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Old 07-25-2002, 09:04 AM
Don Hicks
Posts: n/a
Blower Not Working

Car: 1989 300E

Blower not working at all.

I know the blower is good because I have had it out of the car and applied 12 volts to it. I have the blower regulator (Transistor) out of the car. Is there a way to check the blower regulator while it is out of the car. If there is know good way to check the blower regulator out of the car, how can the blower regulator be checked in the car? What are some of the other things that might cause the blower not to work properly?


Don H
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Old 07-25-2002, 09:19 AM
Registered User
Join Date: Dec 2001
Posts: 571
Look inside fuse box. Fuse number 5. If it's does not appear to be blown either reseat it or simply replace it anyway.

I've had one blow and had it's replacement fuse get unseated somehow.

When fuse 5 goes, so does your blower.
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Old 07-25-2002, 11:07 AM
Join Date: May 2002
Location: Columbus, OH
Posts: 44

There is strip fuse for the blower mounted in a black rectangular box above the driver's side wheel well.

Also check the control voltages. The connector is behind the power steering, under the front window gutter. The yellow wire is the control which should be 1v when blower switch on low, 12v when on high, and in between when on auto.

If all that is OK, short the blue wire on the regulator to ground. The blower should run at high speed while shorted.

My blower only ran on low. The regulators tend to burn out after 120K or so. My blower motor needed a little lubrication, but the problem was the regulator. They list at $300, Fastlane has them at $251, and you can find them used for $100-$125. Good luck.
Jim Wiggin
Columbus, OH
1989 300E
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Old 07-25-2002, 02:20 PM
Registered User
Join Date: Jan 2000
Location: New Bedford, MA USA
Posts: 1,583
The blower speed regulator modulates the blower speed by increasing or decreasing the resistance in the ground leg of the blower circuit. I.e., at low speed the ground leg is floating above zero, so the motor is only seeing a percentage of full system voltage (the red wire is always at system voltage). I believe it's a simple NPN power transistor in a emitter follower circuit. Anyway, to test it regulator in the car, set fan speed to high. The red lead should show twelve volts, and if the regulator is working the blue can be checked with a test light between the lead and the positive terminal on the battery. If the light activates, the the high speed is OK. Select low speed, check again, if light is dim or lot lit, then low speed is probably OK. If you get no light on high speed, then the regulator is not conducting to ground. BTW, the yellow control voltage should not get above 8.5 volts DC.
Jeff Lawrence
1989 300e
2000 Dodge Grand Caravan SE
No matter what you fix, there will always be something else to fix..
"Warranty" is just another way of postponing the inevitable.
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