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Discussion Starter #1
So last week I'm driving (It's still hot here in Florida) and the LCD on the Climate Controller drops to 1 bar, then the fan motor cuts down to nothing....18 seconds later, it bounces back to all bars, and fan motor follows....OK...that's not good.

Couple of days later it does it again, 3 days ago, it started doing it every time I accelerate....same thing, down to one bar, fan follows then 15-18 seconds later back to normal....it was fine while idling or on the interstate...only upon acceleration....yesterday, everything works great...no issues at all.....This morning, it does it while on acceleration, hard braking, and driving on the interstate....a new trick this morning, while on the interstate the lcd stayed at all bars but the fan motor kept going to off....this would continue over and over, and one out of 8 times or so the lcd would flicker and go to one bar....

My mechanic states that all of the systems, blower, controller, baffles etc. are all tied together....last week he thought it may be a vacuum leak....I called him today and he thinks it may be the regulator or something on the blower motor.....I kind of figured it could be the controller....but I don't want to spend thousands trying to figure it out.....any ideas?

I think whatever it is, it's about to go anyways......as bad as it was today.

Oh yeah....1997 S500 Coupe
 

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I have never known the reg pack to go intermittent, the carbon brushes could be worn out on the fan motor and easy to replace
 

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93 SL500, 95 SL320, 96 S320, 98 S500, 2002 E320 4Matic Wagon & A little 91 5.0 FORD Mustang
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The brush thing is a great Idea.

Now make sure all the buttons feel the same as a sloopy or hard button may be the problem-that is an easy fix which may resolve the problem.

I'll have show you a process to fix a button.

I assume the display is like this?

Let us know what you come up with?

Martin
 

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Discussion Starter #4
So, an update to the issue. We had a cold front come through the area here on Tuesday, dropped th temp about 10-12 degrees, and dropped the humidity...still warm enough to run the air, but cool enough in the morning to try the heat.....absolutely no problems since then...I've put about 300-400 miles on the care without a single hiccup.
Works perfectly, I've even run it on max for 30 minutes at a time.....so if it comes back when it warms up, I know it has to do with heat or humidity. I ordered the blower regulator, and am holding onto it, I'm also thinking it may be the control unit...I know that heat can play tricks with weak or failing transistors.....that's my only guess right now, I will supply answers/clues as they occur....I hate problems like this, but am glad that right now I am on the positive side of the equation.
 

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So, an update to the issue. We had a cold front come through the area here on Tuesday, dropped th temp about 10-12 degrees, and dropped the humidity...still warm enough to run the air, but cool enough in the morning to try the heat.....absolutely no problems since then...I've put about 300-400 miles on the care without a single hiccup.
Works perfectly, I've even run it on max for 30 minutes at a time.....so if it comes back when it warms up, I know it has to do with heat or humidity. I ordered the blower regulator, and am holding onto it, I'm also thinking it may be the control unit...I know that heat can play tricks with weak or failing transistors.....that's my only guess right now, I will supply answers/clues as they occur....I hate problems like this, but am glad that right now I am on the positive side of the equation.
Actually transistors either work or they do not and never go intermittent, the switches can get poor contacts, but I think the tactile switches are used on these, dry soldered joints can be common. like on the remote fobs the tactile switches can get a leg that has come unsoldered or has broken off

When the carbon brushes are sticking or worn, often the incoming air can start the fan
 

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Discussion Starter #6
Actually transistors either work or they do not and never go intermittent, the switches can get poor contacts, but I think the tactile switches are used on these, dry soldered joints can be common. like on the remote fobs the tactile switches can get a leg that has come unsoldered or has broken off

When the carbon brushes are sticking or worn, often the incoming air can start the fan
So would the carbon brushes, affecting the speed of the fan, also affect the LCD bars on the display of the control unit? Also, would humidity affect the contact of the carbon brushes in the blower motor?

Thanks for your help so far....I probably won't know for sure unti lthe problem shows back up.....
 

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So would the carbon brushes, affecting the speed of the fan, also affect the LCD bars on the display of the control unit? Also, would humidity affect the contact of the carbon brushes in the blower motor?

