I assume you mean that you ground the blu wire and not the motor frame ??

If so, then you want to check the voltage at the yellow wire going to the regulator with key on and defrost position. That is full trigger for the regulator . With voltage there , the reg will complete the blu wire to ground , resulting in full fan.
If no voltage at yellow, Control panel is not sending the trigger to regulator.

Re-read post#8

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

Post 8 tells you that the CP show trigger voltage at the CP..it does NOT tell you if there is voltage at the yellow wire at the regulator.

The test is to check right at the regulator for 12v from red to blk and trigger voltage from yellow to black.
If he is grounding the blower motors blu wire and that gives full fan, then either the reg. is bad, the reg does not have proper feed , or the reg is not grounded.
Having the CP detect voltage output at the CP does not insure one has voltage at the regulator. Specially considering that he has already changed the reg and grounded the neg side of the blower, getting full blower.
My guess is the reg is not grounded...........but I would do the voltage check at the reg plug first.

I grounded the blower motors blu wire and that gives full fan
not grounded.

I do not have a voltage meter. I can pick one up, what do you suggest?

Then , where do I hook it up?

If you grounded the blu wire , you have by-passed the regulator circuit and verified blower motor and positive 12v feed... It is the reg that grounds the blu wire [ neg side of the motor/ a switched ground circuit] when the yellow wire gets a voltage sig from the CP.
So, a meter would be nice , or even a test lamp would help.
You are looking for bat voltage [ 12v] at the plug that goes to the regulator.
This will be the feed side of the plug, not the reg side.
This will be the red/blk wires ....
..then you want to see a lower voltage [approx. 6-8 v] at the yellow /blk wires when the key is on and the defrost position is set.

I am assuming you do have the new reg mounted???

True, but it's just one wire and odds are that the blower control voltage is there.

I wonder about the blower *and* the reg. . . . maybe the blower is not installed? Or the blower reg is not mounted on the blower?? That would be too funny.

It's not a "switched ground ckt" but rather a transistor action switch. Others may be confused thinking it's a "switch".

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

I am looking at the plug that goes into the regulator
There are 4 wires:
Red
Brown
Red/Grey
Green/Grey

Red and Brown reads 14.27 v
Red and Green/Grey reads 7.49 v

Did I do this right?

This is "Blowing" my mind!

Good one!

Just to make sure:
1) do you have the blower mounted in the car??
2) Is the blower reg mounted to the blower??

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

You know that and I know that.... but I am trying to get to the basics without getting technical on the guy.
OK??

For testing purposes, I want him to know the circuit is controlled/switched ON the GROUND side so he understsnds why the blower works when he grounds the blu wire.
I will let you take it ...

It is 19 degrees and snowing here.....

How do I test the new blower control unit? Everything seems to be okay until the wires go into that little critter

Actually, the 'switch' is an "analog" variety that is an variable attenuator with the regulator itself as the 'heat-sink'. Energy is either pass through (high speed) or lost in the regulator as heat (low speed).

Hope that's not too technical . . . but it's how the blower reg really operates.

Ok, Eric . . . if all is connected and you have verified that voltage from the N22 unit (in the dash), the blower should be on. The higher you set the voltage from N22, the faster the blower should run.

If all is connected properly, sounds like the reg is bad??

__________________
Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

It is a KAE Blower Control unit purchased from ******** AZ. Instructions say that "the surface of the blower control unit is pretreated with a very efficient proper amount of copper=heat=agent"

It seems like blower regulator is grounded, motor will spin when everything connected and I ground the blue wire. If I unbolt the blower regulator from the blower and ground the blue wire, nothing happens.

Any ideas????

First of all, thanks JimF for your information on A/C checks. They are very informative.
I have a 1995 S320 with 180,000 miles bought used that the blower would slow without cause and finally stopped blowing all together.
All sensor readings appear normal with step 8 going from 8 to 60 with fan speed dial min to max.
There were a couple DTC but I don't know from when they occured, I deleted all back to E000 to see if new codes logged.
It stayed on E000 for 3 days now. Did not show E001. Don't know if that is a problem or not.
I believe next step would be to check red to black and yellow to black voltages on reg.
Any suggestions welcomed.
Thanks again
Murf