so I finally decided to tackle the dead blower fan issue in my 94 E420.

What the problem is:
1. Blower motor will not engage in any setting on the CCU.
2. The air compressor does come on and cold air can be felt from the vents if driving at really high speeds with the AC on.

what I did:
1. I took out the blower motor and tested it on the bench and it spun up smoothly and freely.
2. Suspected the blower regulator and bought one on ebay from potomac parts..replaced it and still the same problem.
3. Replaced all fuses in the fuse box and replaced the strip fuse outside the box.
4. Took voltage readings from the 3 pin connector. and I got...
0 volts from the red wire
variable voltage from the yellow wire (depending on which button I pushed on the CCU)
and a solid connectivity ground connection from the last pin.

5. I then suspected the CCU, so I purchased a rebuilt unit and it is still giving the same symptoms.

So NOW...what is my next step. Could the blower motor still be bad even if it worked on the bench

and why am I NOT getting 12 volts from the 3 pin connector?



my next step is gonna be to bypass the regulator by connecting the blue wire to ground...but ANY help is appreciated.

I love my benz.......my wife is complaining again........something about no time for her..or something....BACK TO THE GARAGE!!!

thanks in advance guys

I have a 95 e320 wagon and my blower motor also stopped. I haven't done all the things you tried - but did check the 30 amp link fuse and measured the voltages at the connector. I am also getting no voltage on the red wire and no signal voltage on the yellow wire. Keep me posted on what you find - I think our problem is no 12 vdc on red wire (?) - but I don't know what is causing it

Test Both sides of F15..they get hairline cracks that can not be seen.
If both sides have no power, then the suspect is ignition sw.
If one sid has power , it is the fuse.

__________________
A Dalton

Arthur -I assume by F15 you mean the 30A link fuse in a separate fuse holder next to the drivers side upper strut mount? I checked this fuse and it's ok - no hairline cracks and with ign switch on I get 12 vdc on both sides of fuse.

I also pulled the female side of the connector behind the brake vac booster on the firewall off and with ccu in defrost position and ign switch on measured voltages on this connector. On heavy gauge red wire it measured 0 - no dc volts - and on the lighter gauge yellow signal wire - same thing - 0 - no signal voltage. Does this give a clue to you about what might be problem? What is the source for the 12 vdc that is supposed to be present on the red lead? Is it through a relay or fuse ? Could OVP relay have anything to do with this? Other than no blower - ething else on my 95 e320 wagon is fine

The series chain for that red 12v feed at the X64 plug is ..Ign sw > R15 > X64 plug at firewall.

Key must be On to test Red @ X64.
Yellow comes from CC panel and that could be the CC fuse.

If you have 12v on BOTH sides of R15, then it is not the ign sw...suspect would be a break between R15 and X64.

You do not test the plug you unplugged..you test the one that comes from the cabin.............or better yet, you leave the connector plugged in and slip into the side of the terminals

Blk to red =12v
Yl to blk = variable V . according to CC setting

Key ON

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A Dalton

ok - thanks for clearing this up - i was testing voltages wrong - I'll test them with connector connected. If I get proper voltages then it's either the speed regulator or motor - correct?

You are propably testing the downstream line when you unplug....I want you to test the SOURCE ...If you leave the connector plugged in, you can't make that mistake.

Anyway, the Red/Yl/Blk go from there to the regulator/motor.

So, if you have power up at X64 for both red and yl, using blk for ground , then you have to go down to the blower compartment.
There you check the RED again for pos 12 v w/key ON..if YES, then you jumper a wire from the blu to ground..If Yes , then fan Motor is verified as OK..now see if you have yl trigger at Regulator..if Yes , then Reg is bad , if NO , you have a break in yl from X64 3 wire test connector up at booster.

