W124 blower motor issue

[WINGAS]

Long story short, via poor diagnostic procedures we now have a new Bosch motor and el cheapo resistor in our 1995 E300D. Blower motor simply stopped some time ago.

Before I rip into the center console to check the actual fan switch, I see there is a "climate control relay" listed under parts.

The A/C compressor does turn on when you put the CCU in defrost mode, but no fan.

I thought I had it reckoned as the resistor as the resistance between poles was in the millions of ohms.

Still no go. If CCU still actuates A/C, then CCU relay is OK>?

Are we looking at a new fan switch possibly?

HELP!!!

[WINGAS]

Well, I have the CCU out so I can visually inspect the fan switch. Test procedures, ya right.!

[sixto]

There’s a blower motor connector above the brake booster. IIRC it had a big red wire, a big black or brown wire and a yellow wire. The yellow wire carries a 0-7V signal to the blower controller. The red wire basically hard wires +12V to the blower motor. The black or brown wire goes through the controller and based on the yellow wire signal is PWM’d to +12V (off) to 0V (max). In short, check voltage at the yellow wire to see if the PBU is telling the fan to blow. Many of these cars have a dedicated 30-amp strip fuse for the blower motor outside the engine compartment fuse box.

Sixto
98 E320s sedan and wagon

[Sugar Bear]

IIRC the 30 amp flat metal strip fuse mentioned by sixto is on the left front fender well near the strut mount. It is a stand alone fuse under a black plastic cover. They often appear good but have hairline cracks. Jumper it or replace it to test it.

[WINGAS]

Tested the strip at no resistance, and it visually looks good.

Have the CCU apart and nothing looks odd inside, tested many connections ( went blind doing so) and the only iffy one is on the connector block on the fan side, where the 1st and 2nd pins seem to connect to a blob of solder right near them, except the 2nd one is "iffy". I am loathe to drop any solder on the board, but that the only weak connection I can find.

Thanks for the tip on the underdash /wall part of the wiring chain. More testing ensures..... its gettin' cold out!

[WINGAS]

So the fan switches, one of them anyway, feel wonky. No evidence of broken solder anywhere, yet I ordered up a CCU off Ebay. One number off, so I may have to yank the fan switch out of it. ( just earlier model than in our late year 95, which ends in 86, not 85. ) ??

One can only HOPE its the fix.

[Rick76]

Did you ever check the voltages at the connector above the brake booster?
Check for battery voltage between the heavy red and black wires. Push the defrost button and check for 6 or 7 volts between the black and thinner yellow wire.