. I know that this capability is there, but you will need a detailed service manual, maybe a factory service manual, to get the instructions on using it. That car might now be old enough that online FSM’s are available at MBUSA.com.
Hope this helps,
Thank you for the help and your Service to our Country. I found this video AFTER I spent money for the fruitless diagnosis. I was hasty.
The gentleman shows how to read the codes and even displays a list of the codes at the end of the video.
I’ll keep playing with it for now. Be well!
I was in the U.S. Navy Seabees 1972-1978 MCB-6 and MCB-20. Equipment Operator (EO) and Equipment Mechanic (EM) I carried 2-rates.Good show! Glad you found the video. The internet and YouTube are a wonderful thing.
I trained as Nike Hercules Missile, Launcher and Warhead repairman. Spent a year at that before OJT into HAWK Fire Control System Repair.
You can access some of the vacuum lines and actuators from behind/under the glove box, but to really tackle this issue the dashboard needs to come out. The rubber bellows inside the vent door actuators love to leak. You may have noticed the vents respond under large engine vacuum, such as decelerating off the highway. The recirculate door actuator up by the windshield on the passenger side is a common failure. I plugged the vacuum line for it on my 96 C220 since I didn’t have a replacement part and was fine with leaving the recirc door closed all the time, now everything else works perfect. Many of the actuators share vacuum lines with each other, which is why usually it only takes one or two bad bellows to render the rest inoperable. Testing the bellows is easy once you gain access to them, either with a vacuum pump or I just blew into them to see if they held air or leaked.
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