I have a ML 320 and one fine day the AC suddenly began blowing HOT air - it was as if the heater was set to ON even though the I set the AC to ON and used the lowest temperature... tried all possible AC settings but to no avail..

I took it to the local MB dealer who said that there was loose electrical connection and "fixed" it.

After a few days again same problem and another trip to the same dealer. This time they said it was blown fuse, replaced it and claimed it was fixed.

After a few days again same problem and the dealer said it could be a control module problem. Replaced it, checked the fuse but the AC continues to blow HOT air. They now say it could be the stepper motor that controls the front vent flapper and is asking me to cough up $1500 for fixing it.

Should I trust the MB, pay the $1500 and get it fixed? I really feel that there is some funky electrical problem because now the the engine light is coming ON and the engine seems to be misfiring. Dealer says it is some electrical problem and another $800 to fix it.

Has anyone faced the "hot air" blowing from AC problem? Any comments and suggestionswould bev. appreciated.

 

I have one of the first ML320s off the line, original owner. Unfortunately, we too serviced it up until the last year with the dealer, and this dealer is in Montgomery right down the road from the factory. All I can say is your experience is "classic", everytime you go in the diagnosis is different. Thank the Lord God I have found a local mechanic willing to work through the issues, he just fixed my oxygen sensor problem the dealer wanted $450, he fixed it for $70.

Find a good local mechanic it will be well worth the effort. Let me know if you are in central Alabama.

 

Sounds like a short to ground some where- possible also a loose ground causing a spike of some kind blowing fuses. fuses don't go bad and blow for no reason. have your mechanic check the heater control valve- if the valve stays open the hot coolant is working against the a/c coils and 180 degree coolant will beat out 60 degree coils any day.

 

Mine did that and it turned out to be a short in one of the blower motors, I have experienced the same problems with dealers. They charge 4 times what any other mechanic would and can't keep their stories, err diagnosis, straight. They charged $6000 to replace the computers on my V12 SL and then when it did the same thing a month later they wanted to have me give them another chance to diagnose the problem. I changed the batteries in the keys and it has worked fine since. $6 instead of $6k. I would love to find a dependable mechanic in my area (Bakersfield, Ca) if anyone knows of one.