1999 SL 500 Blower Issue - Help Please!

[Woodsy53555]

My blower quits blowing after driving for a while. Last fall (for $500+) the dealer replaced the electronic control (in the dash), but that was actually a shot in the dark and it didn't work. The control on the dash shows the blower should be blowing full force, yet there is no air coming out anywhere after a while. It seems to happen after I've driven it for a while on the highway at 70 mph - about thirty minutes or so. I drove it for more than an hour at less than 60 mph without a problem the other day. It seems to misbehave intermittently, but mostly after driving on the Interstate. Has anyone else experienced this problem? Could there possibly be a damper of some sort that is closing at the wrong time when it heats up? A friend suggested some kind of solenoid mis-firing? (Bear with me, please, I am of the female persuasion and not at all mechanically inclined.) When I put the car in park and then start up again, the blower will start blowing full-force. It will also start up again properly after the car has been shut off. The car is going to the dealer on April 12th to see if they can figure it out, but I found this forum online and was hoping someone here could give me some suggestions. The dealer's next "plan" is to replace the blower motor, with no guarantee that it will fix the problem. I've gotten quite frustrated especially since I live in the Midwest and now is the time to be driving with the top down and the heater on! Of course, the dealer hasn't been able to recreate the problem! I told them THIS time I'm not going to shut it off OR put it in park ... before they see that I haven't totally lost my mind! Any possible solutions from this forum? Thanks much for any possible clues ...

[JimF]

same blower regulator, then here's a link for you to decide.
A/C blower's output is low . . .

[jjrodger]

Change the evaporator temperature sensor. It is a $50 part and a very quick repair. What is happening is this: the evap temp sensor has failed, so the evaporator ices up. You can be certain this is the cause by running the diagnostic cycle on the push button control unit. If the evaporator temperature shows a logically impossible value, usually about 40 deg C, then the sensor has failed. However, your symptoms are identical to mine. I am CERTAIN this is your problem. If you do a search of my past threads, you'll see the trouble I had with this.

[LeaUK]

Don't you just hate dealers taking a 'shot in the dark' approach! If JJ is correct (and I'm sure he is) maybe it's time for the MB dealer to write a credit note

Lea

[Woodsy53555]

The car has been at the dealer for the past two days now. They DID do the "harmonic balancer" recall service, which was nice; however, they couldn't get the blower, etc. to malfunction! I couldn't since Saturday, either! So ... the last call from them said that since we've already replaced the control panel and blower motor last year ... the mechanic "thinks" that the only natural next step would be to replace the regulator ... a $500 part. I'm thinking now that I'll just wait for the thing to malfunction again and then drive it to the dealer while it is malfunctioning (hopefully they'll be open then) and NOT put it in park so they can see what it is doing. I printed out everything everyone posted to my question and brought it with me, so I'm hoping they've checked out the evaporator temp sensor, etc. I'll ask again in the morning.

Someone in the tech forum offered the following:

"Same problem with my 99 SL 500
Took it to an indie A/C shop.the blower will work some times and then it would not come on at all other times,the mech. dug it out of the car, this thing is buried in between the engine firewall and the back of the dash below the filter assy under the hood.I have all the parts that were replaced and it clearly shows that the double squirrel cage plastic blower housing MB pn.A 129 830 01 03 .cracked around the (plastic) retaining clips allowing the squirrel cage to rub against the housing,evidently slowing or stopping the blower from turning depending on the selected fan speed.never heard any scrapping noise that will point this out so I was lost trying to diagnose it.This is not an electrical motor is an electromagnetic contraption that looks like the cooling fins on a motorcycle engine, this is activated by a control module another cooling fin looking contraption,BEHR 129 821 33 51,that burned up trying to keep the blower turning, This was $900.00 parts and labor with original equipment replacement and after examining this cheaply made parts that I will expect to find in a Hunday it a big possibility that you are having the same problems.GOOD LUCK".

I will mention that to the dealer in the morning. Getting rather frustrated, and don't really want to put any more money into "guessing"; but hate driving the car without proper air conditioning or heating.

Grrrrrrrrrrrrrrrrr.

[jjrodger]

I have attached a technical service bulletin to this post which is bang on point. I would change your evaporator temperature sensor before buying a $500 part on the basis of what the mechanic "thinks".

I'm pretty certain about my evap temp sensor diagnosis from your description of the symptoms. I took the car to the dealer several times and told them I thought it was the evap temp sensor and they just ignored me. Finally I went to a different dealer and told them that--among other things including the harmonic balancer--they were to change the evap temp sensor. They did it, problem cured.

My symptoms were as follows. I first noticed the problem on holiday in France where the ambient temperature was higher than at home. Running on the autoroute with the canvas hood up, the car was getting very hot. With the air con controls set to "AUTO" and 18 deg C, no air at all was coming out of the vents, although I could hear the fan running and the air con display suggested the fan was running at full speed. Switching the air con to "EC" mode would cure the problem, temporarily. About ten minutes after switching out of "EC" mode, the problem would recur.

