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#1
06-06-2006, 11:33 AM
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Blower Regulator? Anything I am missing? 87 300TD
As summer has arrived, I have decided to attack the climate control until it is spitting ice cubes.
The Car - 1987 Mercedes 300TD The Problem - Blower does not respond to the climate control switch. What I have done: Searched and read the forum. Read the 124 CDs. 1. Removed blower motor and tested on the bench. With 12v and 3 amps, motor spins but slow enough to stop with my hand. As I recall from a prior thread, the motor can draw 28 AMPs, so it seems pretty good at three amps. Should be noted that I replaced the motor about 2 years ago with a new OEM Mercedes motor. Conclusion: Motor OK 2. Swapped climate control button assemblies. I have an extra from the junkyard that I tested when the system was working. Swapped in unit did not change problem. Conclusion: climate control buttons are ok 3. Disconnected Aux Pump for heater, thinking it might be clogged or inefficient with age and stealing much desired amps. No change. Conclusion: Aux Pump ok 4. Wiggle ignition key in tumbler and found no change. Conclusion: Tumbler ok 5. Removed and checked blower fuse link in front of the fuze box. No visible cracks. Checked continuity with meter, no problems. Jumped wires to be sure and the issue was the same. Conclusion: fuse ok 6. Tested voltage at blower contacts. With fan on high, low or auto, there is 13.5v. No change when pushing blower switches. Connected contacts to blower motor and blower turns slowly. Easily stopped with hand. Measure voltage in parallel with contacts while blower connected and turning - measures .5v. Now, not completely sure I have this part right. Set meter to 10A and connect in series with positive wire to blower. Measures just a few milliamps. Hardly anything. While I had the meter out, checked continuity across motor which measured less than 1 ohm. Conclusion: Regulator bad? Things I didn't check because I forgot: Measure voltage at blower connector at firewall. I cleaned, dried and reseated the connector, but I forgot to check the voltage. I know I read what voltages I should be looking for but can't find them now. Does anybody remember what the voltages should be at that 3 pin connector? Sounds like the blower regulator to me, but before I dropped the siginificant cash I thought I would check with the experts and see if they could think of anything I forgot. Did I forget something, experts? Is my logic flawed? Many thanks in advance. Mister Jalopy. 
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#2
06-06-2006, 11:46 AM
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IIRC the PBU sends a signal between 0-5V or 0-7V to the blower controller. The blower controller sends constant +12V through one wire and a variable voltage through the other wire - close to 0V for max, close to +11V for min or something like that.
Sixto
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#3
06-07-2006, 10:08 AM
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After as much troubleshooting and problem isolation that I could think of, I pulled the trigger and bought a $75 used blower regulator from Sun Valley Mercedes. Not only did it fix the problem, but I am completely surprised by the amount air it pumps out. I have been in lots of 124s and they must have all had a weak regulator or motor.
THANKS!
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#4
06-17-2006, 06:33 AM
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Quote:
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#5
07-04-2006, 06:01 PM
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Quote:
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Linear Mode
