'97 SL500 Bower circuit problem
 

Hello everyone. I have a 1997 SL 500 with auto climate control. BAir is cold but I am losing blower activity , comes on for a minute or two then nothing. All other a/c funtions seem normal. I think I narrowed it down to the blower regulator. I solid state sealed control piece mounted to the top of the blower motor.

Where is the best place to purchase ? Part number is a Behr # W0133-1597985 list is around 500.00 clams.

Any suggestions?

Looks like about the same cost from our host (fastlane tab above).

Make certain to check the blower motor with 12v too. The brushes go out.

How did you diagnose the regulator as the fault ??

96 sl500 blower motor
 

I think I have the same problem.
1996 SL 500 BLOWER FAN. was working at low speed in ac mode but not at any advanced speed, worked at higher speed in defrost but now is not working at all for heat or air. Problem? where is blower motor located and how to remove. Thanks

I removed the blue and red wires from the motor and supplied direct 12v and ground and the motor will run contantly.

What you shoud have done is left the wires on the blower and test from Red to ground for 12v...if YES, then take a jumper wire and go from the blu wire and ground the other end of jumper..if that starts the blower high speed , then the reg is not supplying the ground [ the red at motor is ALWAYS HOT with key ON, the switching is done by the reg on the ground side of the circuit...it is a Switched Ground circuit} Blu jumper is REG By-Pass.
If no 12v at red w/key ON , you have a bad fuse link up on top. If motor runs with blu wire jumper , then the reg is bad or it has no trigger voltage from the yellow wire.

Yes, I did check current on red supply wire, B+ voltage. Also have good ground thru the blue. When reattaching bl & red there will be a small spark and then nothing. Just 12v on the ground side (blue). It must be the regulator.

If you have 12v at the red and you ground the blue side w/jumper , do you get full fan????
That is Test # 1.

Yes

Thank You

Test #2

You should have Variable voltage [ 2v-9v ] form the yellow wire to ground, dependent on which speed the Control Pnael is set at.
This is the TRIGGER voltage that trips the regulator transistor to get ground switching to complete the motor circuit ..if NO V at yellow, then the problem is upstream at the CP.. and if NO V at yellow, you can change regulators till the cows come home and the blower will still not work. if yes Variable V at yellow , THEN the regulator is bad.

Jus don't want to see you buying a reg and wind up with 2 good ones b/c you did not complete the test for Blower Control Circuit. See is all the time.

Thanks, I appreciate that. I will be checking that trigger voltage tonite. The control panel does indicate fan speed demand. I assumed it is getting the signal to the regulator. But you know what happens when you assume.
Thanks.

I hear ya..

For those reading, the basic blower control is simply a motor [ power fed by that notorious fuse link] with a regulator on the ground side that controls the speed..the switching transistor in that regulator needs a variable signal from the CP to work..That is the yellow wire.
So, a blower circuit has a simple, 3 step , sequenced test procedure.
Test #1:
Check Red @ motor for 12v..if NO, fuse link is suspect. If Yes, go to test 2
Test # 2:
Ground jumper Blu wire from motor to ground. High fan should result..if Yes, go to test 3..if NO ,blower motor is bad [ brushes/bearings ,etc]
Test #3
With CP on Defrost and Key ON, check yellow wire for Variable V , 2-9v --if Yes, reg is bad, If NO, CP is suspect.

What Benz was nice enough to do was there is a 3 prong plug up top
on most models that have the 3 feed wires [ R/Blk/Yl] , so you do not even have to go to the motor/reg to do the diagnostic power test...they can be tested right at that plug. [ Red/12+..Blk 12 -..Yl/ Var V.+ ]
A Tech would never go down into the blower compartment until he took readings at the top side plug.
It's all in the Archieves,,,,,,,,,,,,,,,,,