Thanks for your help so far....I probably won't know for sure unti lthe problem shows back up.....
You have me thinking now,,, the speed in the display comes from the voltage output from the control panel, if the brushes are worn or sticking the display should still read out OK no matter what speed the fan is actually running at
 

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Discussion Starter #8
You have me thinking now,,, the speed in the display comes from the voltage output from the control panel, if the brushes are worn or sticking the display should still read out OK no matter what speed the fan is actually running at
That's where I'm coming from, the display at first dropped before the fan speed, and it would come back, followed by, again, the fan speed.
The day it was at it's very worst, and I was sure that it was going, the display was irradic, not always following the fan speed, but at times, looking as though it was "shorting out"....the fan was very irradic as well, since then, and after the cool front, no issues at all........which leads me to believe that it is possibly the control unit itself....not sure how the regulator would fit into that equation though.......
 

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That's where I'm coming from, the display at first dropped before the fan speed, and it would come back, followed by, again, the fan speed.
The day it was at it's very worst, and I was sure that it was going, the display was irradic, not always following the fan speed, but at times, looking as though it was "shorting out"....the fan was very irradic as well, since then, and after the cool front, no issues at all........which leads me to believe that it is possibly the control unit itself....not sure how the regulator would fit into that equation though.......
The regulator is fed from the control unit, so not that. the reg is fed from an all time live plus on 1 pin, 1 to ground, 1 to the fan and 1 from the control

I think that you have a dry joint now inside the control unit,, now if you open it up, one of the boards is attached by ribbon cables and these can break very easily, so take care in moving the boards around.

You could spray some non drying switch cleaner on the plug on the rear
 

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Discussion Starter #10
The regulator is fed from the control unit, so not that. the reg is fed from an all time live plus on 1 pin, 1 to ground, 1 to the fan and 1 from the control

I think that you have a dry joint now inside the control unit,, now if you open it up, one of the boards is attached by ribbon cables and these can break very easily, so take care in moving the boards around.

You could spray some non drying switch cleaner on the plug on the rear
Thanks for the info....I was kind of thinking the same thing....possibly a connection shorting out, which would explain the excelerating/braking issues....and may have something to do with humidity making it worse.....
 

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Thanks for the info....I was kind of thinking the same thing....possibly a connection shorting out, which would explain the excelerating/braking issues....and may have something to do with humidity making it worse.....
If your problem returns, the first thing I would do would be to run the test program to read the sensor values and see whether all of those are stable - although it sounds as though the blower control voltage might not be.

If, for example, the cabin temperature sensor were to send erratic values to the a/c controller, this would cause the controller to vary the blower speed in an errratic fashion. Observing the indicated cabin temperature via the test program would reveal this.

Mike
 

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Discussion Starter #12
If your problem returns, the first thing I would do would be to run the test program to read the sensor values and see whether all of those are stable - although it sounds as though the blower control voltage might not be.

If, for example, the cabin temperature sensor were to send erratic values to the a/c controller, this would cause the controller to vary the blower speed in an errratic fashion. Observing the indicated cabin temperature via the test program would reveal this.

Mike
thank you so much for the reply, I will try this soon.
I'm not a mechanic, but I tend to think like one.
The one key here is that it does it on acceleration 95% of the time, the one time that it did not do it under acceleration, it was extremely irradic, and I was quite sure that it was going to go out (I was actually hoping it would so I could isolate the problem).

The annoying issue has come back now....one question I have is a chicken/egg question. If the blower or regulator were defective, would that affect the LCD's on the control unit? The LCD's on the control unit always act before the blower does...meaning, the LCD will drop to one bar, then the blower responds, and when the LCD returns, Then the blower responds....I guess I'm assuming it's now a sensor or control unit issue because it is responding first, and not secondary......or does the lcd react to the regulator voltage as well?
 

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Discussion Starter #13
Two more small clues for you guys on this issue.
The one time on the interstate when it was very irradic, I caught the LCD bar actually flickering...but only a couple of times....
When you first start the car in the mornings, you used to be able to immediately adjust the climate control without waiting, now you have to wait about 20 seconds to adjust the fan speed, this is a new feature that mysteriously arrived at the same time.
Other than this annoyance, the car is running fantastic, but I will have to have this worked out by Spring, as I need my air to work 100% here in FL.
 

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thank you so much for the reply, I will try this soon.
I'm not a mechanic, but I tend to think like one.
The one key here is that it does it on acceleration 95% of the time, the one time that it did not do it under acceleration, it was extremely irradic, and I was quite sure that it was going to go out (I was actually hoping it would so I could isolate the problem).

