Heater blower resistor failing

[Shutz]

Hi. I have just registered as I am a new owner of a Mercedes. Never had one before. Very exciting.

I am pretty mechanical so can do just about anything if I’m pointed in the right direction.

the front heater blower will only work on ‘5’ which I identified as the heater blower resistor. I changed this for a new after market part and it has blown again within 2 weeks. It may be the after market part as I’m not sure on the rating of the thermal fuse which is the usual cause for failing.

can anyone shed any light on possible reasons for this failing again so soon for me to investigate.

I have a few other issue but I’ll stay with this as it’s winter.
Thank you

 

[wrdcc01]

Could very well be the blower motor is going faulty, can you get hold of a DC clamp meter as it will show you if the current draw is getting too much for the resistor pack to cope with. Should that not be an issue then an OEM resistor is the order of the day.

 

[Shutz]

Could very well be the blower motor is going faulty, can you get hold of a DC clamp meter as it will show you if the current draw is getting too much for the resistor pack to cope with. Should that not be an issue then an OEM resistor is the order of the day.

Thanks for this info. My brother in law works for Audi so getting equipment isn’t a problem. I still have the oem resistor and thought about swapping out thermal fuse with a new one. It does seem that it has failed on that after testing continuity

 

[Oskar13]

If the thermal fuse is blowing it’s probably your fan motor that’s causing the problem.

 

[Shutz]

Hi. Thanks for the help. Haven’t had a chance to reply until now. I was short on time getting around to resolving this. A few weeks ago whilst picking up the shopping the motor started to sound rough. Sounded like the bearings had failed.
Order a new motor from Mercedes which was surprisingly cheaper than aftermarket. Only took half hour to swap out. I had a 92’c micro thermal fuse. Much lower rating than the oem at 167’c. Thought I’d give it a try as I had no others. But it has been in and working daily for around 4 weeks now I think.
So yes it was the motor drawing too much and overheating the resistor coils.
Overall a good experience with my 1st Mercedes.