Weird HVAC Blower Issue - Cycles on and off
 

All,


I'm having a weird issue with my Driver and Passenger (front) blower/fan for the HVAC.


When I first start the car (with the fan set to its highest setting), it will blow strong on its highest setting. While still on the highest setting, after 30 seconds or so, it slowly goes down to nothing. Meanwhile, the rear seat HVAC keeps blowing away strongly on its highest setting. After a couple minutes, it goes back up to full blast on its own, but only for 30 seconds or so and then decreases back to nothing. It is an endless cycle it seems. When I select defrost, same thing...endless cycle between full blast for seconds, then back to nothing for a couple minutes.



I've read that a weak battery can cause this as the computer reduces the fan speed to save battery (I find this odd because...doesn't the resistor block add in more resistors to lower voltage, thus still drawing amps???). My battery is newer and registered and coded to the car (90ah AGM). The battery is good as I'm reading over 12v with the car off and well into the 13v range while running.



The resistor block (final stage resistor) could be the issue, but I've read that when it fails that it either doesn't work at all, or, it allows the fan to turn on with the ignition off.



I'm wondering who has had this issue and what they might've done to fix it. Thanks in advance.

Not sure what you issue IS, but that is not my understanding of FSR failures. They can also speed up and slow down, uncommanded.

I’ve gone through 2 FSR, between the pair of failures, I have experienced all of the symptoms that many complained about.

BMW brand resistor is the only way to go. And make sure the harness isn’t fried. My definitely exhibited shorting and needed to be repaired, and dielectric grease was applied.

SOLVED
 

SOLVED

It was just the final stage resistor (FSR). I replaced it and it's working now.

Now on to a harder job: headlight lens replacement!

Just walked by the wife's X which has been sitting in my garage for about the past 6 hours. I heard a fan noise and looked inside the car. The blower fan was going on step 3 (3 bars were lit up), but the vehicle was off. Nothing else on the dash lit up. No key or fob in the vehicle. Should I be concerned?

It so happens that I have two spare FSR's on hand (although don't think that's what these things actually are in this vehicle), due to chasing this and other components as a red herring a couple of years back, when the problem actually turned out to be a battery with decent voltage but low capacity.

Probably has not much to do with it, but it's 79 deg F and 83% humidity here, "feels like" 84 deg F, or maybe even mid 90's in my stuffy garage tonight.

Someone tell me if this is an etiquette violation to jump in here a year later with my own problem, rather than starting a new thread. Just seems kind of tidy to me to put everything right here!

Got up this morning and checked -- the fan was still going. Tried to turn it down/off but it didn't respond. That was without the fob in. Inserted my fob (not the wife's) and noticed then the fan speed was on 5 bars, not 3. Don't know if I misread it before or if it changed when I inserted my fob. Anyway, with my fob in I was able to turn the fan down and then off. It stayed off after I removed my fob. If someone could explain some of this to me it would be appreciated! Thanks

explain what?



replace the FSR.

I'll take that to mean you feel chances are pretty good that there is no explanation for the weird functioning of the fan except that the "FSR" is fried. Thanks. I can do that. Just some more crouching under that dash for me. Guess I don't have to know why I was able to turn it off with the fob inserted.

ah, 'explain why the FSR - when they fail- seem to have a mind of its own and do weird stuff'




Cant say. they fail in strange ways- small perturbations in temp, voltage or load can cause them to react in different ways.


It is kinda a hallmark of a FSR failure. Other parts have an A>>>B>>>C>>D type relationship in their symptoms and failures, not fsrs.