A/C problem with w140 - PeachParts Mercedes-Benz Forum

MPM77 · #1 05-09-2004, 03:20 PM

Good day everyone-

Car in question is a 98 S500 with the activated charcoal filter (if that matters). The problem is that regardless of the selected fan speed setting shown in the LCD, the air flow does not seem to change. I stumbled across a website, www.continentalimports.com , that shows the three diagnostic tests that can be performed from the push-button controller. The three diagnostic forms are: (1) Actual Value- provides information on many different things including evaporator temp, engine temp, inside car temp, blower motor voltage, engine speed, heater core temp, refrigerant temp, vehicle speed, refrigerant pressure, battery voltage, etc. (2) Fault Codes - highlights any fault codes or errors in the system; and (3) Mode Activation - AKA Individual flap tests providing the ability to direct airflow to each outlet to ensure that the flaps are working properly. I followed the steps to enter each of these diagnostic modes, but was unsuccessful at getting into the Fault Code mode. However, when I was in the Actual Value mode I was able to see the voltage going to the blower motor, which I was able to manipulate with the fan speed control from low (.8 volts) to high (6 volts). Although the system showed that the voltage was changing with the selected fan speed setting, the air flow remained unchanged. What could be causing this? A bad blower motor? A faulty regulator? Some type of sensor?

While the article on continental imports was helpful, the examples were done using a 210 chassis E320, which for one does not have the activated charcoal filter. I found that in the Actual Value mode there were some additional functions that the article did not discuss that were shown when I was in the diagnostic mode. Also, I was not able to enter the Fault Code mode. Here's the method that the article said to do to enter the Fault Code mode: Turn on the ignition and set the left temperature to "HI" and the right temperature to "LO". Then, simultaneously press buttons "Rest" and "EC" for five or more seconds. All of this must be done within 20 seconds. The "Recirculate" button will flash its LED. The screen will then go blank, and the first code can be brought up by pressing the right "AUTO" button. When I completed this sequence, the system went into the Actual Values mode instead of the Fault Code mode. By contrast, the article states the following for the sequence for the Actual Values mode:
Turn on the ignition, press the "AUTO" button, set the temperature to 72degrees F (this can be done quickly by pressing both the red and blue arrows at the same time), then press the "REST" button for five seconds or until the left-side display reads "1". My summation is either the article does not give the correct sequence, I'm an idiot that can't follow directions, or hopefully the Fault Code mode does not come up if there are no faults in the system.

So can anyone answer the following:

1) Why isn't the fan speed changing with the control button?

2) How do I get into the Fault Code mode?

3) Does anyone have or know where I can find the Charts for the Actual Value code showing the normal values and the Chart for the Fault codes explaining what each code means?

My apologies for the long message, but thanks for listening and thanks inadvance for any advice that you may give.

Michael

jgl1 · #2 05-09-2004, 07:01 PM

With high fan speed selected, voltage supplied to motor should be > 6 volts. Check blower motor regulator.

Inspect cabin air filter; clogged filter reduces air volume available to blower motor.

FYI, W210 is equipped with cabin air filters and activated charcoal filter.

Do a search for JimF. Start with "A/C blower's output is low..." That will help you with the regulator. JimF also has a site which covers retrival and interpretation of W140 AAC DTCs.

stevebfl · #3 05-09-2004, 09:17 PM

You probably have a blower regualtor problem since you have found the proper actual value to check and the values were appropriate. other than doing the checks in real life at the regulator, that IS the test.

The test you found from my article came originally from the DM (diagnostic manual) and as you noted there are different instructions for every chassis and different actual values. The actual values set-up procedure is the same for all models although the values themselves vary.

I don't have a copy of the DM handy to look up the 140 fault procedure. I never use it so I don't have it memorized. I do it with the scanner if I see the need. If you have the time and wish an education you should pay the $18 and subscribe to the MB technical website for a day ( www.startekinfo.com ). The DM is there and rather easy to manipulate. The wiring diagrams are also there in color with links to Starfinder (parts locator), and other valuable references. Also through WIS.net such info as parts removal and theory of operation can be found, plus service bulletins.

