A/C blower not working

[rjk]

'88 300TE

Before I start pulling things apart, here are my symptoms. A/C/heater blower is inoperable, no matter what setting I select on the fan speed control nor on the system selector. I get heat/cooling flowing through the vents when at speed and the air pressure is pushing it through so the basic system seems to be working, just no blower. It had worked intermittently for a period of a few months (worked when temps were moderate but not in extremes of hot/cold) but now there is nothing.

I figure a bad connection or solder joint somewhere, probably on the switch board, has finally broken. Am I on the right track? Is there a relay I should be checking first? I am not looking forward to pulling the switch board out of the console.

Thanks in advance...


'89 560SL (wifemobile)
'88 300TE (my commuter, for sale)
'94 945T (daughter co-opted it for college, used to be mine)
'99 S80 (mom-in-law's)
'88 240DL (son's)
'84 242Ti (future commuter)
'68 GT500KR (under restoration)
--
Bob K

[lee polowczuk]

did you check the external fuse on the drivers side just in front of the master cylinder?

it's in its own black rectangular box.

[1991300SEL]

I'll suggest the simple stuff.

1. Fuse box under hood - check #5 fuse
2. Strip fuse not far from fuse box. If my memory is on, it's within a small cylindrically shaped plastic tube. It's a 30 amp fuse - might be blown

How are the motor burshes looking?

[rjk]

All the fuses check out. Don't think it is a fusing issue since compressor clutch kicks in. Just the blower doesn't run. I'll check motor brushes this PM.

[R1990]

Just went through this ordeal with my R129 but should be similar to yours. Process of elimination but you need to know where to start so here's your starting point. Your problem is most likely the blower resistor. The resistor is located very near the blower itself and is bolten down to a heat sink. Before you start buying parts, take out the blower assembly and test the blower without the resistor. If the blower works, then you can rule it out as the culprit. Next test the blower and resistor. If the blower doesn't turn on, then you know that the resistor is the problem. The problem is that the resistor is often more expensive than the blower itself. Hope this helps.

[Arthur Dalton]

Earlier blower used speed resistor.. this chassis has a transistor regulator circuit.
Before going to blower/reg , check for voltage at 3 wire plug at firewall, behind booster
red to blk is bat 12v. Yellow to blk is 2-8 v. depending on panel setting Set at defrost for this test

..if no 12v , you have a bad fuse/wire feed . If you have proper vlotages , THEN go to the trouble of getting to blower/reg.
Once there , ground the blu wire on the blower . if blower starts , reg is kaput.

[jcyuhn]

Quite possibly worn brushes on the blower motor. When they get short enough, they can jam sideways in their housing and the springs cannot push them against the armature (is that the right part name?). Pull the motor, visually inspect it, and test with a straight 12v.

Suppose it could be the transistorized speed controller, but I've not heard of those going intermittent before failing.

- JimY

[Robert W. Roe]

how hard is it to get to the blower / regulator?

My 91 300TE is having similar problems... no fan on any pushbutton position.

And the part about grounding the blue wire, do I disconnect it from whatever it's connected to or ground both ends?

Thanks, Bob

[jcyuhn]

The blower is hidden directly below the windshield wiper motor. You have to pull the wiper to access it. Surprisingly, it's not a bad job. Remove a bunch of trim in the area, four bolts to pull the wiper, and you are at the blower. Helps a bunch to have the shop manual for this one. About 45 minutes for a first timer DIY should get you to the blower motor.

Don't know about Arthur's blue wire, perhaps he'll chime back in.

