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  #1  
Old 04-09-2008, 03:18 PM
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Question Failed A/C-Heater Blower.

My heater blower has ceased to operate and I am searching for causes. I removed and checked the dash push button heater control unit and the blower switch part seems to function okay? Next I removed the blower regulator module (behind glove box) but cannot tell whether it is at fault. They are expensive, so I want to make sure whether it is working or not... can it be tested somehow?
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Old 04-09-2008, 10:46 PM
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You need to get a wiring diagram (on the CD or from alldatadiy.com). IIRC, the blower control module switches ground WRONG - IT SWITCHES POSITIVE - SEE LATER POST !! between the various contacts on the resistor pack to give the desired blower speed.
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Last edited by ctaylor738; 04-10-2008 at 03:24 PM.
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Old 04-09-2008, 11:49 PM
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Bizzare, but true:

It could be the ignition switch (the electrical part). On my 560, it was very intermittent but I found that I could briefly get it to work by jiggling the key. Replacing it is unpleasant but the part's only $25.
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Old 04-10-2008, 01:26 PM
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Quote:
Originally Posted by ctaylor738 View Post
You need to get a wiring diagram (on the CD or from alldatadiy.com). IIRC, the blower control module switches ground between the various contacts on the resistor pack to give the desired blower speed. So the test is, with the module removed, to find the pin for one of the speeds, and supply the ground. If the blower comes on, the module is the problem. Otherwise, you need to keep looking.
Thanks for your response..........I assume you mean find a pin hole in the module receptacle and supply a ground to? .....right?
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Old 04-10-2008, 01:39 PM
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Quote:
Originally Posted by Strife View Post
Bizzare, but true:

It could be the ignition switch (the electrical part). On my 560, it was very intermittent but I found that I could briefly get it to work by jiggling the key. Replacing it is unpleasant but the part's only $25.
Thanks Strife.........it does sound rather odd, but worth checking out....will let you know if it works. While i have your attention Strife, do you know what is behind and also how to re and re the carpeted hump below the steering wheel, in front of the drivers knees? Mine needs a bit of fixing, as it has become loose on the right side.
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Old 04-10-2008, 03:22 PM
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Oops!

I just looked at the diagram, and I was wrong. The control module switches positive, not ground. So forget what I said.

You need to check for 12V input at Pin 12 from Fuse #8. Then power goes out through Pins 3, 4, 6, 7, 8 and 11 to the resistor pack, where it gets stepped down or up to vary the blower speed, then to the blower. If the relay decides on low power, that would go out Pin 11, and full power is Pin 8. It looks like the input from the push-button unit is on Pins 2 and 9, and 10 is ground.

I need to think about how you would test this, since the problem could be in either the push-button unit (not sending a signal), or the fan relay (not sending power out).

You did check Fuses 7 and 8?
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Old 04-10-2008, 04:00 PM
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knee bolster

That carpeted thing beneath the steering wheel is a bolster that is supposed to prevent "submarining" of the driver in a frontal collision. It is attached by two keyholed bolt arrangements. The keyhole slots are in the bolster and they mate with two bolts that protrude from under the dash.

Try moving the loose side around slightly while applying light upward pressure until you feel the bolt head drop into the large end of the keyhole. Then a firm push straight back should seat it. If this doesn't work, it is possible that one of the bolts has fully unscrewed and has dropped out.

In that case, pull the fastened end outward and drop the bolster from the remaining keyhole bolt. Remove the whole thing and look under there. You will see how the arrangement works and should be able to easily repair it.

Let us know how you make out.
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Old 04-11-2008, 02:08 PM
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[QUOTE=ctaylor738;1820379]I just looked at the diagram, and I was wrong. The control module switches positive, not ground. So forget what I said.

You need to check for 12V input at Pin 12 from Fuse #8. Then power goes out through Pins 3, 4, 6, 7, 8 and 11 to the resistor pack, where it gets stepped down or up to vary the blower speed, then to the blower. If the relay decides on low power, that would go out Pin 11, and full power is Pin 8. It looks like the input from the push-button unit is on Pins 2 and 9, and 10 is ground.

I need to think about how you would test this, since the problem could be in either the push-button unit (not sending a signal), or the fan relay (not sending power out).

You did check Fuses 7 and 8?[/QUOTE]
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Old 04-11-2008, 02:13 PM
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Hi cTaylor,
Thanks for response including the research you are doing to help out on this problem.
Yes, I did check fuses 7 and 8 and they appear to be okay.
Will await your next suggestion......very much appreciated, thank you.
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Old 04-11-2008, 02:15 PM
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Re Knee bolster.

Let us know how you make out.[/QUOTE]
Will do Rocky Raccoon, thank you for sharing your knowledge.
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