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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53904
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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I have a 2002 Mercedes ML320. The A/C won't come on. The

Customer Question

I have a 2002 Mercedes ML320. The A/C won't come on. The heat is always on and it won't switch over from heat to A/c. Even when you turn the temperature down all the way heat still comes in.
Submitted: 2 years ago.
Category: Mercedes
Expert:  Marty replied 2 years ago.
Hi, assuming that the a/c compressor is working and the system is full of refrigerant the most likely fault would be a bad temperature blend door actuator. If the actuator fails the system will be stuck in heat mode. The actuator is mounted on top of the heater housing. The instrument panel will need to be removed to replace the actuator. Approximate cost of this repair is $850.
Let me know if you have any questions.
Customer: replied 2 years ago.
Is it possible that it might be the HVAC contro module? How would you distinguish if it's not the actuator itself but the module that controls it? My daughter took it to a Mercedes dealer ( that I don't particularly trust and that said this: HVAC-control module: A?C control module internally faulty actuating hot/cold blend door and erratically actuating blower motor speeds. Need to start with module. My problem with their diagnosis is that it seems like if I was to spend $2000 to have a new module put in that might not be the problem and I might still have to put in a blend door. What would you suggest?
Expert:  Marty replied 2 years ago.
Yes it is possible that the module is at fault but I question the extent of their diagnosis. A lot of techs spend very little time on the actual diagnosis. They just replace parts and move on to the next one if it doesn't fix it. If you notice that the blower is also erratic as they stated you might indeed have a faulty module. If the module doesn't fix anything they should not leave it in the car. It might be a good idea to seek a second diagnosis from a reputable independent Mercedes technician.
Let me know if you need anything else.