A/C Blower Motor
 

My '95 E300D gave me a rude surprise last evening in the 100 degree heat here in Vegas, no A/C. In my case, the fan motor appears to have checked out as the fan does not operate no matter which climate control button is pushed. The fuse is ok, the a/c comp clutch pulls in as it should, the aux fans come on as they should....so do these fan motors just suddenly die with no prior warning or am I missing a hidden fuse or relay that may have knocked the system out?

I am assuming that if the problem is a bad motor that the repair is not going to be pretty as I am sure that it is buried in the most inconvenient spot possible...

Brock

not familiar with your car, but fans usually give some warning, they get slow or make some noise first. try putting in a new fuse. also see if you can get to the fan and apply voltage to it. it may be a control or a speed regulator control box.
John

I would start by checking the plug at the fan and see if it's getting power.
Then check the temperature regulator. It's a metalic box behind the glove box. Pull the connector off and see if any of the pins have power.

Danny

Here's what I've discovered. I have a 1982 300SD. The fan unexpectedly stopped on it. As I repair electronic equipment for a living I thought I'd take a crack at it. I pulled the fan out of the housing below the glovebox. Testing the fan plug revealed that I had 12v coming to the plug with the fan power on max. I ohmed out the fan motor and read 12.81Mohm; essentially an open. I removed the brushes off the motor and discovered severe pitting/scarring of the brush's contact surface. I also discovered that there is an inductor located on the motor board. The inductor actually had a partial break in the solder joint. After resoldering the inductor, despite the pitting/scarring to the contact surface, the fan motor operates quite well now. After the repair, the fan motor ohmed out at 6.2ohms to 13.6ohms.

1982 300SD 262890 miles
1981 500SEL 181922 km

Update
 

Thanks for the replies....here is a update on the problem. This morning I started the car to head to work and the fan came on as usual, yippie!! The climate control unit was set in economy mode. Cool says I and promptly punch the a/c button...a/c comes on! Yippie....but wait....why did the fan suddenly speed up to max and warm air is coming out of the side vent and cold air out of the center vents??? So I turn off the unit (Windows logic....lets re-boot to fix the problem ;> ) and then back on....but then nothing. The fan will no longer function and has given up the ghost once again.

Logic tells me that the climate control box is bad. Looks like rebuilt units can be had for about $260....what y'all think?

Brock

The W124 cars have the HVAC blower motor behind the firewall under the center cowl. That is the first thing to check. Pull it, lube it, check the brushes. http://www.peachparts.com/Wikka/W124BlowerMotor

When you set the head unit to A/C it changes the fan speed to be controlled by interior temperature. So since you had the A/C on a cooler temp than what was ambient in the cabin, the fan switched into max speed to cool it down quickly. Once the temp correlates to the thumb wheel setting, the fan speed will slow down.
Any setting other than Econo is auto fan.

Now the vent air discrepancy may just have been a momentary thing. Did you set the air recirculate switch, to help the cabin cool down? Doesn't sound like monovalve since you have cold air. Plus center vents are always cooler in my W124.

http://www.peachparts.com/Wikka/AcDiags

The fuse for the blower motor on this car is a strip fuse located in a small black box on top of the driver's side wheel well. Is that the fuse you checked?

Those strip fuses, apart from burning out occasionally, after many years of use, also fatigue and tend to develop almost invisible hairline cracks that make them operate intermittently.

Check strip fuse closely!
 

Mine did pretty much same thing - although i never got warm air out side and cold in center...and mines a 87. In mornings (when I didnt need AC) it worked fine. Then in middle of hot day, blower wouldnt come on.

I checked that strip fuse 1st, but was thinking since it worked intermittently, how the heck does a fuse cause that?@

Well, it turned out the screws holding stip fuse to contacts werent making good contact. New strip fuse, old bolts.

Long story short (literally!), short a wire to momentarily bypass strip fuse across 2 bolt heads. See if that gives new life.

On a whim, you may want to check the vacuum lines to your enviromental controls. I've had other vehicles that lost all or part of the vacuum to the enviromentals and had problems simialar to what you are describing. The vacuum controls CAN also mimic the failure of the control box.

Well....it was the fuse I checked after reading your reply....:). And sure enough it looked OK when I opened the cover, but looked as pictured below when I pressed lightly on it.

After rigging a temporary replacement, everything is working as it should. Thanks for the input.

Brock

Beeeeeeeautiful.

Bet you were grinning ear to ear when you found out you didnt need to dig out that blower motor.

I was actually pulling out the whole ACC and stickin it in the refrig at work since I was convinced it was somehow related to temp inside the car. Ppl think Im crazy. Evn ordered another ACC for $400. Then I decided to look more closely at the strip fuse...needless to say, beers were cracked that day. Lucky enough to return new ACC, too.