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Old 01-03-2012, 10:36 AM   #1
ode2joy
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Final Stage Resistor?

Ok, i've read lots of threads searching for a cure, and haven't found one with the exact symptom of mine, so here goes. I can control my hvac blower manually just fine, turn it up, it blows faster, turn it down, it blows slower. The problem i'm having is that it doesn't really react to AUTO at all. No matter what, if i set it on any temp, from 59 to 90, it just keeps on blowing at the same fan speed it was previously set to.
Does this sound like Final Stage Resistor? I read up on the heater control valve, but i have the same temps from all vents as far as i can tell, so i think i've ruled it out since the biggest problem there is usually cold air from some vents and hot from others.
Anything else i could check? I haven't checked all of my fuses yet or done much research in the Bentley, could it just be a fuse?

Thanks
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Old 01-03-2012, 10:46 AM   #2
jgold47
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Quote:
Originally Posted by ode2joy View Post
Ok, i've read lots of threads searching for a cure, and haven't found one with the exact symptom of mine, so here goes. I can control my hvac blower manually just fine, turn it up, it blows faster, turn it down, it blows slower. The problem i'm having is that it doesn't really react to AUTO at all. No matter what, if i set it on any temp, from 59 to 90, it just keeps on blowing at the same fan speed it was previously set to.
Does this sound like Final Stage Resistor? I read up on the heater control valve, but i have the same temps from all vents as far as i can tell, so i think i've ruled it out since the biggest problem there is usually cold air from some vents and hot from others.
Anything else i could check? I haven't checked all of my fuses yet or done much research in the Bentley, could it just be a fuse?

Thanks
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So this may not solve all your problems, but I was having some strange behavior last winter and this seemed to cure the problems. There is a temp sensor (the three slits on the front) that uses a tiny fan to draw air across the sensor. The fan can cake with dirt (and usually makes noise), but its also possible the sensor is compromised. there may be other ways to fix this, but I did it when I had my radio out, but basically you take out the radio, then pop out the HVAC module. On the back you will see the fan, its held on with a couple of small screws and pops right out. You can clean the fan blades, and perhaps give a quick squirt of MAF or contact cleaner on the sensor with a chamios tipped (qtip). What I think this does is a) get the airflow across the sensor better and b) cleans off the sensor for a better reading. In both cases, the Auto HVAC uses the ambient temp to control the fan, so if your getting a wonky fan on Auto, this may be your cure before getting into the FSR which sounds like its something different (loss of speed control)
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Old 01-03-2012, 10:50 AM   #3
jasonbimmer
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is your external temp sensor working.
also is your internal temp varying corresponding to your temp setting?
when you press Auto, does the fan speed say Auto and the actual fan speed go up and down corresponding to what it says on the screen?
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Old 01-03-2012, 10:50 AM   #4
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Thanks Jgold, i stumbled across that same problem/fix yesterday somewhere, but had actually forgotten about it. I'm gonna start there i think.
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Old 01-03-2012, 11:04 AM   #5
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is your external temp sensor working.
also is your internal temp varying corresponding to your temp setting?
question 1: My car doesn't have an external temp display. Yes, this is strange. It's a fairly rare 323 touring, and when i picked it up, i had been away from BMWs for a time, and i didn't even realize right away that it doesn't have the button to control temp/mpg, etc. at the end of the blinker! I hate this, and i have already read about how to add it.
So, my car DOES have climate control, and climate control cars have an exterior temp sensor for the system. I looked in my wheel well where the sensor should be awhile back, and of course, it was missing but the wires were hanging. I ordered one and reinstalled it but have not had any change in the behavior of the system. How do i test it without temp display? I'm sure it can be done with a multimeter somehow, but i'm not sure how.
question 2: I can't really tell yet. It does change some from cool to warm and vice versa, but i'm not sure how accurate it is. I do know that the defrost button works perfectly. If i need defrost or a blast of heat, the defroster puts out strong, hot air immediately.
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Old 01-03-2012, 11:07 AM   #6
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Quote:
Originally Posted by ode2joy View Post
question 1: My car doesn't have an external temp display. Yes, this is strange. It's a fairly rare 323 touring, and when i picked it up, i had been away from BMWs for a time, and i didn't even realize right away that it doesn't have the button to control temp/mpg, etc. at the end of the blinker! I hate this, and i have already read about how to add it.
So, my car DOES have climate control, and climate control cars have an exterior temp sensor for the system. I looked in my wheel well where the sensor should be awhile back, and of course, it was missing but the wires were hanging. I ordered one and reinstalled it but have not had any change in the behavior of the system. How do i test it without temp display? I'm sure it can be done with a multimeter somehow, but i'm not sure how.
question 2: I can't really tell yet. It does change some from cool to warm and vice versa, but i'm not sure how accurate it is. I do know that the defrost button works perfectly. If i need defrost or a blast of heat, the defroster puts out strong, hot air immediately.
come to think of it the external temp probably has no effect to climate control.
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Old 01-03-2012, 11:11 AM   #7
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come to think of it the external temp probably has no effect to climate control.
I have been told that it does but not sure how it does.
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Old 01-03-2012, 02:00 PM   #8
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it matches the external temp against a table that says somethign like 0-60 = heat 61+ cold. because there is a difference between 72deg in the summer and 72 in the winter. not sure exactly the mecahnisim and I dont think its terribly important, but somepeople will complain about not getting heat when its pegged at 140f when its missing.

