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heater control stays on-key off??

imfixinmopars on Wed December 19, 2007 5:27 PM User is offline

Year: 93
Make: olds
Model: 98
Engine Size: 3.8
Refrigerant Type: n/a
Country of Origin: United States

we are having a problem w/ a loaded 98. the heating system semi-stays on when the key is shut off. the battery is drawn down overnite.any ideas? i know this is more tuned to a/c questions,but i need help. it has dual zone heat,and digital temp control. thanks,mike

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working on old junk to afford to fix my old junk,lol

Chick on Wed December 19, 2007 5:41 PM User is offlineView users profile

Are you saying the blower motor stays running? If so, you need to change the blower motor modual, which takes the place of the blower motor resistor..You must have ATC right? If that is not the problem (blower motor running) then try to give us more info..I can post a pic of the modual if needed..Hope this helps.

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

imfixinmopars on Wed December 19, 2007 5:46 PM User is offline

i believe the motor keeps running.i dont have the car here in the shop just yet.the batt was disconnected and it seemed to stop the motor from running? maybe it kept running later? drawed the batt flat over nite,sorry for the lack of info at this time.

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working on old junk to afford to fix my old junk,lol

Chick on Wed December 19, 2007 5:54 PM User is offlineView users profile

If the blower kept running, it's the modual, very common on GM ATC systems. Usually get a few every summer. Here's a pic of the one for ATC..Hope this helps..



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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

Edited: Wed December 19, 2007 at 7:53 PM by Chick

Chick on Wed December 19, 2007 6:03 PM User is offlineView users profile

In case you can't locate it, you remove the beautification cover over the blower motor and relays, and two 7mm screws hold it in the heater box under the hood on the firewall..Hope this helps..





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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

Edited: Wed December 19, 2007 at 7:49 PM by Chick

Cussboy on Wed December 19, 2007 7:09 PM User is offline

Quote
Originally posted by: Chick
In case you can't locate it, you remove the beutification cover over the blower motor and relays, and two 7mm screws hold it in the heater box under the hood on the firewall..Hope this helps..





Chick - don't you mean "module" ? and "beautification"

Chick on Wed December 19, 2007 7:39 PM User is offlineView users profile

Hey give me a break, two years ago I couldn't spel Graduate, now I are one....

But yeah, thats what I meant....

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

Edited: Wed December 19, 2007 at 7:44 PM by Chick

NickD on Wed December 19, 2007 9:04 PM User is offline

The module in my 92 DeVille is much smaller using a thick film mounted power MOSFET transistor, see on the one you pictured, using a good old fashion TO-3 case transistor, these have been around since the early 60's. Must be some control circuitry underneath, it would be interesting with a new unit to remove that T0-3 and put it in a curve tracer to get the characteristics of the device as more than likely the one in this Olds is shorted out, can't tell much from that. Maybe a replacement can be found for a couple of bucks.

Most of these circuits are protected by a 30 amp fuse, but seems with higher than normal blower current, that transistor shorts out first before the fuse blows presenting the question, what in the hell is the fuse in there for? Maximum blower current on most GM ATC vehicles is 22 amperes, can be a lot higher for a couple of reasons. First is that the tiny oil wick runs dry, steel shaft rusts solid to the bronze bearing causing the bearing to spin in the sheet metal housing causing excessive drag on the motor. It will still run, but the current can be very close to the fuse rating that will burn up the module. Second reason is that the blower wheel chops up debris that is sucked into the blower via the brush cooling tube packing around the armature causing severe drag. Either case, can't either clean nor lubricate the motor, it has got to be replaced.

So just slapping in a new module with a dragging motor will pop the new module costing more than a couple of bucks, just on general principles, also good to replace the motor as well.

In some real disastrous cases, a blown transistor also blows the control circuit that shorts out the BCM really adding to the expense of the repair bill. But that is more rare.

(edited to correct the spelling on modual)

Edited: Wed December 19, 2007 at 9:05 PM by NickD

Chick on Wed December 19, 2007 9:12 PM User is offlineView users profile

More like the one pictured here Nick? Bad pic, but most are like that. I use the other one cause it came out a little better...



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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

NickD on Thu December 20, 2007 7:21 AM User is offline

There are really cheap ways to protect these things, cheapest is an on chip thermistor to shut down the pass transistor if the chip gets to hot, but it is too slow for transient type currents, the better is to use a piece of metalization as a current shunt and the collector or drain voltage fed into a multiplier that limits the power dissipation of the pass transistor to safe levels, adds about 3/4 of a cent to the cost of the chip. They wouldn't here of this, so instead the user gets a popcorn seed in a frying pan with red hot oil just waiting to pop for a tidy price tag of from 100-200 bucks.

Don't blame engineers, either you do what you are told, or they will find someone else, and there is someone else.

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