- JimY

[Arthur Dalton]

Let me explain the blu wire test in detail.
The blower motor has 12 v. POS + to it all the time [ with key on]
So, on the other end of the blower is the GROUND side [ usually a blu wire ]
This wire goes to the REGULATOR , which , when recieving trigger voltage from the control panel and operating correctly, completes the ground cicruit
[ this is refered to in the business as a "SWITCHED GROUND," meaning the on/off operation is switched on the ground side of the circuit instead of the normal hot side of the circuit. ]
So, if one was to hook a wire to the ground of the chassis [ or neg. bat ]and touch it to the ground side of the blower [ blu wire going from blower to the reg], he is simply eliminating[jumping] the REG out of the circuit. Doing so also eliminates the variable speeds of the blower cuz that is what the regulators function is. So, you now have direct bat voltage to the blower .
You will see many postings here recommending one to take the blower out and hook it to a bat , direct 12v , etc.....not needed with this simple test

.. touching the blu wire to ground does this without removing anything. It is just a quick test to verify blower and diagnose Reg...
.. this is always the second test... the first test is the connector behind the booster for voltage verification from the control panel before pulling the firewall apart for nothing....
Just remember this .. the regulator is at the very end of the complete circuit, so one wants to verify voltage feed before just jumping on the reg ..

[Robert W. Roe]

Originally Posted by Arthur Dalton

Let me explain the blu wire test in detail.
The blower motor has 12 v. POS + to it all the time [ with key on]
So, on the other end of the blower is the GROUND side [ usually a blu wire ]
This wire goes to the REGULATOR , which , when recieving trigger voltage from the control panel and operating correctly, completes the ground cicruit
[ this is refered to in the business as a "SWITCHED GROUND," meaning the on/off operation is switched on the ground side of the circuit instead of the normal hot side of the circuit. ]
So, if one was to hook a wire to the ground of the chassis [ or neg. bat ]and touch it to the ground side of the blower [ blu wire going from blower to the reg], he is simply eliminating[jumping] the REG out of the circuit. Doing so also eliminates the variable speeds of the blower cuz that is what the regulators function is. So, you now have direct bat voltage to the blower .
You will see many postings here recommending one to take the blower out and hook it to a bat , direct 12v , etc.....not needed with this simple test

.. touching the blu wire to ground does this without removing anything. It is just a quick test to verify blower and diagnose Reg...
.. this is always the second test... the first test is the connector behind the booster for voltage verification from the control panel before pulling the firewall apart for nothing....
Just remember this .. the regulator is at the very end of the complete circuit, so one wants to verify voltage feed before just jumping on the reg ..

Thanks for the replies.
I take it the booster refers to the brake booster?
It's raining out right now (wishing I had a W124 shop manual...) but I will scope it out when it stops.
Thanks again, Bob

[Robert W. Roe]

Originally Posted by lee polowczuk

did you check the external fuse on the drivers side just in front of the master cylinder?

it's in its own black rectangular box.

Wow, thanks!
I checked this, and that 30A strip fuse had a hairline crack; I guess it blew.
I bridged it with a couple of alligator clips, and voila, my fan blew.
Now to get a replacement; my semi-useless local MB dealer is out of them...
Looks like your advice saved me $300+ a lot of work
Thanks again, Bob

[rjk]

Finally got around to pulling the blower motor (not hard, just fiddly and time consuming). It feels like the bearings are siezed. It is difficult to rotate the armature. I put on a few drops of WD-40 and it loosened up a small amount but by no means is it turning freely. Both brushes looked OK and moved freely in their holders. Am I correct in assuming it is off to the the pick-n-pull I go? A new one (no dust filter by the way) can be had for between $100 and $350 depending on manuf. and vendor (eBay is cheapest). Got a few quotes on used ones w/guarantees & shipping for as low as $65. Anyone know of a better idea??

[rjk]

Are blowers rebuildable by the avg. BYM? Are parts (bearings) available?

[rjk]

Just got a used blower in the mail. It, too, has what I consider to be tight bearings although not as tight as the old motor. It is not what you would call free-spinning, if you spin the wheel by hand it will stop withing 1/4 turn. Is this normal? Does it feel tight because of the permanent magnets?

Anyway, I'm installing the new unit today. Wish me luck.