Also, I think honestly, that the BMW HVAC system on these cars may be the most confusing thing I have ever dealt with before. I still dont get the 3 dots in the middle of the dash, and why its either too hot or too cold at all times....
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Old 01-03-2012, 02:11 PM   #9
ode2joy
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as far as i understand that, it's just an independent control for the center vents which blow on your head/face. I'm glad my BMW has them with this other problem, because it's helping me regulate temperature while i'm living with this other problem.
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Old 01-03-2012, 03:59 PM   #10
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FSU failure has numerous symptoms and maybe yours.

Not sure if FSU is completely separate from manual speed control or not...BUT I just had to replace the wiring connection block to the FSU. It was shorting and melted at 1 of the leads, causing a completely dead blower motor. In fact my reputable non-dealer BMW repair shop in Lehigh Valley, PA (nameless for now) was happy to suggest a $400 motor replacement after supposedly troubleshooting...which I luckily declined.

Depending on which wire is affected it may cause different results and maybe yours. This must be a frequent issue because the dealer readily had the replacement socket and wiring leads for the replacement. Just like the light meltdowns! There are several guide posts on getting to the FSU if you search. It's tucked to left of glove box. 20-45 minute disassembly to get to if your handy. The worst part is pulling out the right air duct. But a completely dead FSU may be the culprit. It's relatively inexpensive at $60-80. I haven't seen any fuses specific to FSU or Auto control. There's a relay and a fuse for the whole system.

Here's my E46 climate control experience. Hopefully helpful and direct:

1) Wavering fan speed in Auto: Changed FSU, resolved. But these seem to be temperamental 'cause my shop had changed the year before. Tip! Keep the wiring harness connected when pulling it out so you have something to grab on to.
2) In Cold mode the passenger side blows much warmer: Charged refrigerant, resolved.
3) With A/C mode on I had a tinny, metallic hiss from center vent area: Charged refrigerant, resolved. I was able to rule out any mechanical theories others had suggested by turning key to accessory position and turning fan on...silent fan operation. Only when the compressor was active did I get the hiss. Turning off the A/C mode also eliminates the compressor theory. Shop also tested for leak with refrigerant dye (supposedly).
4) Dead fan blower motor: shorted and melted connection at FSU. Replace connection socket and leads as needed. Careful! Some of these leads are hot even with the key off. Unfortunately on this one I went with the shops suggestion first and replaced the motor...$200.00+ VS. $12.00. ALWAYS TEST FOR POWER TO THE FAN MOTOR before a replacement! If there's no power it's not the motor.

Good luck,
Scott
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Old 01-03-2012, 11:23 PM   #11
ode2joy
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Scott, thanks very much. I will take all of that into consideration. I've already priced the FSU and looked at a couple of Youtube DIYs. For the moment, i've got too many other parts ordered so i'm gonna live with this for another week or two, but i am able to get heat, my manual control seems to work fine. I am also going to have my freon checked ASAP, i know from several other cars that it can also make things behave strangely, as you have obviously figured out as well.
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Old 02-09-2012, 05:21 PM   #12
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ode2joy: What is the verdict. Was it the FSU? I have the exact problem of the Manual working fine, but the AUTO not working?
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