Hello Everyone!

For the past month, I have been having troubles with my fans not blowing when the RPMs are above idle.

I emailed M.B.DOC and he said that it is possible that my battery is simply overcharged. The overcharged battery sends too much power to the fan blower regulator, causing it to shut down. This kind of makes sense in my situation. Here are the facts that point toward this diagnosis:

- We replaced the battery in the car in December, and plugged it into a trickle charger for 30 hours so that the battery wouldn't die as I left my radio on (so that I could recode it). I could have overcharged the battery here.

- I test drove my parents car again. In their car, it is when the RPMs drop to idle (or near idle) the blowers start blowing. I had it so that if I popped it in Neutral (which causes the RPMs to go up for some reason) the fans would shut off. Put it in Park, RPMs lower a bit, fans turn on. And I could do this over and over. I'm not a mecanic, but faster RPMs probably cause the alternator to spin faster, thus generating more power.

- So, now to test the theory. I turned on anything electrical I could find . . . (heated seats, rear defrost, cabin lights, bright lights, stereo), and took the car for a test drive. The fans never quit working! They blew hard the entire test drive. It would appear that the theory is correct. By turning on these electrical components, the power would be divided among the components and thus, less power will be sent to the blower regulator, causing it to function normally. I then turned off all the electrical stuff, and after a bit of driving, the fans eventually shut off again while driving and the problem returned. It probably takes a little bit until the battery charges back up to it's overcharged state. This may be just a fluke, but I guess I'll have to find out.

- Now, I never experienced this problem in the winter (with the heat blowing). This could possibly be because, in the winter time, we almost always used the heated seats, which draws a lot of power from the battery.


Now, my question is this . . .

- How do I find out if my battery is overcharged?
- If my battery is overcharged, can it be fixed?

Thanks for the help guys!
Bryan

A battery will not hold an overcharge.
First, you need a voltmeter.
With everything shut down, engine off, you should have a reading of 12.8 Volts at the battery posts
With the engine running and alternator charging, you could see up to 14.2 Volts at max. charging rate.
If you have more than 14.2 Volts, your alternator (Voltage regulator) is defective.
Easy and cheap to replace.
JackD

To check the battery, use a volmeter. It should be about 13.5-14V to work normally.
If it's too high, to discharge it, turn on your radio without the engine on. Check to voltage every 5-10 minutes. Don't let it be too low.

Hope this help

Thanks JackD!

Now, I am not too mechanically inclined . . . is the alternator a voltage regulator, or is the voltage regulator a part of the alternator?

I always thought that the alternator was an electricity generator for the car . . .

Can you tell me where I could find this part?

Thanks for your help!
Bryan

Oh, sorry . . . just answered my own question.

I see that there is a voltage regulator on FastLane for $41.76US. That's not too bad I hope that is my problem and not the blower regulator . . .

Regards,
Bryan

The only way to "overcharge" a battery is to place to high a back voltage on it. This can happen if the regulator is defective. Check the system voltage with the engine idling and accessories off. It should be 13.5 - 14.5 volts.

Rev the engine and it should hold in this range. If it goes over about 14.5 the regulator is probably defective.

A fully charged battery should measure about 12.6 volts at 80 degrees F. It's the higher system voltage that charges the battery. A battery charger works the same way. If an overvoltage is applied for too long the electrolyte can "boil" out of the battery.

Duke

Thanks for the input . . . I am definitely going to check the voltage tonight.

Is this voltage situation a common problem? Is it likely to be the cause of my air conditioning woes?

Also,

- I turn many electrical components on (heated deats, stereos, lights etc.) and the fans work fine

- I turn them off, the fan still works fine for five minutes or so, then the fans turn off.

Does this make sense that the fans still work for another 5 or so minutes? Is this because the battery still has to take time before it can build up to an overcharge again?

Thanks!
Bryan

From a physical perspective:

Jackd said it first...a battery will not hold an overcharge. It is designed to produce a nominal 12V at a certain rated current draw, period.

Because a battery will lose the ability to maintain the required current at that voltage for an extended period, the alternator is designed to replenish the battery and allow it to do its job while the engine is in operation.

The alternator is pulley driven, so the rate it will do so is dependent on engine speed.

By itself, the alternator is incapable of maintaing a steady voltage stream under varying loads...that's what the voltage regulator is designed to do. The voltage regulator is also designed to apply more voltage as load demands deem necessary.

When the voltage regulator fails, it either prevents the alternator from providing sufficient voltage or too much voltage. When the alternator fails, it simply does not provide adequate current.

When too much voltage is applied to the battery via the alternator/regulator, the battery electrolytes begin to boil. The worst case scenario will be a battery explosion!

When my regulator went out, the voltage was 17.5 at the terminals...the smell of sulphuric acid venting out of the battery caps was my first indication of a problem.

If you have an overvoltage problem, it can create a variety of electrical weirdness.

I don't know what year your car is, but the regulator is an external component on some alternators, and internal on others.

The internal ones are integrated and require alternator replacement...

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Wow, thanks for such a detailed response! I now know so much more about the function of an alternator

I guess I forgot to mention that the car is a W140 1993 300SE . . . I hope the voltage regulator isn't integrated

I checked on FastLane and it has a separate voltage regulator listed for my car, so I am thinking that it isn't integrated (fingers crossed!)

I will definitely check the voltage of the battery tonight when I see the car. It would suck to wreck the $170CAN battery that I just bought 6 months ago too

I haven't really had any other weird electrical glitches yet. The only thing is that the "Low Windshield Washer Fluid" hazard light is on, and it didn't go off when I added a gallon of fluid . . .

Thanks for your help! It is greatly appreciated! And if you know whether or not he voltage regulator is nitergrated on my car, please let me know.

Regards,
Bryan

Also, would a difference of only about 200-300 rpms be enough to cause enough power to shut off the blowers?

When in Park (400 or so rpms) the fans blow fine . . .
When in Neutral (700 or so rpms) the fans will not blow . . .

Thanks!
Bryan

The Voltage Regulator on FastLane

Attached Thumbnails

 

OK everyone . . .

I just bought a really good voltmeter and finally got around to testing the chrage on the 300SE.

Here is the step-by-step testing that I did:

- I have the fans set to full blast
- I drive until the fans quit.
- I slow down to stop the car
- As the car approaches the stop, the fans increase in speed
- The car is stopped and the fans are now blowing hard
- I pop the car in neutral, causing engine RPMS to increase by about 300 and the fans stop
- I check the voltage -- 14.2Volts
- I put the car in drive, RPMs drop 300, and fans start blasting again
- I check the voltage -- 13.8Volts
- I put the car in neutral again, engine RPMs increase, fans die
- I check the voltage -- 14.2 Volts
- Now, with the car in neutral and the RPMs still 300 higher, I turn on the heated seats, rear defrost, lights etc. Meanwhile, I am reading the voltage at the battery at the same time
- Voltage drops to about 12.8 Volts
- The fans start blasting

So it seems like, when the voltage is about 14V, the fans don't work. When the voltage is below 14V, the fans work. I therefore think that the voltage regulator is my problem.

Does anyone see an error in my logic? Should I go ahead and order a voltage regulator?

Thanks for your help guys!
Bryan