Weird electronics issues - heater turns on for no reason

Discussion in 'Freightliner Forum' started by fooomanchu, Aug 4, 2013.

  1. fooomanchu

    fooomanchu Light Load Member

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    Oct 19, 2012
    Urbana IL
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    2009 Cascadia with Detroit 60 - 600K miles. Sometimes when the truck is parked and the key is not even in the ignition (especially in wet weather) the heater/ac blower just comes on and stays on. This is not a serious problem for me because I can just shut off the master power switch on the truck, and I still have the bunk heater and air conditioning. Mechanics tell me it's corrosion in the "brain box." My concern is that other bad things might start to happen, eg. the truck might shut off when I'm going down the road, or someday the truck won't start (or maybe I'll accidentally fire a missile at Cuba...you get the idea). Within the brain box, is the heater stuff anywhere near stuff for more important things? Should I assume that if I'm having problems with just the heater other problems are likely?


    I've been told you can't clean corrosion off the brain box - you need to replace it, and it ain't cheap.
     
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  3. NYROADIE

    NYROADIE Heavy Load Member

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    Jun 24, 2010
    Rochester NY
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    I assume that you mean the ECM and if thats the case I really don't see how the ECM would turn on the blower motor. But remember i said assume! I think it's much more likly that somewhere/somehow you are getting rain water into or on to the fuse panel and that it causeing a live short and energizes the blower motor. Have you ever tried just turning the blower switch itself off? That could give you a direction to go from. Don't just throw parts at it, you'll just end up wasteing money. Has the windshield ever been replaced? If it has start looking for leaks there.
     
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  4. fooomanchu

    fooomanchu Light Load Member

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    Oct 19, 2012
    Urbana IL
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    Haha I really have no idea what I mean. A couple mechanics referred to it as the computer box and the brain box.





    The manuals I have are totally useless. From what I understand there are...two fuse boxes? I had my entire windshield and all the rubber replaced last year and this seemed to solve all the leaking issues I had. I'm pretty sure the fuses under the glove compartment are okay. I don't think it rained last night but the air was really wet.



    No. I'm not even sure where this is. I'm mostly worried about bigger problems, though. From what I gather from what you said, it sounds like my problem isn't necessarily an indication of worse and bigger things to come, so I'm not worried so much. Seems to be okay when the sun comes out...


    Thanks for all the help!
     
  5. baha

    baha Road Train Member

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    Jul 25, 2013
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    mine did that 4 a bit then quit turning off with key ck n clean con at firewall both sides
     
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  6. Chip S

    Chip S Light Load Member

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    May 27, 2013
    Texas
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    Sounds like it is time to replace your SAM cab. We have had a few of them catch on fire, due to corrosion. Google the FL545 recall for your 2009 cascadia
     
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  7. fooomanchu

    fooomanchu Light Load Member

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    Oct 19, 2012
    Urbana IL
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    I appreciate the help....Could u give a little more info about what this is exactly, or where it is, and how to clean it? thanks
     
    Last edited: Aug 6, 2013
  8. fooomanchu

    fooomanchu Light Load Member

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    Oct 19, 2012
    Urbana IL
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    Will do - thanks for the advice

    edit - sam cab on my truck was already replaced (recall). If this is what the problem is, they said i need to pay for it this time around! These things must be made cheaply and not last long.
     
    Last edited: Aug 6, 2013
  9. Chip S

    Chip S Light Load Member

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    May 27, 2013
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    We have not had too many issues with them, except when a windshield leaks.. They dont take water too well. You can see the corrosion if you remove the glovebox, sam cab cover and pull each connector one by one. The blower motor is a 4 pin connector with 2 blue and 2 black wires coming out of it. The front a/c controller is in connector X1 if I remember correctly. X1 is the front left connector out of the sam cab.. right next to the windshield.. Unfortunatley there are all time voltage from other circuits as well as the ign circuit for the front controller, so voltage backfeeds through the connector all time.

    Good luck
     
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  10. fooomanchu

    fooomanchu Light Load Member

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    Oct 19, 2012
    Urbana IL
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    I'll give it a shot - thanks for all the help!
     
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