These are the posts I made on this forum about my problem:

A/C diagnostics help

R129 AC problem

A good way to check for sure is this. Leave the car parked over night. Go to the car and turn the ignition on, without firing the engine. Run the self diagnostic routine on the air con pushbutton control panel and check the evaporator temperature reading. If the sensor is faulty, you will have a logically impossible value:

1. Turn ignition on (without firing engine)

2. Set the air con temp to 72 deg F or 22 deg C

3. Press "REST" for more than 6 seconds

4. The left side of the display will alternately display "01" (which is the test number) and the cabin interior temperature (eg 72 deg F or whatever the temp in the car happens to be).

5. Press the fan speed "+" button to advance to the next test (eg "02").

6. The evaporator temperature is test number "05". The working temperature of the evaporator is between 2 deg C and 12 deg C. Obviously, if your car has been left overnight and has not been started, the value returned should be consistent with the ambient exterior temperature. If the evaporature temperature sensor is broken it will return a logically inconsistent value, eg 40 deg C.

The part is a very quick and easy change. I would try it before spending $500 on something the mechanic "thinks" might fix it.

The other tests on the push button control unit are great:

01: in car temp sensor
02: outside temp sensor
03: heater core temp sensor
05: evap temp sensor
06: ECT temp sensor
07: refrigerant pressure meassured in BAR
08: refrigerant temp sensor

21: engine speed
22: vehicle speed

There are loads more.

[JimF]

Originally Posted by jjrodger

My symptoms were as follows. I first noticed the problem on holiday in France where the ambient temperature was higher than at home. Running on the autoroute with the canvas hood up, the car was getting very hot. With the air con controls set to "AUTO" and 18 deg C, no air at all was coming out of the vents, although I could hear the fan running and the air con display suggested the fan was running at full speed. Switching the air con to "EC" mode would cure the problem, temporarily. About ten minutes after switching out of "EC" mode, the problem would recur.

not been said by Woodsy is ". . could hear the fan running. . ". I agree with you that if it's running, then it probably is iced-up. If it's not running, then . . .

[jjrodger]

Originally Posted by JimF

not been said by Woodsy is ". . could hear the fan running. . ". I agree with you that if it's running, then it probably is iced-up. If it's not running, then . . .

I completely agree with you Jim, but she does say "The control on the dash shows the blower should be blowing full force, yet there is no air coming out anywhere after a while" and also that the problem is intermittent. I'd still try the cheap and easy part before the expensive and difficult one, especially when you can check my diagnosis by displaying the real values on the display for free.

[Woodsy53555]

Thanks JJ and Jim for the suggestions.

JJ -- I've printed out, once again, what you're suggesting and if nothing else will run the diagnostic test myself after I get the car home! I THINK I can handle that ... being a woman and all!!!!!!!!! Sure beats $500+

Might be a dumb question ... but, does it ice up even in the heater mode? Because my problem was occuring in BOTH heat and A/C modes.

[jjrodger]

Originally Posted by Woodsy53555

Might be a dumb question ... but, does it ice up even in the heater mode? Because my problem was occuring in BOTH heat and A/C modes.

The problem did not occur for me when running in economy mode. At all other times, whether trying to warm or cool the cabin, after 10 to 20 minutes no air would come out of the vents. In economy mode I understand the air conditioning side of the system is disengaged and it functions like a normal heater/blower.

In normal mode, whether heating or cooling the car, I understand the air conditioning side of the system is engaged. If the evaporator temperature sensor has failed it will report a temperature value of about 40 deg C, which is very high. The system will try to cool the evaporator when in fact cooling is not required and ultimately it will ice up. At least I think this is how it works.

[SteveA]

jj

You have also been a great help to me. Our '99 320 has the same problem so I followed your directions and the sensor came back with a value of 35 DegC.

Called my local main MB dealer and their service guy didn't know about those diagnostics!

Has anyone actually replaced this sensor - he's talking about having to vac down the system to replace it, surely not!

Car going in on Monday to be sorted.

First time on this forum!!

[LeaUK]

According to data for my '93 the evap sensor is B10/6 which is located behind the cover on bottom section below left of instrument panel (for LHD cars). This looks the easiest replacement ever. Simply remove this panel, unplug the 2 pin connector, withdraw and replace the sensor.

Doesn't get any easier than that!

Now if you change the evaporator that's another matter!

BTW - welcome to the forum...

Lea

[jjrodger]

These are the instructions on how to change the evaporator temperature sensor from Mercedes-Benz workshop information system. The part cost me GBP25 (about $40 at the present rate of exchange). It looks very easy. I have attached a diagram, too.

Cover on bottom section below left of instrument panel
remove.

2-pin plug connection
disconnect.

Evaporator temperature sensor (B10/6)
withdraw.

Temperature sensor
test, renew if necessary.

Install
in reverse order.