The annoying issue has come back now....one question I have is a chicken/egg question. If the blower or regulator were defective, would that affect the LCD's on the control unit? The LCD's on the control unit always act before the blower does...meaning, the LCD will drop to one bar, then the blower responds, and when the LCD returns, Then the blower responds....I guess I'm assuming it's now a sensor or control unit issue because it is responding first, and not secondary......or does the lcd react to the regulator voltage as well?
I'm fairly certain that the blower control circuit is open loop: that is, the controller sends out a command voltage to the regulator and the regulator then powers the blower motor accordingly (or not, as the case may be). There is no feedback signal to the controller telling it that the blower is doing what the controller commanded. So I think you could have all the 'bars' showing on the controller even with a dead regulator or blower motor.

Also TTBOMK, there is no interaction between the level of vacuum - as affected by acceleration - and blower speed. The vacuum is mainly (solely?) used for HVAC flap operation and is supported when necessary by the vacuum line from the PSE pump under the rear seat. So, in any case, acceleration should only have any affect if the PSE pump is defective or the vacuum line to/from the switchover unit is leaking.

If you have some poorly connected or badly insulated wiring from a sensor that moves under acceleration then I guess this could cause your problem. As I suggested before, I would drive around with the a/c controller in 'sensor value display' mode and see what is going on with the various sensor values and blower speed control voltage when your problem shows.

It is also very easy to run the diagnostic test and see if any fault codes are showing.

Good luck,

Mike
 

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Discussion Starter #15
OK, just an update....I am having the car serviced in about 10 days, we are replacing the blower regulator then, as I have already purchased it. Yesterday I pulled into my neighbors driveway, it is a steep incline (we live in FL, no hills here), did not step on the gas, was actually lightly on the brake, the incline caused the lcd to back off and fan speed to drop. Did this twice...in a row. Today, hit a bump on the expressway, sent the control unit into a tissyfit.....lcd flickered (fan speed only), for about 5 minutes, no fan at all......then it eventually came back and was fine, until once again, hitting the accelerator a few times.....now it does it occassionally every bump that I hit....
Again, changing the regulator in 10 days, But I think I will go ahead and look for a good deal on a control unit out of a wrecked W140?????
 

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OK, just an update....I am having the car serviced in about 10 days, we are replacing the blower regulator then, as I have already purchased it. Yesterday I pulled into my neighbors driveway, it is a steep incline (we live in FL, no hills here), did not step on the gas, was actually lightly on the brake, the incline caused the lcd to back off and fan speed to drop. Did this twice...in a row. Today, hit a bump on the expressway, sent the control unit into a tissyfit.....lcd flickered (fan speed only), for about 5 minutes, no fan at all......then it eventually came back and was fine, until once again, hitting the accelerator a few times.....now it does it occassionally every bump that I hit....
Again, changing the regulator in 10 days, But I think I will go ahead and look for a good deal on a control unit out of a wrecked W140?????
Have you run the sensor and error code tests yet? Could be a waste of time, money and effort fitting a 'new' control unit if the problem's caused by a bad sensor, bad connector or bad wiring.

Mike
 

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Discussion Starter #17
Have you run the sensor and error code tests yet? Could be a waste of time, money and effort fitting a 'new' control unit if the problem's caused by a bad sensor, bad connector or bad wiring.

Mike
Forgot to add that, we are doing that when we service the car.
I will wait on the control unit.....thanks for the info.
 

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Discussion Starter #18
Have you run the sensor and error code tests yet? Could be a waste of time, money and effort fitting a 'new' control unit if the problem's caused by a bad sensor, bad connector or bad wiring.

Mike
Mike, thanks again for the advice, I've printed your comments, (hope you don't mind) for my mechanic....at this point, I think you're right and am leaning in the bad sensor direction....reason being: it has been unusually warm this week, I've found that the warmer the cabin temp, the worse it acts....if the cabin temp is 75 or lower, it doesn't act up at all, but if the temp is 85 or warmer....it reacts to it dramatically.
 

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It is so easy to check the output from the control unit, you do this on the reg pack. At the slowest speed there should be 0.08v and it goes up in 7 stages to 7.0volts when on max.
 

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Discussion Starter #20
OK...so it warmed up here a bit in florida, and this issue became more and more annoying...today we replaced the voltage regulator. Here's what happened. The problem is 99% corrected. I'm thinking I either have a short that weakend the voltage regulator, or I have a short in one of the connectors to the blower/regulator that we tweaked by replacing the regulator. The blower only cut out twice today, on a normal day it would have cut out at least 50-100 times.....so, my issue is still there, and this is how it originally started....which concerns me that it will return....that being said, it has to be in that blower box region.....is there a wiring kit for the blower/regulator that would replace all of the connections? Should I pull the connectors and spray a contact cleaner on all of them? Would a defective blower damage the voltage regulator causing it to slowly deteriorate?
 
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