I did a search and cound't come up with any clear answers to my typical blower motor problems..

it hasn't been working for a while. could be a problem in the winter with defrosting the windshield so i start to work on it today.

1. check fuse #11. looks fine.

2. took out the blower motor. hooked it up directly to battery and it ran. so i ruled out the brushes.

3. plug it back in and let it hang down while i try to put the fan on. the fan kicked on. stayed for a couple of seconds and turned back off. i then pushed all the buttons and turned up/down the temp setting. it kicked on and off at random intervals for a while. then it stopped that.

4. I thought it was the HVAC controller. and think it might need to be resoldered.

5. before i took it apart i pushed it a couple more times and i notice everytime i push anything but "o" (off) there is a humming/ringing behind the dash.

seeing from number 5 i was thinking the controls do work, but maybe there is another component at failure causing to power to the motors? any input would be appreciated.

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198? 300D ???K - Future DD
1989 300TE 285K - traded in '12
1984 300SD 186K - Sold in 08
1978 300SD 330K - Died in 05

Could be the resistor pack, but I'd bet on brushes -- intermittant operation could easily be worn out brushes not making good contact.

The test is to check for voltage at the blower wires -- if you have voltage and the fan only operates sometimes, it's the fan. If the voltage comes and goes, it's probably the PBCU or fouled resistor pack.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

sounds expensive

i will use a multimeter to check and update tomorrow if it is getting voltage. thanks a lot.

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198? 300D ???K - Future DD
1989 300TE 285K - traded in '12
1984 300SD 186K - Sold in 08
1978 300SD 330K - Died in 05

I've replaced blower moters in my '78 300CD and my '88 560SEL and here's some of what I had to deal with.

Ultimatly both failed due to bearings and/or brushes in the blower motor itself. Both cases, replacing the blower motor fixed the problem. But that doesn't really help you out much... Here's some of the interesting things I saw when troubleshooting.

In BOTH cases, when removed from under the dash and pressing a button to activate the motor, I'd get a hum. While holding the motor (in its housing) in the palm of my hand, if I jerked the motor slightly, it would spin up and blow almost at proper speed. (Also if I were driving 80mph and hit a button which opened the vents on the 300CD it would provide enough airflow over the fan, effectivly kickstarting the motor and the electricity would take over) If I gave the motor (both cases) power and they weren't moving, giving them a little spin caused them to come on. Basically what it boils down to is even if the motor works while out of the dash, it may still be the problem. The best way to test this is the check the voltage in the plug for the blower motor. If voltage is there (I forget the levels) then the motor is probably the problem.

It wouldn't surprise me if you wind up replacing a blower motor since I've had to do the same thing on both of my Mercedes and I've already built into my 560SL budget the $250 to buy a new blower motor for it.

Good Luck and I hope my rambleings help get your car's ACC going like it should!



Scott

Thanks everyone for all the informations. I went onto this job thinking it would just be the brushes so this is quite fustrating.

this is for my W126. I will try to do as suggested and try to spin it while it is humming, and check the voltage through the line.

The fuse on this car was not upgraded and it still has the normal ceremic type fuse. Interesting how Mercedesdr describe how the heat would make the fuse act funky i did not think of this before. how hard is it to do this upgrade? does it involve taking apart the dash or fuse box?

i really only need this for defrosting the windshield since the A/C doesn't work anymore. if i get desperate maybe i will just hook a wire with a toggle switch for a defrosting fan?

will work on it tomorrow and report back.

__________________
198? 300D ???K - Future DD
1989 300TE 285K - traded in '12
1984 300SD 186K - Sold in 08
1978 300SD 330K - Died in 05

Ned, certainly not an expert but in my (now totaled W126) I had the same symtoms and it turned out to be the metalic strip fuse located in the engine bay in its own separate little box. It seemed that although it was broken, when I would go over a bump it would arc enough to get the blower to work. Cheap fix. Just a thought. AJ

So i went down to work on the car again today. i couldn't find the multimeter so i was fiddling around with the HVAC controllers. i noticed that if i would push the fan button in and hold it in the fan would get a kick.but as i let it out it would disconnect again.

so i took the controller out and cleaned all the contacts. and now it works!

i was glad i didn't have to resolder the thing

Thanks for all your help guys. looks like it is either the brush, controller or fuse when it comes to these blower motors.

BTW i saw a brand new blower motor on ebay for $88 if anyone needs one.

__________________
198? 300D ???K - Future DD
1989 300TE 285K - traded in '12
1984 300SD 186K - Sold in 08
1978 300SD 330K - Died in 05