No A/C Blower - 1995 W124 E300 Diesel - PeachParts Mercedes-Benz Forum

austxjr · #1 10-07-2009, 07:21 PM

My fairly new 1 owner (before me) 1995 E300 Diesel does not have any blower for the climate control anymore. Here are the symptoms and what I've done so far to diagnose/isolate the problem:

1995 W124 with OM606.910 diesel engine - 132,000 1 owner miles
Car still starts, idles and runs fine - A/C/Heater blower and recirc blower don't blow.
It did this a few times and then worked again, but has finally stopped working. Nothing happens when either of the fan switches are pushed nor when temp dial is changed... cold, hot, etc.. nothing.
SRS Light comes on shortly after starting engine and driving with A/C Climate control on - I noticed this the first couple of times the blower stopped working. Next time car started the blower worked until recently.
ABS light also sometimes comes on after a few minutes if Climate controls are turned on (blower switch - auto and both A/C and temp must be in position and compressor going).
Checked ignition switch and steering wheel airbag to see if they had any effect on SRS light - none.
Compressor comes on and A/C lines get cold fast - when switched to external air and driving on hwy, cold air comes in for a while.
I can hear the flaps opening and closing when switching between A/C modes. Fresh air does come in when proper switch is pushed.
I'm assuming blower is still good because each time it resumed working it ran just fine and the 30 A fusible link (or is it 15A?) to the blower is still OK.
Hissing comes out of A/C vents when A/C is on for a couple of minutes after start (I turn it off quickly so as not to damage climate control)
Auxilliary fans in front of radiator do not come on at all
I have removed and tested the OVP relay - it shows 0.51v when tested in diode mode - no rattles. I'm assuming it is good, though I may replace it as a precaution. I have not opened it up and checked solders yet.
Red light on recirculation fan switch comes on but recirculation fan does not blow either. I'm guessing that a whole circuit with both fans is turned off because of a over or under-voltage or current condition but if it isn't OVP then what is it?
When I drive on the Highway without the climate control engaged the SRS and ABS lights do not come on at all and when tested in a parking lot the ABS works quite well (no, I haven't tested the airbags for SRS and don't intend to do so).
I have acquired the workshop manual and schematics and am beginning to trace the issue down, but that is a big task.
Next Step: I'm going to have the alternator, battery and the voltage regulator tested and inspected to make sure that voltage isn't down below 13v. After that I will likely open up the fan housing and test the fan independently (and replace the motor if need be - replacement fan is about $90) to eliminate that possibility.
Thought 1: it could be one of the temp sensors going out, but there seem to be about six temp sensors and I'm not sure where to start or how to test them properly.
Thought 2: I hope it isn't the control unit for the blower because of price, but it certainly is possible, however, I'd like to eliminate all the other more common and less expensive options so any feedback is welcome.
I'll probably test some variations of having the Climate control on - does SRS and ABS only come on when cold/compressor are engaged or does it happen with heat and blower turned on?

I hope this is enough good info for those of you inclined or experienced enough to help with the diagnosis. If there is something else you want to ask, just let me know.

It sure seems like a voltage condition because of the intermittent nature at first and also the fact that SRS and ABS lights only come on when the climate control is turned on. Any hints, ideals or experiences that might bear on this would be greatly appreciated. I've already taken a bunch of pics to document the process of finding the OVP relay and testing it and will fully document the whole troubleshooting and testing process of getting the A/C blower working again (I'm currently an unemployed technical trainer and computer consultant so documentation for knowledge bases is what I do).

Thanks in advance for whatever informed feedback or info you can give me.

babymog · #2 10-07-2009, 08:32 PM

You might have more than one problem, but my first instinct is a belt causing low voltage.

If the lights are on in the dash, try the seat heaters or the rear-window defrost, ... the light will be on solid if there's adequate voltage, if the seat heater or rear-window defrost lights flash then it's indicating low voltage.

Check the belt for tightness, and look over the belt (feel it) for cracks and hard-glazed finish. Also check the tensioner, could be worn or seized at the bearing.

And of course check the voltage while the engine is running, if the belt seems okay and the voltage is still low then the next suspect is the alternator / voltage regulator.

If it's the CCU, I probably have a half-dozen here, I could be persuaded to thin the herd for a reasonable price.

JimmyL · #3 10-07-2009, 10:02 PM

This is what my issue was:

1995 E300 intermittent blower fan operation.....

Did you actually pull yours out or just look at it? Mine looked dead nuts perfect, but I loosened the first screw and it just jumped apart.

