2004 Toyota Sienna rear fan

2004 TOYOTA SIENNA
90,000 MILES
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WOODY98223
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The rear HVAC blower is inoperative. A mechanic troubleshot and determined that the rear components were all good, but no power supply to rear HVAC blower relay from HVAC control head in front dash. Recommended replacement of 8401008010 control head. I purchased a used control head (sold as checked & guaranteed), did the easy replacement in dash (identical part), but same problem, so I returned the part. Any ideas? $20 reward for right answer!
Aug 1, 2013 at 2:51 PM
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KHLOW2008
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Chart shows possible causes.
Are you able to perform electrical testings and do you have a DVOM available?
Are there any trouble codes?
Is HVAC system automatic or manual?
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Aug 2, 2013 at 8:15 AM
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WOODY98223
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Thanks, The general service shop that did the troubleshooting had the dash open and rear AC access panel removed and determined that there was no power supply from the control unit in the dash - It's a basic LE with manual controls. The front blower & AC works fine, but no rear blower - but he said switches are OK. Used electrical components are never recommended, but it seems unlikely to me that both control units have sane defect. Is this a 'plug & play' control head or does it need to be programmed in? Thanks!
Aug 2, 2013 at 10:19 AM
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KHLOW2008
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Electrical circuits for non working components are diagnosis straightforward. Power suply must go in somewhere and make a complete circuit for the components to work.

Used part or not does not matter. Even new replacement parts are known to fail.

You need to test and find out where the power suply is disrupted.

Component is plug and play.
Aug 3, 2013 at 11:18 PM