Unusual HVAC issue
 

My ‘08 R320 CDI has started doing something very odd...

I replaced the battery under the pass seat and now the hvac blows hot HOT air through defrost no matter the hvac controls are set at. I can have it in auto, off, floor, a/c, etc. the motor just stays on. It’ll start doing it about three seconds after you turn the car on, either running or not. It is NOT doing the more usual fault of blower motor running with the car off.

The only other thing I’ve done is spend three days cleaning puke out of my car from an extremely intoxicated passenger. That involved removing the pass seat( replaced batt at that time since it needed it) and taking most of the console apart. FYI: yellow curry stains carpet.

Perhaps I got something wet while cleaning, I’m not familiar enough with the R-class to know where the blower/hvac modules live. But I’m my experience with older MB’s, the only real thing living under the console is the abs sensor.

I also had the car running after the batt install so I could run the heat while working on the puke in the cold. I don’t recall it acting up at that time.

Any ideas? Or at least some wiring diagrams.

Thanks

I have no experience or knowledge of the R class or anything from it's era, but are you sure you didn't accidentally pull something loose when you were de-puking the console? If you put extra strain on a wiring harness or partially pulled a plug apart, it could certainly cause unexpected issues. Retrace your steps and see if there's something that may have been pulled or inadvertently filled with sick.

Oops... by abs sensor I meant airbag sensor.

Anyways, the only thing in that console I unplugged was the cigar lighter. But considering the hvac controls are at the bottom of the “stack”, perhaps I unplugged something from the back of the hvac when sticking the forward part of the top console trim in. As I recall, it gave me some problems.

I didn’t really notice this problem until I got on the highway for a 47 mile trip. Felt like my face was gonna melt, even with the back windows down. Gotta love that hot Mercedes heat lol.

Anyone have a Parts drawing/catalog link? I need to order a couple trim fasteners that I broke the first time around.

Step one is to stop picking up drunks on the road.

The default for an automotive HVAC system is heat / defrost. I have seen various micro-controller based systems not boot if they have been online for a long time then power is removed or if they have been taken off line and power is applied erratically. ( RE the battery cable is sparked a few times while reconnecting. )

See if the lighter and other fuses are intact, the HVAC will likely have at least two power sources, one for the control and one for the fan.

Next would be to disconnect a battery cable, wait 5 min then cleanly reconnect. If the HVAC doesn't come up at this point, I'd go through this a few times. I had a 800,000 Watt generator controller that was online for an extended period of time that would not reboot until the battery switch was turned on and off a few times.

Well I finally got around to looking at this again.

Removed console parts again, but everything looks good. There is actually no way I could have molested the HVAC wires.

Next I checked ALL the fuses, even ones next to batt under the seat.

Then I removed a batt cable with no change.

Lastly I tried a few different hvac reset procedures I found via google.

I guess a trip to the dealer is next. Unless I buy another hvac push button thing off ebay. But I'm not sure if that thing is where the brains of the hvac system live or not.

Anyone know how to remove the hvac control?

Where are people getting wiring diagrams these days? I think the Russian site is long gone if I recall.

Wiring diagrams?? Does nobody know where to get them these days????
Anyone?

Get a copy of the FSM. Ebay is your friend.