BTW, you should be commended on your trouble shooting and for the very informative and thorough nature of your post. It is a benchmark for others to observe! Nice job....

austxjr · #4 10-08-2009, 03:04 PM

Babymog and JimmyL, I'll check further and get back to you, Thanks!

I am a computer techie and have spent many years on the troubleshooting desk so I know how difficult it is to give an opinion without ALL the proper information. In past years I also worked on my MGB (engine, suspension and tranny rebuilds) and BMW 2002s. I hope I can help set a standard so the forums can be even more efficient and effective. After all, your expertise and time are valuable and we should all be thrilled so many experienced and knowledgeable folks are willing to donate their time.

I don't have seat heaters so that is out as a step, but the rear defrost was solid last time I checked. I'll doublecheck the voltage and belt again as well as the rear defrost. I will also doublecheck the 30A fusible link and examine it more closely by disassembly. What about the temp switch on the drier? Any ideas about whether that could cause these symptoms (compressor works, blowers don't) and is a likely culprit? These are the other possibilities I can see in order of cost and difficulty of service:

30A fuse (easiest and cheapest)
Check voltage coming off alternator and voltage regulator (serpentine belt too)
Temp switch on driver (don't know how to test - will research)
A/C/Heater controller in center console (trace voltage)
blower motor test
blower motor regulator replacement

Anything else?

austxjr · #5 10-08-2009, 03:44 PM

Did some more testing/troubleshooting and here are the results:

Checked 8A white fuse #3 for CCU - it is good
Tested the 30A blower fuse - disassembed - it is fine
Checked battery voltage - 12.6v steady with ignition off
Checked alternator voltage - ~13.88v with car idling or light throttle up to 14.2v.
Serpentine belt is in good shape and adjuested to proper tightenss
Dash lights are working when turned on and rheostat works fine.

I noticed something else that might play into this - the CCU is not lighted when the car lights are turned on. I assumed a bulb had burned out and that may be the case, but I'm thinking that it may just be a fault in the CCU. This is what i have to test next:

Climate relays - test. I think they are behind the fuse box, but I have to find out which ones for sure.
CCU - A/C/Heater controller in center console (trace voltages)
blower motor test
blower motor regulator replacement (I believe it is under the blower?)
Possible temp switch on the drier? or maybe other temp sensors?
I'm thinking of spending the $100 to replace the OVP and voltage regulator anyway - last and just in case, but it seems precautionary. Any thoughts?

After that I'm out of ideas except for what a trace of the voltages might turn up. Any other easy and obvious fixes I ought to test for first come to mind?

I guess I'll take some more pics and build a document that shows everyone how to go through this whole test cycle.

babymog · #6 10-08-2009, 04:04 PM

I don't typically believe in coincidences, so did you buy the car with these problems or did they start simultaneously?

The blower can be diagnosed using the 3-pin connector on top of the brake booster:

Remove the plug, open the plastic of the plug (for electrical access to the plug) and plug it back in, ... DON'T let the connectors slip out unless you've documented the placement!

Check (using a test light, not a DMM) for voltage from pin 1 to pin 3, with the ignition on in position 2 and the blower selector on automatic (center). Test voltage also.

Should get a light, and show ~ battery voltage.

Check with a DMM the voltage from each to ground, the brown wire (can't remember which one either 1 or 3) should be grounded, the other battery voltage.

Now check the voltage on the center pin with reference to a good ground. Press the low fan button and test the center pin voltage again, press the high fan button and the defrost button and test the voltage again.

You should see a varying voltage on the center pin based on which fan speed is selected, which indicates that the CCU is attempting to run the blower. This is all that you can do without removing the wiper assembly and blower cover to test voltage at the blower motor and see if it is the blower or the speed regulator "porcupine" below the blower motor.

If you did not get proper +12v, check for voltage at the strip fuse to ground. If not proper ground, wiring.

The ABS/SRS lights could indicate low voltage, but the rear-defog will trip and flash at a higher voltage so that is why I suggested trying the rear-defog. The Load-Reduction relay / OVP relay is the most likely culprit there.

