Variable resister most common cause of failure.
For an inoperative blower motor, not a charging system failure.
Switching on lights and accessories increases the load on the charging system and can expose a weakness. Everything is fused, there should be a 20 or 25 amp fuse on the blower motor circuit to protect the wiring so it isn’t possible for the blower motor to draw 90 amps exceeding the capacity of the alternator.
@Nevada_545 - so what are u saying?
As it is, the alternator only fails when the cooling fan is set to high - no other times alternator fails.
Why should the “cooling fan is set to high alone” be the bigger load than all other combinations?
The people who re-manufactured the alternator are known well.
Thinking in terms of the construction of a basic variable “resistor”, setting it to high speed is like having the pair of wires from the blower fan connected across the 12 VDC. If the motor is shorting, then this could happen? Or it could be anything.
If the blower motor is working then the power input line to it cannot be shorted, besides it should blow a fuse if it was shorted. The motor also draws the highest current when it is set to high, power running directly to the motor instead of having inline resistors with the power in order to lower the motor speed.
You say that the charging fails somehow when the blower is set to the HIGH position. Tell us exactly what you mean by saying “fails”. Even though it is possible the blower is drawing excessive current on the HIGH position, the charging system should be able to keep up with the current demand. You don’t state what other loads you have going at the same but even if the head lights and cooling fans were on at the same time there shouldn’t be a problem. Another question I have is, does this problem change when the engine RPMs are around 1,500 RPM? It would also be good to have the current draw of the blower checked to see if it is drawing excessive current. Make sure nothing is restricting the fan movement as that will increase the current draw. You can check the current draw at the fuse but you will need a meter that can handle at least 10 amps of current. I would say that normal current draw should be less than 8 amps on the high position if things are okay.
Tested at idle speed - Parts shop connected their device across the batt terminals to check Alternator:
Next time, I will have the RPM increased to 1,500 RPM to check it again.
Can’t the variable resistor could short at the HIGH speed terminal too right - or some loose connection? The excess current may not be enough to blow the fuse but to overload the alternator? Or the fuse may not be working properly?
RPM should not have an effect whether lights or HACV fan is on low or high. You are making this to complicated and you need to find a competent shop.
Actually RPM had an effect - with idle rpm, alternator was found to be producing low voltage compared to cold start rpm.
Alternators can’t produce their rated output power at engine idle speed. A better test is to check the voltage while the engine is running around 1,500 RPM.
You need to check the voltage at the output of the alternator. Also check the voltage difference between the output stud and the positive battery post.
When the fan is on the high setting there is a direct connection to power, nothing is in line to the motor. If a short in the power somehow happens then a fuse should blow out. Get the current draw of the blower motor checked out to see if there is a problem with it.
Continuing on @Cougar 's theme, is the engine idling at the proper speed
So I tested again - Parts shop connected their device across the batt terminals to check Alternator.
At idle speed: Idle on this car is around 750 and it idles correctly
At idle with fan at HIGH, the voltage was jumping between 12 and 14V.
Tested at just under 1500 rpm
Any similar experience? What seems to be happening?
Why not return to the shop that rebuilt the alternator for a professional diagnosis? There must be some warranty on the rebuild.
Yes there is warranty - I will be returning
The parts shop thought that it is the diode.
I did go back to the repair shop and there was no issue
So I went to a competing parts store and they confirmed all is good - so I returned to same brand part store in a different location and alternator passed too. Eventually went back to the same parts store but their machine had battery issue. Oh well I decided to give up on keep testing.
I do know that this car has some self healing properties - for sure it has happened before. Perhaps after all the changes the car might have took some time to adjust to the new electronic chips.