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1991 300D 2.5 TD
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19 Posts
Discussion Starter · #1 ·
Lately it seems as though my car is spiting me. We recently received some snow this weekend and my blower decided to not work. At highway speeds heat comes out. I pounded on the instrument panel out of frustration to no avail. The blue fuse under the hood is fine. What's the deal?
 

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1990 Mercedes Benz 300E
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1,336 Posts
The fan speed controller is hooked up to the speed sensor in your speedometer. If you are getting air movement at hwy speed but no fan at idle I would suspect that the speed controller is likely faulty.

In my estimation, pounding on something out of frustration usually does more harm than good. Its not a vending machine!
 

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1990 300E 2.6
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182 Posts
Using a volt meter on the strip fuse I put negative to the strut nut and positive to each of the screws and I see 11.9 Volts. I assume that fuse is ok???

What else might cause my heater fan to not work? I just had a voltage regulator replaced, the heater fan didn't work yesterday on way home but also the battery wasn't getting a charge. Now that battery is getting charge the fan still won't come on. Both symptoms showed up at same time. Maybe my OVP is gone too??? I haven't noticed any symptoms to say OVP other than the fan. What else would stop working if the OVP is bad or what else causes the heater fan to not work. Its too cold now to use the car without heat.
 

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W124 Moderator
86 190E 2.3L 16V, 95 320TE 02 S500
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13,288 Posts
Assuming all your fuses are good, either the blower motor is toast or the blower motor regulator has gone. There is a nice R/R link for the blower motor in the DIY section. The regulator lives under the blower motor. Your OVP has no play in the blower motor operation.

Good Luck,

Jayare
 

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1991 300D 2.5 TD
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19 Posts
Discussion Starter · #8 ·
30 amp fuse online and week-long wait: 60 cents
30 amp fuse at the MB dealership: $2.50
Being impatient and buying the fuse at the dealership for instant gratification: priceless
(Plus, I got a free coffee, too)
 

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16 Posts
Heater Blower operation in question.??

Assuming all your fuses are good, either the blower motor is toast or the blower motor regulator has gone. There is a nice R/R link for the blower motor in the DIY section. The regulator lives under the blower motor. Your OVP has no play in the blower motor operation.

Good Luck,

Jayare
Can anyone direct me to links for more information? Fuseable link appears ok. I removed it and am reinstalling it. Will test with volt meter today. Any help we be greatly appreciated!
 

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1995 E320 Sedan, Auto 3.2L w/132k mi.
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162 Posts
...30 amp fuse at the MB dealership: $2.50
Being impatient and buying the fuse at the dealership for instant gratification: priceless...
Heck if i was drivin it frequently I woulda paid $10 for instant gratification vice waiting (inconvenienced) a week....:D

Good post, first time I've heard/read about this fuse link. I'm getting smarter each time I get on here and read.
 

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1990 300E 2.6
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182 Posts
At this age it is likely the brushes are worn. Have you been hearing crickets lately when running the fan? Try slapping the carpet area below the stereo, a good hard slap on passenger side using right hand while sitting in driver seat used to get mine spinning for a couple weeks until I replaced the motor. Need to remove the wiper blade first then keep going down until you reach the motor. Not that difficult.

PeachPartsWiki: Blower Motor Removal
 

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1993 400E
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4 Posts
Relates question about resistor/regulator.

I'm having problem with my blower system also. Tore it down to the blower today. Bench tested the blower...works fine. Testing the wires to the blower shows I'm getting power through the positive (red) wire, but nothing through the ground (blue).
My question is, does the resistor and or relay operate through the ground circuit? If I bypass everything by running a ground wire directly to blower, it runs high speed, but I have no control from the inside dash controls.
'93 w124 400E.
 

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1993 400E
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4 Posts
ok, further investigation answered my question. The resistor DOES operative thru the negative side. Red wire is positive (gets redirected to blower directly from resistor terminal).
Black wire is negative into resistor, blue wire is negative out to blower. And i assume the yellow wire is variable voltage into resistor.
Does anybody know the values I should get when I run voltage and continuity tests thru resistor? I'm getting -0- resistance between the black & yellow terminals. That doesn't seem correct.
 

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Premium Member
2016 E350 wagon; 1994 E320 wagon
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8,002 Posts
use a couple jumper wires of decent enough gauge to carry 30 amps, and jumper 12V directly across the motor. make sure that motor is securely strapped down to your bench before doing this as the startup torque is likely enough to make a motor sitting on the table spin around causing you to short out your jumper wires
 

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1987 300e (W124) - 223K miles, 1995 C280 (W202) - 250K miles Sold
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226 Posts
Let's assume for a moment that the blower motor and regulator are OK. Look at where the wiring comes out of the top of the box where the blower motor is located. They come out on the left/driver's side. Follow them to a terminal block located on the firewall near the power brake vacuum booster. One should be ground/earth. One should have +12V. The last one should have around +6V; the exact voltage will vary depending on the fan switch setting. If any of these are wrong, check for connection problems. If the control voltage never appears, the regulator will never turn on the fan. This control voltage is coming from the climate control unit on the dash. That unit could be faulty; I've replaced mine with one from a junkyard and most of its functions are OK as far as I can tell. My heater has other problems; some flaps don't open/close as they should. I plan to replace the vacuum switch block and see if that helps. It might not be opening/closing vacuum lines correctly in response to signals from the CCU. If that doesn't help, I'll try to get a better CCU. New ones are pricey so I'll look for one that's tested and guaranteed working.
 

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1987 300e (W124) - 223K miles, 1995 C280 (W202) - 250K miles Sold
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226 Posts
Lest anyone suggest replacing some or all of the vacuum pods under the dash...I've already replaced all of them with new ones and verified that they all work properly when the get/lose vacuum! I wasn't about to put the dash cover back on before making sure of that; it's a lot of work top remove and replace the dash cover. I put in one from a junkyard that was in excellent condition (no cracks) which I painted the correct color (Shadow Blue). It looks 1000% better than the one that was in the car when I bought it.
 
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