Blower speed slows at idle
 

I've run into a little problem with my 08 MCS convert, with manual trans. At idle with the blower in manual and at the max speed when I turn on the headlamps the blower speed definetly slows down ( about 500 cfm ). It does'nt matter if its on heat or AC. As soon as the engine speed goes above 1000 revs the blower speed increases. Took it into the dealer, 200 mi away twice, and they tested the battery and alternator and said they were fine. The service tech says that this is normal for these cars, but I'm not sure. Has anyone out there run into this problem.

I've got an 07 MCS and it doesn't do that. Blower speed remains constant whether in idle or rpms.
I think the it's normal answer is a cop out for alot of places that don't want to do a full diagnoisis.

Thats how I feel. I think that the alternator is not regulating like it should, but I can't prove it.

Sounds like under high load, the current is limited...
not realley a problem...as long as the alternator and battery is good, all is fine.
Ever notice at low rpms (idle) your lights may momentarrily change intenisty, when the high speed fan kicks on...same thing....
I am inclined to say why worry....sure you can be OCD about your car, but you spent all day driving to and from a dealer to have them look at this? I guess getting it checked before the end of a warrenty is fine, but just relax, and enjoy your car....i have seen this same phenomenon on other small cars...had a honda civic and a crx that did the same thing...

And please remember, the systems on a gen1 car and a gen2 are VERY different...so comparing them is like apples to oranges!!

Rans08Convert and mine are both 2nd gen's or were you just throwing that out about comparing 1st and 2nd gen's is different.

Have you tried hooking up a multimeter to it? (hook it to battery-I assume you know that).
With car turned off should read 12.5-12.8 volts.
Turn car on should be 13.8-14.8.
Still running turn on fan and lights, volts should drop at first then go
back between 13.8-14.8 volts.

I think that's the process.

Ran the experiment
 

Cranked the blower up to full, got a hurricane at idle or at speed.

Like yours, an 08 Convertible

05 Cabrio...My fan speed is constant no matter my revs.

R52=gen1
thought this said gen1/r52 cabrio talk...was hardtop 02'to 06', cabrio for another 2 years...(till 2008, yes a 2008 cabrio is a gen1). The cars with a SC in the s, or normal unblown tri-tec (same as the r50).
I tossed that out cause all the confusion in just using the model year of the car....sometimes noncabrio owners of the same model year chime in and cause confusion. If you post the same question in the right hardtop forum, there is much more ecperance, as the cars are the same except for the top, and some minor bracings, and trim parts.

Your hardtop is gen2....
the cabrio gen1 stayed in production till the end of 2008, confusing, but true.
That is why the platform monikers, ie, the r series is used in bmw terms....the r50, r53 (both till 2006)and r52 (cabrio, till 2008), are all gen1.

My bad. Man this stuff gets confusing.

No worries!! Happens lots. Heck you can't be faulted for trying to helpout another mini driver!!:thumbsup:

My R53 does this too.I never noticed it with the headlights,But blower slows down when opening windows.

Thanks for all the inputs. I have measured the air flow with a flow meter. With the engine at idle, blower at max output I get 2500 CFM as soon as I turn on the headlamps it drops to 2000 CFM. A big difference when your sitting at a red light in the middle of summer in the south.

Have checked voltages, but cant remember the exact numbers. I will recheck and post.

Hey even the dealers have trouble keeping them stright. I was in Memphis on business and stopped by to pick up a couple of oil filters. Told the guy that i had an 08 MCS convert. Got home (210mi away) and removed the filter housing and guess what wrong filter. Luckily I had not drained the oil yet. Called parts manager and he was great, next day shipped me two correct filters.

Thanks Should I post in another forum??

No, you are in the correct forum, I was the one that wasn't thinking. Sorry for any confusion.
I'm not familiar with the cabrio's not to mention 1 gen's in general.
But, seems like other have the same issue and call it normal for 1st gen cars.
Sometimes I wonder what normal is??????
Given all that, the multimeter reading should be correct for both gen's. (I think).

Gen1 mini's came with 3 or 4 different alternators..., cars with a SC, usually a denso, good unit. The non s got a veleo, a bit less robust, but decent. Depending on production date and how the car was speced, some cars got a different alternator (cold wether, heated seats?).
But in the end what DOES matter is ANY ALTERNATOR is limited in output....and a battery that has notfully charged will be trying to take a big chunk of the capicity...add lights, a big fan, then maybe ps pump....all loads that add up....voltage may drop a bit under high demand....this will sound like a motor speed change or look like a dimming of lights, and imo is expected a bit. A car with very low miles indicated the car sits lots....and this is hard on a battery...they are slowly discharged by nonuse, as by the electronics....
I bet when full charged, and driven lots, it may be less noticable. If it is extremely pronounced, it might be indicating a worn alterntor (brushes most likely). Since many aftermarket rebuildd are mostly junk (great warrenty, crappy parts), think closely before tossing a lifetime auto store one on in hope of getting rid of a minior annoyance.

Is a 20% decrease in air volume a minor annoyance?

I've got an 05 hard top that does the same thing... Got an 09 TSX that does it and had a Wrangler that dipped too... I'd say it's "acceptable".

You will also find the ac cools less at idle due to both reduced airflow, and lower compressor speed when the car is idleing and not in motion.