I can tell that my heat is on - but only have a very low amount of air coming out of the vents.
After searching the archives and links I have done the following:

1) Checked fusible link on wheel-well and fuses in fusebox - all OK
2) Found three prong plug and check this plug for voltage between the ground and red, and then ground and yellow, with key "on", CCU in defrost and fan on high. I had no voltage readings at all (even checked the meter on the battery to make sure it was OK)
3) Does this point to the CCU? Is there any way to test this?

I do get heat and cold temp control with the temperature wheel, and you can hear actuators closing. But no fan.

As usual, any and all help is appreciated!

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John Gillespie
1988 560sec - 192k miles
2006 CLK500 - 40K miles
1995 E300 - 202k miles

Jumper the link fuse at strut tower..they look good , but have a hairline crack.
The test is to use your meter on each side of that fuse to ground..if only one side reads 12v, the link is open. [ KO]

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A Dalton

I just went back and tested the fusible link. There was a good healthy 12 volts on each side.
Given that, any suggestions for next steps?

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John Gillespie
1988 560sec - 192k miles
2006 CLK500 - 40K miles
1995 E300 - 202k miles

On the blower regulator, I am testing for the voltages between black/red/yellow wires on the female side of the plug (with the wires), not the side mounted on the firewall. Is this correct?

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John Gillespie
1988 560sec - 192k miles
2006 CLK500 - 40K miles
1995 E300 - 202k miles

You must check at the connector on firewall, not at the line that goes down to the blower,

good luck,
Acky

Acky has it correct ..the power comes FROM the firewall..
And the test is Red to Blk, not Red to ground..and Yellow to Blk for the variable V.........

If you have V at Red/Blk, but none at Yl/Blk, check fuse #7.

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A Dalton

Ok thanks - I should have said "neutral" not ground, but will check the voltages on the terminal mounted on the firewall. I probably can't get back to it until the weekend, but will continue on.
I appreciate the help.

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John Gillespie
1988 560sec - 192k miles
2006 CLK500 - 40K miles
1995 E300 - 202k miles

I will give you the series chain so you can diagnose after you take the readings.

The power goes from Bat + > Ign sw > F15/30 A. fuse link > to Red of firewall connector > blower +.
The yl comes from CP > regulator. That is reg trigger signal and is fused via #7.

If you have 12 v at red/blk and trigger at yl/blk at firewall, then the problem is down at the blower/reg.
Once there , you jumper a wire from the blu blower motor wire to ground. If that gives High Fan, the Regulator is bad.
Notice that the switching for the blower is done on the NEG side [ It is a Switched Ground Circuit], where the RED to blower is Allways HOT w/KO...
Grounding he blu wire from blower By=passes the Regulator, and therefor, that is the Regulator test. If no Variable V signal at Yl , then the reg will not trigger and No FAN can happen.

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A Dalton

I'm trying to diagnose a low blower fan regardles of ccu setting on my 1995 E420.

I have no power at either side of the strip fuse at F15.

Ignition Switch????

I have no ignition symptoms, so I don't understand. Is my diagnosis correct?

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RT


1984 300D---Sold
1995 E420 - 106K - Brilliant Silver Metallic/Orion Gray --- Sold
1984 300SD - 151K Manganese Brown Metallic/Mostly Black --- Sold
1982 240D - 79K - Manila Beige/Palomino---Sold

anyone?

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RT


1984 300D---Sold
1995 E420 - 106K - Brilliant Silver Metallic/Orion Gray --- Sold
1984 300SD - 151K Manganese Brown Metallic/Mostly Black --- Sold
1982 240D - 79K - Manila Beige/Palomino---Sold

Arthur...wanna come out of retirement for one more? LOL.

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RT


1984 300D---Sold
1995 E420 - 106K - Brilliant Silver Metallic/Orion Gray --- Sold
1984 300SD - 151K Manganese Brown Metallic/Mostly Black --- Sold
1982 240D - 79K - Manila Beige/Palomino---Sold

I might be wrong, but I don't think that the strip fuse is switched.

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Gone to the dark side

- Jeff

I assume you are testing with the ignition on, correct?

Sounds like a wire might be burned out, or maybe it is the ignition switch, but I would imagine you'd be having other accessory issues.

I would check for continuity between the ignition switch and F15.

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-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition

R-15 is Switched by buss bar 15X of Ign sw.
So, turn key On to Run position, put a 12v test lamp at Pk/Gn terminal of R15 and a good Ground . If lamp does not light , wiggle/turn key a few times while looking for a flicker at test lamp.
{I assume you are testing R/15 using each terminal and ground, not across the terminals}

15X Ign. is blower circuit feed specific on that chassis.

Your post is a little confusing. Does your post mean you do not have low blower or does it have low blower and can not be turned off ?

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A Dalton

If you hear the blower motor running, the problem could be a bad vacuum pod or two. To check them, remove the glove box and use an aux vac source on the lines that go to the vertical manifold (switchover valve) that runs vertically to the lower left of the glove box opening.