Cabin aircon blower running long after car shut down

1993-Present: C200 CDI, C220 CDI, C270 CDI, C180, C200 Kompressor, C230 Kompressor, C220, C230, C280, C300 C350, CGI & CDI BlueEfficiency variants
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nicholas128
B Class
Posts: 24
Joined: Wed 12 Jun, 2013 1:44 am
Model you own: w204

Cabin aircon blower running long after car shut down

Post by nicholas128 » Tue 03 Jul, 2018 6:10 pm

Hopefully some of you helpful people can assist me in working out what is going on with my 2009 C300. No error codes come up in the scanner and I'm getting no messages on the cluster at all.

Some time after I have turned the engine off and locked the car, I can hear the cabin aircon blower fan under the glovebox running at a low speed. I've confirmed its the blower fan, since I removed the box that sits on top of the battery where the blower sucks air into the car, and I can see the blower running at low speed. Today I went into the garage more than 2 hrs after I had put the car away and noticed that it was running. Unlocking the car did not stop it, but opening the driver's door did. I suspect this fan behaviour was responsible for recently causing my battery voltage to drop low enough that I couldn't start the car without charging battery first. At the time I had put this down to the recent string of cold mornings taking its toll on an aging battery, but now I suspect the fan is discharging the battery during the night. I have never noticed the fan running after turning the car off before. Apparently some MB cars with a fancier three-zone climate control system do use the fan to warm the cabin/reduce moisture when the car is not being used (I think they have a "Rest" button for this), but mine is just a standard climatronic system.

I don't think this fan running so long after the car has "gone to sleep" is normal, but would be very pleased to be corrected. If it is a fault, what are the likely culprits? I think its unlikely to be low battery voltage, since I have charged the battey well and it is now holding a good level of charge. Maybe the blower? The blower resistor?

Your thoughts appreciated.

Cheers,

Nicholas.

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Bartman4800
300 SLR
Posts: 1969
Joined: Fri 10 Oct, 2008 12:10 am
Model you own: w111
Location: Perth WA

Re: Cabin aircon blower running long after car shut down

Post by Bartman4800 » Wed 04 Jul, 2018 9:51 am

I doubt the blower is at fault. It spins when it gets power, that is the only thing it can do.
Neither do blowers stay on because the battery voltage is low.

I suspect you have a relay that stays closed after the power has turned off.
Or someone has been mangling the wire loom.
Look for aftermarket connections (an extra connection on the + pole of the battery going to the firewall)

Most likely there are people here more knowledgeable than me about the C-class


Bart
1963 220 Sb Sedan "Kermit" (Australian Assembly)
1960 220 Sb Sedan "Zum Schlachten" (Early German Assembly, with a torsion bar spring for the bonnet) - Stored in Country WA
1981 Subaru Brumby 1.8 with Weber and 5-speed box "little utie" - Sold to another enthusiast!
2006 Ford Focus "daily driver"
2002 VW Passat V6 30V Station Wagon (SOLD - This car into a money pit)
2011 Kia Sportage "Missus commuter Bus"
2002 Mitsubishi Rosa Bus (converting it to a motor home)

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Ivanerrol
Mercedes Demigod
Posts: 5852
Joined: Sat 12 May, 2007 2:21 pm
Model you own: w204
Location: Melbourne

Re: Cabin aircon blower running long after car shut down

Post by Ivanerrol » Wed 04 Jul, 2018 9:57 am

You might need to visit a stealership or MB independent who has a full blown Star diagnostic system.

I've just had a car with Canbus "issues". Had to get an independent to reprogram. My scanner reset device couldn't do the job.
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nicholas128
B Class
Posts: 24
Joined: Wed 12 Jun, 2013 1:44 am
Model you own: w204

Re: Cabin aircon blower running long after car shut down

Post by nicholas128 » Wed 04 Jul, 2018 7:13 pm

Thanks Bart and Ivan. I will post the outcome once I have figured it out.
Damn, my list of things for the mechanics to address is turning out to be much longer than I had planned... :wall:

Cheers,

Nicholas.

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