Your A/C compressor will probably kick off if there's no blower, the freeze-stat on the evaporator coil will indicate too cold. Save that for last. It might never develop enough pressure to run the aux fans without some heat to the evap coil, especially if slightly low on R-134a. The aux fans run from the high-pressure switch on the receiver-drier and then through the resistor just ahead of the receiver-drier. The early ceramic resistors frequently failed, yours IIRC is a coil which is more reliable, but still could fail. Again, get the other problems fixed first as you can't troubleshoot the A/C without a properly operating blower.

austxjr · #7 10-08-2009, 05:01 PM

No, I don't believe in coincidences either. It didn't have any real issues when I got it. I think the blower problem is the only A/C problem I have - though I could be wrong. I didn't consider the bulbs burned out on the CCU a related issue (until now possibly) and it didn't get the SRS and ABS issues until the A/C Blower stopped working. The ABS and SRS don't come on when I don't use the climate control at all - so I think those have to be related not coincidental.

The A/C was working perfectly when I picked the car up. He detailed every little thing he knew wasn't perfect on the car and sold it to me at what the dealer would trade him for it - 3K for 132K one owner E300D - even with some A/C issues it is well worth it I think/hope. I was warned me that the A/C blower had shut off a couple of times for his wife and he thought maybe it was user error or possibly the temp sensor on the low voltage side of the A/C (turns out this model probably doesn't have that - only low temp sensor on high pressure side if I'm reading the forums right).

Even if the A/C wasn't working it was too good a deal to pass up. I got the car a few weeks ago from an old family friend who purchased a new E320 CDI BlueTec. He is 85 and his wife who has to drive him everywhere is 83 and they needed a new reliable car (they live on 400 acres in the country now) for her for the rest of their lives. She figures they have gotten 15 out of their '79 240D and '95 E300D and figure they can get at least 12 years from a new diesel Merc. I hope they are right - my E320 CDI was pretty trouble free for three years. I wouldn't like to troubleshoot a new one after 15 years though (this one is complicated enough). I doubt she will be driving until she is 95, but who knows?

I figured it had to be a good deal because it was a one owner always properly maintained and garaged. He and my dad bought identical (except for interior color) '95 diesels new in 1995 and had 240Ds before that. They were execs at UT and took excellent care of the cars, garaged, maintained at the dealer, etc.... He was mechanical and always had the service manuals. I have every reciept and the paper service manuals - though he couldn't get one for the OM606.910. My dad was totally not mechanical and just had the dealer fix anything that needed fixing. We sold that '95 in 2005 needing total A/C replacement - dealer told us evaporator was gone (though now I don't trust the dealer as complicated as these systems are and as much as I know they are mostly just parts replacers at the dealer). Even without A/C it should be a reliable driver for a couple of years - and I hope to get climate control working soon.

The A/C worked for a few weeks and then started having intermittent failures and only
completely quit working a two weeks ago. Fortunately after 69 days of 105°degree temps here in Austin the weather won't kill me without climate control. At least I have a couple months to sort this out before it gets cold (usually one fall cold snap and then teens and twenties in Jan and Feb.). This electrical troubleshooting is a real journey for me :-) Thanks for all the help/feedback. It will take me a while to get what you propose done, but I'll be back with the right info in a while - or possibly some pics and questions.

BTW, is the connector to test the blower motor way back behind the brake booster or the three prong on the firewall between the brake booster and the engine compartment? I'm thinking it is the one way back.

babymog · #8 10-08-2009, 10:56 PM

It's the one way back, beneath the windshield edge, and the wires run to the speed regulator under the blower.

Quote:

Originally Posted by austxjr

<>is the connector to test the blower motor way back behind the brake booster or the three prong on the firewall between the brake booster and the engine compartment? I'm thinking it is the one way back.

austxjr · #9 10-27-2009, 12:54 PM

Sorry it has been a while. I ordered a used CCU and spare used blower and am searching for the proper brushes now with no luck so far. Looks like my buddy (he's an ex-motorcycle racer and endurance pit crew guy as well as a firefighter who maintains the big diesel engines plus he maintains and pit crews for vintage exotics - just got back from Goodwood with a 1960 Ferrari 250GTB SWB and a 1958 Porsche RS60 - cool) and I may start rebuilding and testing the blower motors and diesel injectors as a side business - maybe anything else folks need as long as we can make $20 or $30 an hour for our labor and help folks out - that is better than the $100+ most shops charge just to swap new parts! He has an identical E300D he bought for $500 and resurrected from under a layer of 2" and 5 years of crud. Pretty damn good mechanic too - not just a parts changer.

