Hi again,

I finally manage to pull the AC Control Unit off. Attached are the pics I have taken. Surprisingly with the AC Control Unit disconnected, the Blower still kept blasting away. Is it back to the Regulator or even the Thermo Sensor Switch Faulty?

Can some one pls lead me in the right direction very much appreciated.

Attached Thumbnails

     

Wondering why removing Fuse no 4 & 7 The Blower kept blowing?

I will put the switch or control unit back in the front dash. However I notice there 2 white plastic (pencil like) which need to be inserted into the 2 plastic behind the dash. What procedure do I look for, in putting the swicth back?

Hi,

I finally put the AC Control Unit back in the dash. I have tested the 3 pin wires using a Multimeter.

(1) Test the middle pin with AC switch disconnected--->0 Volts & plugging the 3 pin wire to the Blower turn ON full blast
(2) Test the middle pin with AC Switch connected ----->12 Volts & plugging the 3 pin wire to the Blower turn ON full blast
(3) Test the middle pin with AC switch connected (a) Switch 1---> 11 Volts (b) Switch 2--->10 Volts (c) Switch 3--->9 Volts (d) Switch 4--->8 Volts (e) Switch 5--->5.5 Volts
(4) With Engine On, test the middle pin with AC switch connected (a) Switch 1---> 12.5 Volts (b) Switch 2--->12 Volts (c) Switch 3--->11 Volts (d) Switch 4--->10 Volts (e) Switch 5--->7 Volts

Whats odd is that the Blower keep blasting away with or without the AC Switch connected or disconnected.

But the Multimeter detected 12 Volts in the middle pin when the AC Swicth is connected but 0 Volts when discoonected?

This motor is controlled by a three legged relay made out of silicon, it is doped with some chemicals and then labled "blower motor regulator" AKA: Power Transistor

ok, so the relays are in fact now the Regulator.

From the result of my test using a multimeter are you suggesting its the Blower Regulator, the most likely culpril?

Like MB DOC said way back when, the blower regulator is it's own solid state
control unit that can fail. It will run away on it's own when it fails.
It is powered directly via a 16mm circut 30 power wire with a 200 amp crash fuse. The distribution block (X4) that it connects to is under the driver's carpet below the gas pedal on a left hand drive car.
If you want to stop it from running, unplug the regulator at the blower fan.
Disconnecting it upstream will kill your igntion switch and traction control
power supplies as well.
The stepped voltage from the head unit it the control voltage for the
regualtor to dictate needed fan speed.
Your voltages are right in spec. You 99% need a new blower regulator
unit.
Regards,
DR.D

__________________
Dr.Diesel -
Shop Foreman
Master Guild Mercedes-Benz Technician.

Think the dealer is expensive? Do you know how much it costs to train a dealer tech? Or buy the required MB special tools to have on hand?

DR.DIESEL,

Thank you very much. I'm glad the diagnoses is pointing to Regulator rather than the AC Control Unit. But before concluding, out of curiousity, can I ask a few more questions:-

(1) When testing the middle pin, why is the voltage increasing as the switch reduce from 5 to 0. Some 1 suggest as the swicth increases, so should the voltage?

(2) Can you recommend a www site to purchase at a reasonable price?

Kind regards

http://catalog.peachparts.com/

Note:
I edited your title to include "dash blower".

Whunter,

Yes to which question please?

your problem is the regulator, most time they get wet, due to rain water or run car through car wash,take it out and dry it well, but you need to check for water leak inside the car, is the floor matt wet passenger side?

-------------------------------------------------
Quote:
Originally Posted by rmt6668
Can you recommend a www site to purchase at a reasonable price?

Yes...

http://catalog.peachparts.com/

Please help ! Somebody out there !
Mercedes Benz 380 SE 1984 model, Automatic Transmission
Problem : in cooling mode heat is being blown from the dash board and cool air is coming from cooling vents. I replaced a new Mono Valve and removed CCU opened it , found no visible problem with CCU and reinstalled it . The problem remains the same.

380 SE , 84 how to reach blowe fan in the dah