Cabin Air Fan Speed Varies

drewmeister2 · Post by **drewmeister2** » 08 Sep 2018, 09:41

I've noticed that the speed of the cabin air fan varies intermittently on my 2009 S80, for no apparent reason (regardless of whether I'm accelerating, at idle, at a constant cruising speed, whether or not I'm recirculating air or taking in air from outside, whether using the A/C or heat). I've taken it in to the dealer (I have an extended warranty), and they found no trouble codes, so they didn't do anything. I replaced the cabin air filter, which did not help.

Anyone else experienced this? Also, I have a month left on my extended warranty. Do I have any basis for pushing the dealer to replace whatever part might be causing this, even without a trouble code?

Post by **abscate** » 11 Sep 2018, 11:04

It will vary according to heat load, solar load, speed of car - to maintain the cabin at the setpoint.

Does it vary if you set the fan button in the middle of the range?

Post by **oragex** » 11 Sep 2018, 11:07

Does it also vary in manual mode? P3 models have issues with the blower regulator www.youtube.com/watch?v=z-9SKu49LBE

drewmeister2 · Post by **drewmeister2** » 11 Sep 2018, 16:42

This is in manual mode, I don't usually use auto. It doesn't seem to matter regarding any variables. It will be normal speed, blow hard for a second (maybe half a second even), then go back to its set speed, maybe slow down for a second, then back to set speed, etc. This happens at all set speeds.

Post by **jimmy57** » 11 Sep 2018, 16:51

No noise? That is something I have seen with the blowers on those cars before they go out. Usually they make a high pitched squeal. I don't always hear the squeal but females do. Ladies have better hearing range than men.

drewmeister2 · Post by **drewmeister2** » 11 Sep 2018, 17:07

Yeah, no noise. My wife can't hear anything abnormal (other than the varying fan speed). I guess I'd like to know if anyone knows what might be the cause, but also, if I have any justification for demanding a new blower without any trouble codes. I guess it's hard to say exactly what to replace though without any trouble codes.

Post by **mrbrian200** » 11 Sep 2018, 17:41

Who would know this (I'm not sure)...

Is the output from the regulator to the fan motor high frequency PWM or true DC (variable)?

How to proceed would depend on this difference and whether you have access to either a voltmeter or oscilloscope depending. Voltmeter for DC, scope for PWM.

Post by **oragex** » 11 Sep 2018, 19:23

Also blow some air here or put the vacuum on it, it's the cabin temp sensor and may get covered with dust & stuff - don't touch it physically

drewmeister2 · Post by **drewmeister2** » 12 Sep 2018, 09:22

Yes, I've done that too, and it didn't help.

Post by **oragex** » 12 Sep 2018, 12:50

I would think blower regulator. Push the dealer for warranty before it's too late. It's a $1200 job. It won't give codes, but it's a very well known issue. Soon it will die and you will have no choice to replace it. Maybe try another dealer if not too far away.