No power at fan card

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oilyspanner
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No power at fan card

Post by oilyspanner »

The ventilation fan on the TZD has been intermittent all year. following toms info I modded one of the spare cards but find i have no voltage at the board apart from backlighting?
Stewart
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AndersDK
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Post by AndersDK »

That is correct Stewart !
The fan speed module is in the <font color="red"><i>earth</i></font id="red"> path of the blower motor, which means the +12V is feeded to one side of the fan (via fuse F2), and then the other side is earthed via the speed module, which in effect is an electronic variable resistor.
If you can not get the fan at work, and the speed module appears "dead", then you most sure have either a fan motor brush problem or the motor harness plug just in front of the blower is corroded.
A dead sure indicator on worn motor brushes is the fan motor suddenly springing into life when you fiddle with the cable harness in the scuttle panel.
tomsheppard
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Post by tomsheppard »

I'd add that the bus bars to the fan within the casing often become a little loose, only allowing electrons through in single file. A good strip of the fan box, cleaning everything up (Comm, fan cage and terminals; whip the brushgear apart and give it a good clean up too.) and giving the bearings a darn good soak
will almost certainly double the air throughput. Drill the casing above the motor while it is out so you can lube it once a year at the brush end. Gaffer tape over the hole when done. Anders is dead right about the module being in the earthy side but I dispute the brush problem. Nine times out of ten, it is the bus bars. If you connect a headlight bulb in place of the fan motor, then you should see it respond to the control. If it does, open the fan casing up. if not, the problem lies elsewhere.
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uhn113x
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Post by uhn113x »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">only allowing electrons through in single file. <hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
[:D]Must remember that description, Tom! [:D]
oilyspanner
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Post by oilyspanner »

Fan removed stripped and cleaned, still no action, I removed the connector from the Transistor/resistor thing, multimeter reveals 3 lives and one with no current, bridging live (thick pale blue wire and the yellow one showing no current ) gives me full speed on the fan, so is it this part of the system thats at fault or the card?
Stewart
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Post by tomsheppard »

Until somebody explains to you the relationship between voltage and current, I couldn't possibly comment.
I suspect that you have shorted across the transistor which is what the high speed relay does.
This suggests that the transistor is always biassed off or is broken. My circuit diagrams are at home so I'll look this evening and tell you tomorrow what to try next in order to establish what is wrong.
oilyspanner
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Post by oilyspanner »

Problem solved, a trip to the breakes got me a transistor, fitted that and we have a fan that works, It probably benefitted from the strip and clean/lubrication too, finished off by popping in a fan card modified as per Tom`s instructions, lovely, slow, fast and a clicking relay.
Thanks to all who contributed.
Stewart
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Post by tomsheppard »

Excellent! glad you got it fixed.
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