That is why we use X64 for testing before going to blower .. Many guys tear right into blower/reg , when all is needed is a simple X64 test I mentioned.
The blower circuit uses a "Switched Ground" circuit...where the 12v feed [RED} of the blower is ALWAYS HOT w/key ON...the switching is done by the regulator on the GROUND SIDE of the circuit [ negative side]...and that is why if you ground the reg blu wire , you are by-passing the regulator.
BUT ..many guys do that jumper test and assume they have a bad regulator...but the yl trigger signal wire has to be confirmed FRST before condemning the reg. Without that yl variable sig from the CC, the regulator simply does not work...it has to be triggered !
Don't make the costly mistake of replaceinG the reg until you have verified trigger V at yl...............see it all the time... $300 WORTH OF PARTS AND 3 HRS LABOR FOR A BAD FUSE.

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A Dalton

thanks for all this info arthur - as soon as it stops raining here in MA and I can work under the hood again (no garage) I'll proceed with the tests - you provided me with enough info now that I am confident I can find the problem and fix it. Thanks again

Just a quick note as well, when you bench test the blower motor, it should VIOLENTLY spin hard and fast enough to jump out of your hand when applying 12v directly. If it gently spins up, the motor is probably shot.

Mine spun gently and quietly and seemed ok until I got a good one to compare to. Night and day difference, you can barely hold onto a good motor with two hands while running.

The reason to ground the blu wire in situ is so you do not have to take the blower out to bench test.
We do it right where it sits and I use an amp meter to verify draw at the same time.

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A Dalton

I have some of the same symtoms on 94 E420. My system will blow cold air when the car is first started. The compressor engages and after a few minutes disengages and then cycles on and off with the on cycle a few seconds and the off cycle nearly 30 seconds. The air is then warm (but not hot as when the heater is on). I haven't driven it on the highway to see if then gets cool. I've checked the mono-valve and it is OK. When first turned on the compressor pulls the low side pressure down into the normal region and when the compressor disengages it goes back high. Neither fan comes on at any point during the first 10 minutes of operation. I haven't left it on longer than that. Both the pressure switch and temperature switch on the drier measure nearly 0 ohms with the wires disconnected.

Sorry, blueboxgeek09, I don't mean to hijact your thread. I plan to go do the tests mentioned tonight but my shop manual is still in transit so I'm pretty much in the dark as to the schematic. If anyone has a pdf of fan control schematic, it would help me out immediately.

Click here for the electrical troubleshooting section of the factory service manual (FSM). Click the link for "Electrical Troubleshooting Manual - ETM", and be patient, it's a large PDF download (approx 75MB).

If the two fans in front of the condensor never engage, you either have a blown fuse, bad relay, bad switch, bad low-speed resistor, or bad fan motors. Pretty easy to figure out if you're handy with a VOM.

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

Thanks gsxr. I'm printing the lengthy document now. I have a good VOM so I'm hoping that I"ll have it solved this weekend.

Thanks again gsrx. I had the blower motor confused with auxilliary fan motors. The aux fans were not running in my car. The 15A fuse on relay K9 was blown. Replacing it got both fans running fine. I still have to figure out why my AC doesn't get cold. I'll start a new thread if I can't find an answer here in the forum.

blueboxgeek09, how how you coming with your problem? Hope that you have it solved by now. Thanks again for letting me get some advice in your thread.

After replacing the fuse on the relay, the fans worked but the AC compressor still cycled off after a few minutes of running and then only came on for a few seconds before cycling off again.

I used a VOM to measure the voltage at the pressure switch on the dryer while this was happening and found that it was the switch that was opening. I had previously charged the system using one of the pressure gauges that comes with a cheap charging kit. It showed the pressure in the normal region when the compressor was running. Because I was pretty sure the pressure was not low, I guessed that the switch was opening due to high pressure. After using an empty freon can to vent some of the freon into, the AC now works great. I vented freon until the compressor stayed on continuous with the temperature control set to full cold. My wife is happy as the temperature will hit close to 90 here today.

Don't trust the cheap gauges that come with the kits!!

blueboxgeek09, if there are any measurements you want me to make on my system for comparison purposes, let my know how I can help.