Hello everyone, I'm new to the forum.
My 2007 S-Class heater is only blowing cool air. AC worked fine during summer but now that it's getting colder outside, my heater is only blowing cool air. Please Help

 

Check the heater control valve near the drivers side firewall. For a car of this age if this hasn't been changed you should change it because it will fail (plastic falls apart).

 

I am having the same problem with my 2008 S550. I researched this issue online and probably is the Heater Control Valve. But was urged to check the fuse first and see if it's blown. If so, try replacing the fuse first and see if it doesn't fail. The commenter said he got two more years out of his Heater Control Valve without any more blown fuses. My question is: where the heck is that fuse located ? I checked the fuse chart and the only thing I could find was a 20 amp heater fuse located in the right side dashboard at position 90. I opened up the fuse panel and there was no fuse in that position. I put in a fuse but it didn't do anything. Also didn't blow. I'm wondering if there is a different location for the Heater Control Valve fuse ? Anybody know ?

 

Check heating system shutoff valve at engine, controlled by engine control module – part # 2308300084.

 

The problem with this strategy is that the heater control valve is made out off plastic and can break apart while you are driving because the plastic is old an brittle which means all of the coolant is going too stream out of the car. It's a $50-$60 dollar part that's easy to replace, why not do it for peace of mind?

 

Thanks ! Good advice !!

 

I know this is an old thread, but I thought I'd add to it rather than starting a whole new one.

My heater was blowing cold air. Given the issues I've had with the A/C as well, I have long suspected the heater control valve. I went ahead and ordered one for roughly $40 or so. Saturday morning I went to work. I didn't have to remove the wipers or the panel under them. The old valve came out in two pieces, the top fitting snapped off and crumbled when I tried to remove it from the hose. Obviously this is a limited life part!! The new one went in without issues. Took me less than an hour and coolant loss was maybe half a cup or so. No big deal. I took apart the old valve and found that there was some debris in the pinion gear that prevented it from moving the valve slider up and down, which confirmed that the old valve was indeed bad.

Unfortunately, the heater was STILL blowing cold air!! That was an unwelcome discovery. So I connected the laptop and started up DAS. Using actuations I was able to confirm that I could get nice warm air blowing from various places. I ran the actuator teach-in, followed by the normalization routine. This is used to let the control unit "learn" the actuator and valve positions after something is replaced. In my experience with this car, it seems that this kind of data is occasionally just "forgotten" and various stuff stops working right. For instance, there's also a teach-in for the vent controls; I had to do that once because one of them wasn't working. Anyway, after doing the teach-in and normalization, the heat seems to be working now. Sometimes it seems like it's not, because you'll get "not very warm" air flow from a vent, but then you'll feel warm air from somewhere else... it seems like the heating system simply works differently on this car from what one may be used to, which is "Car blows hot air in varying quantities to keep the temperature at the set point". This one seems to be more "Car blows hot, warm, or sometimes even cool air as it thinks is needed". Either that, or it's not really fixed! I'll know more after we've had the car on the road more. It's 23 degrees F and there's snow on the ground today, so it should be a good day to test the heat.

This kind of stuff is why I say that if you're going to own one of these, either spend a few hundred bucks on a laptop, adapter and XENTRY/DAS, or be prepared to spend a whole lot of money on shop time. An OBD scanner won't cut it... when something like this happens, you're not going to fix it without DAS.

 

Did you check that your footwell settings are set to the actual climate control temp? The footwells can be set 2 degrees cooler, or 2 degrees warmer. Also, make sure the airflow is set to focused to get the proper air distribution from the main vents.

 

Really, none of that matters when the system is only blowing cold air. I'm talking about a 35 degree day (Fahrenheit, not Celsius, so it's cold not hot outside), temperature controls inside the car set for HI, and cold air blowing out the vents. I don't care what the footwell or air flow settings are, you should be getting warm or hot air from somewhere. Even the defroster was blowing cold air.

I don't know for certain about all of the HVAC system flaps and valves, but I do know that the heater control valve I replaced is an open-loop system. It's nothing more than a motor driving an actuator with a worm drive, with no feedback as to its position. It's a cheap and simple solution, but there are trade-offs. In cases like this, the usual approach taken by designers is to include motor current sensing in the design. You drive the motor in one direction until a current spike indicates a stalled motor and the end of its travel, then drive it in the other direction to find the opposite travel limit. Once you know the time required to run from one travel limit to the other, you can interpolate locations in between. There are problem with this approach, of course. If a part is replaced, you don't know that it's in the same position that you think it is. It may also move with more or less speed than the old part. On top of that, your control system may "forget" its position entirely for various reasons, and then there's just plain drift -- your calculation of an actuator's position is not always accurate. This is why you have the "teach-in" and normalization routines in DAS, to find the travel limits for each actuator and get everyone back on the same page.

In my case, I know the old valve had some debris jamming the rack and pinion that drives the valve slider. I suspect that made the control unit think it was all the way open or closed when in fact it was just jammed near one end of its travel. Running the teach-in and normalization routines allows the controller to figure out what the valve's actual position was, and correctly control the flow of coolant from the engine through the heater core. I drove it a while last night while I was out running errands, and everything worked great. I now have the footwell temperature set to +1 and diffused airflow, by the way -- but early in the troubleshooting process I had tried other settings.

 

Hello Dale,

unfortunately am having a similar issues as I have changed every part in the cooling system and still I get no heat at all.