Fox T-Bird/Cougar Forums  

Diagnosing/troubleshooting electric tips/tricks?

August 29, 2012, 04:31:55 PM

So, I've had this 2003 Olds Alero for way too long. I've replaced the engine in it as well as the transmission. I've also done Hubs and brakes several times over, front end linkage and shocks all around. The car is still in decent enough shape to keep around and with a "new" engine with 46K miles and a "new" trans with 6K miles on it, I feel it's worth keeping around for another year or two. I don't mind the car when it's not taunting me with issues but down right hate it otherwise, if not for spite of being a GM.

All that being said, I'm not bad with mechanical stuff but the electric/electronic side of things is not my strong suite. I'm having 4 issues with this car that have me wondering exactly what to do and how to go about dealing with them.

First and probably the most important issue. The climate control. It only works on high speed. Some inter-webs searching yielded results pointing at a resister of some sort, up in the dash/fan motor housing. I can replace parts but this seems odd to me. Is it like an in line fuse or something? And where the heck is it?

Next is the rear defrost. Not sure exactly when it stopped working (my wife drives this car most of the time). It just doesn't work. IIRC the switch lights up, but no bueno.

Not sure if it's somehow related to the rear defrost but the rear speakers stopped working. Both of them I believe at the same time.

Finally, the 12v sources are dead.

Only thing I can really say is note worthy is that I've checked all of the fuses within the car, unless they are hiding some. None of them are blown, all are intact.

Any way, I know some of you are rather talented with this sort of thing and likely have much more experience than I. Any help would be greatly appreciated. Winter's already sneaking up.

Quote Selected

Diagnosing/troubleshooting electric tips/tricks?

Reply #1 – August 29, 2012, 10:18:35 PM

Tom Renko might know off the top of his head about the resistor packs in that model, but generally speaking, blower speeds are limited by tapping off voltages in a "resistor pack", which is nothing more than several resistors in series with taped output between each resistor. Here is a quick and dirty for you:

Resistors: A, B, C and D all of the same value and wattage, for simplicity, and 12 volts for source voltage.

[GROUND]->A->B->C->D->[Source Voltage]

If I checked the voltage at the junction between B and C, I would see 6 volts (v).
If I checked the voltage at the junction between C and D, I would see 9 volts (v).
If I checked the voltage at the junction between A and B, I would see 3 volts (v).

If I use this voltage to supply the blower motor (fan), the motor would turn slower at a lower voltage, hence the speed control.  Most modern automobile bypass the resistor pack on high to avoid the high current draw through the switch.

As for the defroster and speakers, If this model has a trunk and the speakers are mounted in the package tray, you might want to check for cabling and connectors that may have gotten torn loose, usually happening when someone overstuffs the trunk and the wiring gets snagged.

Of course the two symptoms might be completely unrelated, but if no loose wiring is located, the next step would be to check for voltage (a simple test light will do) at the connection(s) on both sides of the defroster "grid" with the defroster switch turned "on", one side is going to be voltage and the other side ground. This will tell you whether or not you are getting voltage or not, but if you do, then you know that you don't have a popped fuse and that the switch is working as well.  If no voltage is present, you might have to consult the "EVTM" for that model to troubleshoot further.

By 12 volt sources, I assume you mean the jacks that look like cigarette lighter sockets, right?  If so, the outside metal part is ground and the "pin" at the back of the socket should be 12 volts or so.  Some of these are hot only when the key is on and others are always hot.  In either case, both are fused and may or may not share a fuse in the fuse block.

I hope that helps.

~C88

Quote Selected

Diagnosing/troubleshooting electric tips/tricks?

Reply #2 – August 29, 2012, 10:48:14 PM

Did you check ALL the fuses? The dash fuse box AND the underhood fuse box?  Newer cars usually have the powerpoint fuses underhood, at least more and more these days.  The resistor will be shaped like a card with a rectangular  you'll either find it by looking under the dash near the blower or behind the glove box near the blower, always near the blower as its cooled by air from the blower's discharge path.  If you Google it, you'll find a pic of what to look for.  The resistor is almost the only thing that causes this problem, rarely, the switch may do the same, buy the resistor is almost a consumable part.  Get one, you'll figure it out.  Crazy88 is right about trunk connectors, you'll almost always find one pulled apart.

Quote Selected