1990 300E blower motor not working - PeachParts Mercedes-Benz Forum

BillsMerc.shop · #1 05-07-2008, 01:23 PM

The blower motor stop working so I pulled out the blower, not all that bad of a job. I bench tested and oil the motor it works fine. Until I put it back in the car. Could the switch or the blower regulator be bad and how do I test each one to figure out were my problem begins?

Arthur Dalton · #2 05-07-2008, 01:50 PM

The red is always HOT on the blower, so if you ground the blu wire at the blower and get full fan, the reg is bad or you have no trigger voltage to the regulator [ yellow wire should have 2-9v, depending on speed selection at Panel.]
If no 12V at red , you have a bad strip fuse

865sp300e · #3 05-07-2008, 01:55 PM

Check the blower fuse, its the big black plastic (2" long) on the left front strut tower with thick wires. You see a metal strip fuse when you open it.

phiberoptic · #4 07-28-2008, 04:45 PM

Quote:

Originally Posted by 865sp300e

Check the blower fuse, its the big black plastic (2" long) on the left front strut tower with thick wires. You see a metal strip fuse when you open it.

I have a 1993 300e. The blower just quit working last week and it's in the 90's here in NC.

I was just about to call the dealer today to set up an appointment to take it in, when I decided to check the web just for ha-ha's. I checked fuses, tapped on relays, took out the climate control unit and checked the wiring/buttons.

We are only planning to keep it another year before my wife and I move north to PA. I think it knows somehow...and has been acting up. In the last 3 months it's needed a smog pump , idler pulley and serpentine. 2 days back from the shop for that and the radiator blows. 4 new tires to get thru inspection for another year. And now the fan quits on me. GRRRRRrrrrrrr.

Anyway, I was lurking on here and read this fix. I checked the fuse on the strut as you suggested (what the heck a fuse is doing there I'll never know) and at first glance it looked fine. I was about to close the fuse cover, when I looked at it one more time a bit closer and thought I saw a crack. I pressed on it with a screwdriver and sure enough, the fuse was blown. I turned on the ignition, bridged it with a screwdriver and abracadabra! my fan was blowing!

Looks like a $2 fuse will fix it!

I registered just to say THANKS!

Your post saved me a visit to the dealer and from putting more money in a car that's become a money pit.

You've earned five Karma Points for this one bro.

Mark M · #5 08-21-2008, 06:11 PM

I have a similar problem but with enough varaitions to make it interesting:

1990 300te - 145,000 mi
Yesterday my blower also stopped working when I pressed the button to change the fan speed. Cleaned all fuses, replaced 30 amp strip fuse. Took apart blower housing and disconnected red (hot) and blue (ground) wires from blower motor. Before I removed the blower, I thought I'd test it one last time, so bridged the two wires and all speeds worked fine. Re-assembled all and it worked until today when I pressed the button to change the fan speed. All dead again.

I thought maybe disconnecting the power source would reset the system, so I disconnected the battery. Still dead. Fuses are all still good.

I am now totally baffled, and getting hot without AC. The only two components I can think of checking are the blower regulator and the fan speed switches in the dash. Any quick way to test before I start tearing the car apart again?

Arthur Dalton · #6 08-21-2008, 06:22 PM

The test are made at the 3 wire connector behind the brake booster......Rd/Bk/Yl

R to B -12V
Y to B - 2-8 V , depending on fan setting.

If No R to B , feed is bad .. [ fuse /ign sw]

If Y to B is NO, then CCP is bad or fuse for panel.

If both test are YES , then the reg is bad or brushes in motor are going.

Test for motor is to ground the blu wire ...that gives full fan
If NO , motor is bad ..if Yes , reg is not grounding/regulating b/c it is bad or is not getting trigger variable V from Panel [ yl wire]

Mark M · #7 08-21-2008, 06:50 PM

Arthr,

Thanks for the testing summary. Of all the posts I searched on this and other sites, nobody presented the layout for troubleshooting as you have.

I will test immeditely and post the results.

Thanks,

Mark

Arthur Dalton · #8 08-21-2008, 06:53 PM

Just check the Archieves ..I have posted that primary test a hundred times.
The search thing can be hard if you don't have the exact words ...
I should put most of the common test I use all together under some sort of Electical diagnosis format someday.

Mark M · #9 08-21-2008, 07:17 PM

Arthur,

When I check the archives with the correct key words, I do see that you have posted quite extensively on the blower regulator topic. My bad.

The results of my test with a voltmeter are as follows:

Red to Black 12v
Yellow to Black: low fan speed 1.25 v
mid fan speed 4.92v
high fan speed 7.61v

So all inside switches are good and the problem lies with the blower motor or blower regulator. The interesting thing is that when I accessed them before and pulled the red and blue wires off and then put them back on, the system worked fine before it went out today.

Is it typical behavior for a bad regulator to be an intermittent problem or do they tend to go all at once?

Arthur Dalton · #10 08-21-2008, 07:27 PM

OK

You now want to just run a jumper wire from the blu at motor to a good ground w/key ON.
That should start fan on High speed. This is just a regulator by-pass test. If NO , then spin the fan by hand as you have this jumper wire hooked up...if YES w/hand spin, then you have some brushes hanging up due to wear/dirt . etc ...
Sometimes you can clean them up.......

If fan comes ON w/jumper , reg is suspect...but before condemning regulator, peal back the Yl and take a V reading down there at reg. just to make sure you don't have an open wire from /between the 3 wire plug to the regulator.

As you can see , the regulator controls the NEGATIVE side of the circuit [ a SWITCHED GROUND circuit], so the jumper takes the reg out of the circuit for testing purposes..but don't forget , NO trigger V at yl of regulator and you will get NO FAN b/c the reg is not being triggered....it needs that variable V to regulate the ground side of the motor.

Mark M · #11 08-21-2008, 07:36 PM

I suspect that the regulator is bad since when I had it apart before and grounded the blue connection and the fan ran full speed right away.

I will perform those final tests later tonight or tomorrow AM. Will post results then. Thanks again.

Arthur Dalton · #12 08-21-2008, 07:40 PM

OK

Just remember .. when you have an intermittant fan, it is more likely the brushes than the regulator.
So, the best test are if you can catch it in the NO FAN condition when doing the test. A few lght taps on the motor is sometimes all that is needed when a brush is suspect of not making a good contact.

Mark M · #13 08-21-2008, 07:54 PM

If when I open things up, it all works fine again, can I bench test the regulator?

What should the readings be off the blue (ground) wire from the regulator?

Arthur Dalton · #14 08-21-2008, 08:13 PM

Bench test of reg will require Var V trigger ...you have Var power input for that at your bench?

The reason my test are In SITU is b/c we are concerned with the circuit LOAD conditions present as they are in the car. That is why you should have just jumpered the blu wire from the get-go instead of pulling the motor for a bench testing.
Lets do the test........in the order I post, please.

Mark M · #15 08-22-2008, 11:56 AM

Arthur,

As you suggested, I ran a jumper wire from the blue at motor to a good ground w/key ON. No fan. After rotating the fan by hand a couple of times, it kicked on. Reconnected the blue wire and all speeds work.

It looks like your hunch was correct that with an intermittant fan, it is more likely the brushes than the regulator. I will order the part, install and report back.

Mark