Climate control unresponsive
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Junior Member
Joined: Aug 2010
Posts: 38
Likes: 3
slk 230
Climate control unresponsive
Hello everyone, have a strange problem. The climate control unit in my 08 ML550 continuously blows hot air to the front defrosters only. And only hot air. Fan speed stays constant. You can press buttons and they light up, even fan speed goes up and down when pressed but does not change speed Vent selection inop but light up on button. But nothing changes or moves. Stays blowing heat at defroster even when unit power pressed off. Bought a new climate unit from Benz, installed and exact same thing so its not the head unit and Mercedes took the part back. Whew. The Mercedes guys wanted to tear dash out to diagnose, $1,000 labor. no way is this a wire issue under dash. Plugged computer into it has non communication codes for like 8 climate operations. From the flap actuators to blower control, to blend actuators. I feel as if this must be a SAM unit failure somewhere and the control unit cannot communicate with the items it needs to to give directions. Anyone ever seen anything like this before? Pulled a wiring diagram and it kind of pointed me in the direction of the battery compartment fuse block. It seems like there is a hot wire from all the blend door actuators and blower fan that go into this block. Any input would be greatly appreciated! Thanks in advance.
Thread Starter
Junior Member
Joined: Aug 2010
Posts: 38
Likes: 3
slk 230
Thanks Dundee, it is a 2008 ML550 with only 83k on it. what a truck to drive, amazing difference over the V6 in the ML350. Just cooks you like a chicken because of this problem. The vin number is 4JGBB72E58A406152 The codes there a fresh. Did a complete scan and cleared all codes. These are the codes that came right back.
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Thread Starter
Junior Member
Joined: Aug 2010
Posts: 38
Likes: 3
slk 230
Replying to my own post. This problem fixed!!! The problem was the blower motor resistor/controller is part of the LIN system that controls all the air vent actuators. After looking at electrical diagrams I realized this. Swapped in a known good blower/resistor unit and the problem was solved! Takes less than an hour to do this job. The Mercedes dealer wanted to tear the dash out to look for a bad plug or broken wires at one of the actuators. Quoted me $1,000 just to make the attempt to fix and flat out said they could not even guarantee that would even be the fix. Just ordered a good used unit for $110. Whew. I hope this may help anyone in the future that may run across this goofy problem. Good luck all.
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