I swapped the CCU and it made no difference. I think I'm mainly down to testing the blower and possibly the regulator as you have outlined and am taking pictures to document and trying to figure out the best way to get the blower testing done before removing my windshield wiper to get to the blower. From my additional reading it is appearing more and more likely that the brushes are just worn out in this TX car from running the A/C all summer long. So, it looks like this is the troubleshooting process so far:

- Compressor comes on OK so low temp sensor on high side is probably OK (replaced on car at 80K miles - whole A/C was rebuilt for $3K)
- Haven't really tested temp sensors through system yet.
- CCU operates flaps in system OK for fresh air and recirc.
- Checked OVP and it seems to be working properly
- Checked alternator voltage and voltage regulator and they seem OK
- Checked battery voltage (cars starts cold fine and voltage is OK so battery is fine)
- Replaced CCU with used working on and system operated same way
- Testing blower motor connection through regulator now

Thanks for all the help and I'll report what we find. This will be great info for a DIY article though I may have to develop a full diagram with all the elements in the climate system so this complicated system is fully understandable.

austxjr

ds190 · #10 10-28-2009, 10:18 PM

Is the ventilation blower for the interior temp sensor (aspirator blower motor) working? Put a 1cm x 1cm piece of paper up on the vent by the overhead light, and does it stay on it?

OscarG · #11 11-16-2009, 11:37 PM

Hi to all, I'm new in a MB (is my first ) and I'm new in this forum.
I have the same problem, I bought a 1987 300D TURBO with automatic trans. It has a lot of extras, electric seats, electric windows, electric sunroof, and with all electric extras a lot of electric bugs and troubles.
Ok, the A/C blower works only for a while, because there is a false contact or really bad contact inside the ignition switch, if you put the switch in a pre-glow stage, the blower is perfect, when you starts the engine the blower gone and never gonna get on again after you make a trick move over your key inside the ignition switch and the blower come on again.
Can post a schematics wire diagram for the ignition switch and A/C blower?
Thanks in advance.

lorenztl · #12 12-04-2009, 12:01 AM

My blower operates in a similar way. Turn the ignition key to pre-glow with the fan in high speed position it will run at high speed. However as soon as the car is started the blower fan shuts off. I've replaced the CCU and regulator on the blower motor and have the same result. Do you believe this may be an ignition switch defect?

compress ignite · #13 12-04-2009, 02:51 AM

It's in back of the Locking Mechanism (#5)and The "Tumbler" (#26 in the Cyrillic Pictogram)

Start here:
http://www.ps2cho.net/downloads/MB%20CD/W124/Main.html
(Almost everything)

GSXR's probably covered everything else:
http://www.w124performance.com/images/

First picture is from GSXR's collection it's the Blower Fan plug AFT of the Brake Booster.

Second picture is the Electrical Portion of the "Ignition Switch"
(Springs go Bad ,contacts get Boogered...Next thing you know the "Electricals" are a Crapshoot.)

Third Pictogram is of the Ignition Parts (Your Switch is # 11)from this Page:
http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=124133_501&M=603.960&GA=722.357&CT=F&cat=501&SID=46&SGR=105&SGN=05

#14 is the Vacuum Shut Off Valve for your Injection Pump.

Of Mercedes Benz Club of Russia's illustrated EPC.
http://www.detali.ru/cat/oem_mb1.asp?TP=1&F=124133_501&M=603.960&GA=722.357&

lorenztl · #14 12-07-2009, 11:44 AM

Quote:

Originally Posted by compress ignite

It's in back of the Locking Mechanism (#5)and The "Tumbler" (#26 in the Cyrillic Pictogram)

Start here:
http://www.ps2cho.net/downloads/MB%20CD/W124/Main.html
(Almost everything)

GSXR's probably covered everything else:
http://www.w124performance.com/images/

First picture is from GSXR's collection it's the Blower Fan plug AFT of the Brake Booster.

Second picture is the Electrical Portion of the "Ignition Switch"
(Springs go Bad ,contacts get Boogered...Next thing you know the "Electricals" are a Crapshoot.)

Third Pictogram is of the Ignition Parts (Your Switch is # 11)from this Page:
http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=124133_501&M=603.960&GA=722.357&CT=F&cat=501&SID=46&SGR=105&SGN=05

#14 is the Vacuum Shut Off Valve for your Injection Pump.

Of Mercedes Benz Club of Russia's illustrated EPC.
http://www.detali.ru/cat/oem_mb1.asp?TP=1&F=124133_501&M=603.960&GA=722.357&

Thankyou for the suggestion! I've ordered an ignition switch from Phil and will followup with you on the results replacing it. Oh boy!, appears the ignition switch will be a bear to get into and remove. Temporarily I've run a wire directly from the blue wire of the motor to a grounding switch in the cabin I can operate it with. I have to have heat!!

Thanks, Tom