How long do FSR last?

[AV8R4AA]

I just replaced mine.
Looked like it was dated 34th month of 2011.
Since the X5 was built in 2003, I'm guessing it had been
replaced at least once.

Anyone care to comment on the lifespan of these hedgehogs?

[crystalworks]

I think it's hit or miss. OEM ones last a lot longer than aftermarket by rule... but they can still fail at pretty random ages/mileages.

[Zulu95]

My factory FSR failed somewhere around 40K miles.

[motordavid]

My 2001 oe factory FSR failed at ~ 50,000 miles/ early 2006.
I had the 'then version' of 'extended maintenance', and the dlr R&R'd that original.

Now, I have 113,000 miles, and that replacement still works, knock on fookin wood.
I cringe just admitting that that replacement was so long ago.
GL, mD

[StephenVA]

I still have the OE one running fine. Watch now it will fail.....

[AV8R4AA]

As for the symptoms, mine seemed to vary in output air flow.
What used to be plenty, was now a whisper.
The digital fan speed indicator didn't jibe with the output flow.

Is that an indication of failing FSR?

New FSR will part your hair now!
Well, when I had hair, that is.

[upallnight]

If you run the blower at a low speed I think you will use the FSR more since more of that energy is converted to heat, whereas if you run the blower at a high speed less of the current is converted to heat by the FSR, but since the blower motor is spinning at a faster speed, the blower motor will expire quicker.

You choose what you want to replace. Blower motor of FSR. If I don't need to run the blower motor I just keep it off.

[srmmmm]

Original lasted 78,000 miles, second OEM went 81,000 miles, third OEM has lasted 166,000 miles. On the third, the dealer did tell me BMW had "beefed it up" because they were replacing too many under warranty. Living in Texas, the blower motor is used 363.76 days per year - maybe more

2002 X5 3.0 324,950 miles (almost another milestone)
2014 428i 28,100 miles

2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles (also had FSR replaced under warranty!)

1970 Firebird - Under restoration

[oldskewel]

Originally Posted by upallnight

If you run the blower at a low speed I think you will use the FSR more since more of that energy is converted to heat, whereas if you run the blower at a high speed less of the current is converted to heat by the FSR, but since the blower motor is spinning at a faster speed, the blower motor will expire quicker.

You choose what you want to replace. Blower motor of FSR. If I don't need to run the blower motor I just keep it off.

Neither the FSR nor the blower motor are pure resistors, but they can be considered close enough for this analysis. Maximum heat dissipation in the FSR will actually occur when the voltage drop across the blower equals that across the resistor.

So when the blower is set for low power, the FSR is set to a high effective resistance and the current is low - so the blower spins slow and the FSR does not dissipate much power due to low current.

When the blower is set for high power, the FSR acts as if it has low resistance, so the current is high - the blower spins fast and the FSR does not dissipate much power due to low resistance.

A little circuit analysis and basic calculus shows the max power dissipation when the FSR resistance is in the middle. If they were pure resistances in series, it would be when R_FSR = R_blower, which would also be when V_FSR = V_blower.

So no need to worry about your fan idling at low speed. Or at full speed.

Here's a theory about why some FSRs fail quickly while others last a long time ... a weak/failing blower motor will stress the FSR. If the blower motor spins slower than it should due to mechanical problems or increased internal resistance, then the back EMF will be smaller than it should be. So the current will be higher than it should be. So the FSR will have more energy to dissipate.

So if you keep blowing FSRs, there could be a problem with the blower, either electrical or mechanical.

[wpoll]

Originally Posted by oldskewel

Neither the FSR nor the blower motor are pure resistors, but they can be considered close enough for this analysis. Maximum heat dissipation in the FSR will actually occur when the voltage drop across the blower equals that across the resistor.

So when the blower is set for low power, the FSR is set to a high effective resistance and the current is low - so the blower spins slow and the FSR does not dissipate much power due to low current.

When the blower is set for high power, the FSR acts as if it has low resistance, so the current is high - the blower spins fast and the FSR does not dissipate much power due to low resistance.

A little circuit analysis and basic calculus shows the max power dissipation when the FSR resistance is in the middle. If they were pure resistances in series, it would be when R_FSR = R_blower, which would also be when V_FSR = V_blower.

So no need to worry about your fan idling at low speed. Or at full speed.

Here's a theory about why some FSRs fail quickly while others last a long time ... a weak/failing blower motor will stress the FSR. If the blower motor spins slower than it should due to mechanical problems or increased internal resistance, then the back EMF will be smaller than it should be. So the current will be higher than it should be. So the FSR will have more energy to dissipate.

So if you keep blowing FSRs, there could be a problem with the blower, either electrical or mechanical.

Nice description. Clearly the FSR is solid state (and not just resistive) but like you I suspect that is has significant dissipation when running mid-load. If the motor was purely resistive and since P=VI, then the dissipation should remain the same over the whole speed range but the impedance of the motor is somewhat more complex than a fixed R value!

It's a pity that BMW have couldn't run the blower control like the aux. fan and tail lights (on the LCI models) and use PWM control - Class D if you like - but that would have made the blower motor more complex. And expensive. Like the aux. fan.

Such fun machines to own....