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Old 04-07-2017, 11:33 PM   #1
Limit
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Join Date: Oct 2016
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Fan blowing full blast for a split second



Hope can get some advice.

I have recently noticed that the vent blowing full blast for a split second and then back to normal. Happened a couple of times already while driving on the highway.

FYI, electric coolant pump was recently replaced, but not the thermostat, not sure if it is related

Any help is greatly appreciated.
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Old 04-08-2017, 09:44 AM   #2
Blackedout95
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Final stage resistor? aka FSU Blower resistor etc mounted to blower fan. Controls speed, best place to check first.

Have you tried varying speeds to see if other fan speed settings are affected? If the FSU/FSR it would likely do it in park as well but symptoms such as where in the fan speed setting it does it and high or not at all vary from car to car.

Here is a video of a replacement on an E70 X5 I know you have an E71 but similar idea. The FSR is attached to blower motor as you will see.

https://www.youtube.com/watch?v=qiNe9rbgPe0


Outside of the obvious and common issue as mentioned above these damn things could have other issues which would involve more, lets put it this way hope its the resistor, easy fix.
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Last edited by Blackedout95; 04-08-2017 at 09:58 AM.
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Old 04-20-2017, 11:24 AM   #3
Mikey83
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does it happen when you go over bumps etc?
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Old 05-19-2017, 10:39 AM   #4
Limit
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Join Date: Oct 2016
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Quote:
Originally Posted by Blackedout95 View Post
Final stage resistor? aka FSU Blower resistor etc mounted to blower fan. Controls speed, best place to check first.

Have you tried varying speeds to see if other fan speed settings are affected? If the FSU/FSR it would likely do it in park as well but symptoms such as where in the fan speed setting it does it and high or not at all vary from car to car.

Here is a video of a replacement on an E70 X5 I know you have an E71 but similar idea. The FSR is attached to blower motor as you will see.

https://www.youtube.com/watch?v=qiNe9rbgPe0


Outside of the obvious and common issue as mentioned above these damn things could have other issues which would involve more, lets put it this way hope its the resistor, easy fix.
Thanks for the info, much appreciated!
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Old 05-19-2017, 10:40 AM   #5
Limit
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Quote:
Originally Posted by Mikey83 View Post
does it happen when you go over bumps etc?
No it doesn't
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Old 05-19-2017, 10:41 AM   #6
Limit
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I have started noticing a trend that the interior vent blowing full blast for a split second when:

1. Quickly accelerate to highway speed
2. Outside temperature around 10 celsius when inside temperature is set to 16 celsius
3. Fan setting is set to lowest

Could this really be the symptoms of a failing final stage resistor (FSR)?
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Old 05-20-2017, 03:23 PM   #7
Blackedout95
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Could be a voltage issue which again could be the FSR, is the signal interrupted and will a new FSR fix that, replace it and see. At this point and over the web it is the most obvious and cheapest start. If it was not the FSR and you truly have voltage issues tied to the charging system under accel and affecting the blower then youll be spending a good bit at a dealer to tell you why.

Honestly if you have a few tools and an hour or so give it a go.

If it doesn't solve the issue you will have to visit a shop, I know AC can be affected under hard accel at times due to the charging system, vac leaks etc but yours is simply tied to the blower fan speed so again hoping for you its just an FSR issue.
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