A/C Blower Surges Fast-Slow-Fast

[Gort]

When I start up my 135 and put the A/C on high, it frequently pulses in speed from fast to slower and back again over an over. It usually levels after 5 minutes or so. Naturally the dealer shop could not get it to happen. Anyone else have this? Resolution?

[aizdaman]

I have a 2012 135 also and my A/C unit does this as well. I am still trying to figure out if that is normal or not but I guess its either good or bad knowing that someone else has seen this too.

Maybe someone will confirm this for us.

[Pangloss]

I haven't seen this, but I've only mashed the MAX button a few times so far, and only for a few minutes. The rest of the time it's in auto set to 70F (where of course the fan speed varies as one would expect).

[RPM90]

Originally Posted by Gort

When I start up my 135 and put the A/C on high, it frequently pulses in speed from fast to slower and back again over an over. It usually levels after 5 minutes or so. Naturally the dealer shop could not get it to happen. Anyone else have this? Resolution?

The following is a rather long observation of something seemingly as simple as hot or cold air into the cabin:

The "auto" HVAC works.....in it's own particular way.
After driving my 135i for 2 years, I have come to experience and understand what it's doing, and what about it annoys me.
I've abandoned using "auto" in every car that has it.

I guess it's ok for those who don't want to adjust things themselves.
But, if you use it, you're at it's mercy and method of operation.

I use my HVAC manually, and it works to my liking most of the time, but it still has it's quirks.

To answer your question, no, I've never had my HVAC fan surge up and then down then up again.
But, I can see that happening in "auto" mode as it tries to give you the temp you want.

In manual mode, the temp setting should be used just like the old fashioned "cold to hot" control.
Adjusting the temp would then be simply adjusting that setting.
In "auto" mode, the temp setting is like your home thermostat, where you tell the system what temp you want, and the system goes about adjusting itself to give you that temp.

In manual mode, to cool/AC the cabin, set the vents you want air to come from.
Set the fan speed to how much air flow you want.
Push the "AC" button on.
Set the temp to it's coldest setting.
The HVAC will turn on the AC compressor to give you the coldest air it can. The fan speed will set the amount of air flow.
The vent setting will direct the air where you want.

If you want "MAX AC" all that will happen is that the system will turn on the "recirc" circuit, which shuts off outside air flow, and will recirc-ulate the cabin air. So, the cold air simply recirculates within the cabin providing a faster method of cooling the cabin air.
You'll also note that the air flow seems stronger, even though you may have set the fan speed to maximum in the first place.
That's because, once you closed the air flow to recirculate the cabin air, air flow will feel stronger as it's not drawing in outside air.

I don't use the "MAX" setting. To get max cooling I open the windows and sunroof to vent out the hot air while I have the AC on, fan at full blast, and air flow from the dash vents and floor vents.
I then start to drive to get the air flowing, hot moving out while cold air blows from the vents.
After about 3 or so minutes, I shut the sunroof, close the shade, and roll up the windows.
Once I get the cabin temp to my liking, I turn down the fan speed.

If it gets too cold, you can turn down the fan speed, which will flow less cooled air, but the blowing air temp will still be at it's coldest.
So, another method to turn down the coldness, is to turn up the temp setting. When you turn up the temp setting, that actually turns down the temperature of the air flow.

This is useful on cooler temps, like in the morning, where there is a lot of humidity, but the outside temps are not too hot.
Setting the temp at around 70F will give you less cold air flow, but it will still provide dehumidified air flow. If you want less cold air, turn up the temp.
On cold humid days, you use the same idea. Set the temp to something like 80F with the AC on. You will get warm dehumidified air flow.

In "auto" mode, the system does all this, but it sets air flow and then changes air flow along with air speed, the way it was programmed, which may not be to your liking. I don't like it, so I use manual mode.

In auto mode, let's say you have the temp set to 72F. You turn the AC on. The system goes into action, depending on how hot it is you may get maximum air flow, whirling noises from the vents switching the air flow. It may even go to recirc for the first 5 minutes, and once it starts getting cooler, you'll hear more whirring as the recirc goes by to outside air flow, and the vents change to alter where the air flows from.
As it gets cooler still, the fan slows down. Once you get to 72F, the air still flows, but the AC compressor will cycle down, and you notice that cold air is no longer flowing out of the vents. That's because the "auto" brain senses that the cabin temp is now at or near 72F, so it shuts off the compressor and cold air flow, and you get this sort of warmish air that smells a bit odd. That's outside warm air coming in.
So, as the cabin temp rises, the AC compressor kicks back on and cold air starts to flow again. Wash, rinse, repeat.
I find it annoying, nearly as annoying as this post.

In the winter/cold temps, the "auto" system does some other very fun things, like flowing cold outside air into your cabin instead of continuous warm air. WHAT? Yes. If you've set the temp to say 75F, you'll get hot/warm air until the system senses it's at or near 75F, and it will then whir and switch to cool air for a while until the cabin temp drops under your setting, then it will kick in the warm air again.

So, it does it's thing, and I understand why it does what it does.
I just don't like what it does, so I use manual mode, where I control what, where, and when.
I like the sense of CONTROL.

[Gort]

Wow thanks for taking the time to write all that, but I never use any AUTO settings. I think it's a computer electrical distribution thing that BMW will never acknowledge exists.

[amancuso]

Sounds like you need a new final stage resistor. (blower fan controller)

[bogart]

Or your battery is low on power... that happens to me sometimes with my Braille... if I put in my fully-charged stock battery, the fan smooths right out.

[FDM68]

I know in mine and most others if you have the filtration set to auto it tends to adjust as it detects outside contaminates.

[jbureau]

Mine does this same thing where it will surge a little higher and then quickly return back to a slower speed. I will have to try and turn off the cabin air filter and see if this issue no longer happens

[bluejaypanther]

hmm... cheyne-stokes respiration?

[Bill B.]

Mine seems to stop momentarily every once in a while when in auto, somewhat annoying. It does not surge in speed, though.

My e46/e85/e83 never did this. My blower on my e46 only surged when the final stage resistor went bad.

[dtwyim]

Originally Posted by bluejaypanther

hmm... cheyne-stokes respiration?

[zamboni]

Originally Posted by amancuso

Sounds like you need a new final stage resistor. (blower fan controller)

This was common problem on E46.

[RPM90]

Originally Posted by Gort

Wow thanks for taking the time to write all that, but I never use any AUTO settings. I think it's a computer electrical distribution thing that BMW will never acknowledge exists.

No problem, you're welcome.

BTW, I don't use "auto" either, that's really why I wrote that write up.
In auto mode the HVAC does some odd things.
Unfortunately, even in manual mode there are oddities that exist due to the system being designed to be run in auto mode.
It can be done, just takes some time to figure out the little quirks in manual mode, like how you can have the temp at 76F and it will still blow cool air instead of warm.

I've never had any surging in my system running in manual.
The only thing I can relate to surge is using the "max" AC setting, which is more auto than manual, so I never use it.

[The Transporter]

Originally Posted by FDM68

I know in mine and most others if you have the filtration set to auto it tends to adjust as it detects outside contaminates.

Yes.

I tested this yesterday. If you set the filtration button so no lights are on, it does not surge. If you set the filtration button so the left light is on, it surges. I did not try the other setting.