Possessed!! Part Deux

littleredrooster · Post by **littleredrooster** » 19 Aug 2005, 13:58

Driving to work this morning, the bloomin' thing frightened me to death when, for no apparent reason, the ventilation fan suddenly went to high speed. Now I know it does this when there is a big temperature differential going on, but that wasn't the case this morning. Moreover, the fan now will not respond to the manual slider control. All positions on the control (including 'Auto') leave the fan on high. Air-con was not on, temp slider was set to cold. I have tried various combinations of the heat slider, air recirculate and direction controls without success. Air con on or off makes no difference either.
Any ideas???
Car is a 2001 Xantia HDi, BTW.

lurchy666 · Post by **lurchy666** » 19 Aug 2005, 20:04

it could be the resistor pack which does the speeds on the fan

samtronic · Post by **samtronic** » 19 Aug 2005, 20:08

It sounds a lot like this thread:
http://www.andyspares.com/discussionfor ... C_ID=14941
Søren

uhn113x · Post by **uhn113x** » 19 Aug 2005, 22:02

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by littleredrooster

Driving to work this morning, the bloomin' thing frightened me to death when, for no apparent reason, the ventilation fan suddenly went to high speed. Now I know it does this when there is a big temperature differential going on, but that wasn't the case this morning. Moreover, the fan now will not respond to the manual slider control. All positions on the control (including 'Auto') leave the fan on high. Air-con was not on, temp slider was set to cold. I have tried various combinations of the heat slider, air recirculate and direction controls without success. Air con on or off makes no difference either.
Any ideas???
Car is a 2001 Xantia HDi, BTW.
<hr height="1" noshade id="quote"></blockquote id="quote">
There is probably a transistor in it to switch speeds, and it has probably gone short-circuit.
HTH

Post by **Peter.N.** » 20 Aug 2005, 03:54

If its the same blower that the XM uses it has two transistors mounted on the motor assembly that go short circuit. The easiest thing to do is get a secondhand motor, but you can replace the transistors if you feel inclined, they are TO3 type, PNP, 15 amps +, they are riveted in so you will have to drill them out and replace with nuts and bolts.

uhn113x · Post by **uhn113x** » 20 Aug 2005, 13:10

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Peter.N.

If its the same blower that the XM uses it has two transistors mounted on the motor assembly that go short circuit. The easiest thing to do is get a secondhand motor, but you can replace the transistors if you feel inclined, they are TO3 type, PNP, 15 amps +, they are riveted in so you will have to drill them out and replace with nuts and bolts.
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Trust them to use PNP! Maybe 2N2955 OK?

Post by **Peter.N.** » 20 Aug 2005, 13:47

Dunno what the rating of that one is, but if its 15a or more, should be OK. Yes, there are plenty of NPNs! I thought they made a PNP version of the 2N3055 but I cant find it, unless thats it.

Mandrake · Post by **Mandrake** » 20 Aug 2005, 14:30

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Peter.N.

Dunno what the rating of that one is, but if its 15a or more, should be OK. Yes, there are plenty of NPNs! I thought they made a PNP version of the 2N3055 but I cant find it, unless thats it.
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The 2N2955 is indeed the PNP complement of the 2N3055, however I'd recommend something a bit more beefy as having built a number of linear regulators over the years (using similar transistors) I'm not that impressed by the 2N3055. (And it's complement the 2N2955)
They're a very middle of the road transistor, a bit prone to failure despite staying within their theoretical ratings, and the usual reason for failure of power transistors is simply not having enough safety margin in the ratings of the device. (EG cost cutting)
For the sake of a few dollars its better to get something with a bit more safety margin, especially if the original type was a bit underspeced for the job, which sounds like the case, based on the number of people that have this problem occur.
There is simply no alternative to rugged ratings and overspecing if you want reliability in the realm of power transistors.
For PNP I'd recommend a transistor I've used a lot, the Motorola MJ4502: (It's NPN complement is the MJ802 in case anyone wants to know)
http://pdf.alldatasheet.co.kr/datasheet ... J4502.html
90 volts, 30 amps, 200W, hfe 25-100, compare that to the 2N2955:
http://pdf.alldatasheet.co.kr/datasheet ... N2955.html
60 volts, 15 amps, 115W, hfe 20-70.
The MJ4502 is a very rugged transistor and superior in every regard, is a dropin replacement, and isn't that much more expensive considering the annoyance of possibly having to replace the cheaper one again, should it too fail in the future...
Regards,
Simon

littleredrooster · Post by **littleredrooster** » 26 Aug 2005, 14:56

Mysteriouser and mysteriouser!! After five days of having a full-blast fan going, it has suddenly resumed normal operation. Responds to slider exactly like wot it should. What is going on????

Mandrake · Post by **Mandrake** » 26 Aug 2005, 15:27

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by littleredrooster

Mysteriouser and mysteriouser!! After five days of having a full-blast fan going, it has suddenly resumed normal operation. Responds to slider exactly like wot it should. What is going on????
<hr height="1" noshade id="quote"></blockquote id="quote">
One thing is for sure - faulty transistors don't repair themselves [:D]
Which means its something else, perhaps worn contacts on the ignition switch causing a voltage drop to the fan supply voltage as others have suggested.
Regards,
Simon