#4 05-09-2004, 10:17 PM

MPM77,

Just in case you didn't pick up on it, you just got a response from the fellow that wrote the procedure that you followed. Read his signature.

Have a great day,

suginami · #5 05-09-2004, 11:36 PM

Quote:

Originally posted by LarryBible
MPM77,

Just in case you didn't pick up on it, you just got a response from the fellow that wrote the procedure that you followed. Read his signature.

Have a great day,

Yeah, miracle of miracles, Stevebfl is Steve Brotherton, who owns the shop "Continental Imports"

Peter Guenther · #6 05-10-2004, 08:44 AM

Check out this page for diagnostic help

http://www.k6jrf.com/MB_S500.html

MPM77 · #7 05-10-2004, 10:27 PM

Stevebfl, thank you for your help. Actually, after my original post I did some more searching through this site and I came a post from Steve where he mentioned that he was the author of the article on continental imports.

The blower motor and regulator were replaced in Oct 2003. Then, about 2-months ago I replaced the activated charcoal filter and in-cabin filter. When I replaced the filters I became skeptical that my indy never replaced the blower motor. The screws holding it in place were rusted and did not show any signs of being tampered with. That said, I'm thinking possibly the blower motor itself is to blame I've heard that the controllers themselves are known to have issues. However, if the actual values diagnostic is showing the changing voltage to the blower motor, then wouldn't that suggest the blower motor is the problem? Is there some other module that is to blame?

For now I am going to look through Startek info to see what I can find.

stevebfl · #8 05-11-2004, 08:25 AM

The voltage that you see from the actual value screen is not the voltage to the blower. It is the control voltage to the end stage amplifier that controls the blower speed - blower regulator.

If you view the blower regulator as a transister amplifier, the control voltage would be that which goes to the base of the transistor. The current carrying legs of the transistor are inserted into the ground leg of the blower motor.

Transistors can be used as gates or as amplifiers. In this case the transistor is being used as an amplifier. Higher voltage on the base translates to larger current flow across the transistor bridge. In effect it looks like a large variable resistance, resistor.

The original end stage was insufficient for the extended loads and the whole devise was redesigned in the 210 chassis (was the same in the 210 till 1998). it was never redesigned for the older 140 chassis. However, Behr has on its own redesigned the regulator and since we have started using them we have had no short term repairs. (high current in old blowers killed a few of the original design regulators in the warrantee period, for a period we).

If you look at the possibilities on fastlane you can see that the Behr is more money. I would definitely chose the Behr.

MPM77 · #9 05-12-2004, 06:59 PM

Thanks again Steve.

So is it safe to assume that the a/c controller is not at fault since the actual value screen shows the changing voltage? By your comments I would assume that it can be none other than a faulty regulator? If so, is there a way for me to test the actual voltage going to the blower motor? This way I can be certain before I buy the regulator.

Thanks

Michael

P.S. These questions may be or may seem redundant, but I am not too familiar with electrical systems and its terminology.

jgl1 · #10 05-12-2004, 08:11 PM

Using a volt meter, measure the voltage at the blower motor supply lines (colored blue and red) coming off the regulator. The regulator is attached directly to the blower motor case; access it by removing the blower motor cover panel and cabin air filter.

With the ignition on, voltage should range from 0 (AAC off) to approx 12 volts (blower speed set at max).

stevebfl · #11 05-12-2004, 08:58 PM

Actually the blower regulator is in the ground side of the circuit. Control is measured by the voltage drop across the transistor. If the base control is appropriate .5v to 6v and the drop across the regulator control can't get as low as 1v then the regulator is defective. When the blower is at low speed the drop across the regulator is in the multiple volt situation probably 6v or so. In Hi blow the drop across the regulator is in the range of 1v.