My climate control system only blows hot air through the vents. The problem is that the CCU doesn't control the monovalve. The monovalve is OK, but doesn't get a negative signal from the CCU through pin L9. I had to wire the monovalve directly to the negative clamp of the battery and obviously this causes only cold air to blow
I've traced the problem to a burned out element - number IC6 on the
intergrated circuit of the CCU - but I don't have any diagram so I don't know what this element is, other than that it's a 16-pin element. could you tell me what this element is? anything to help me identify a replacement part? the CCU number is 124 830 02 85.

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1987 300E 185k miles

OK, here's a different approach to the same problem.
A couple of months ago the AC started blowing hot air all of a sudden. I traced the problem to the climate control unit so I found a used CCU on german eBay and bought it. The seller said it was OK but when I installed it in my car the exact same symptoms continued - hot air only. Now I'm waiting for another used CCU from eBay and my concern is this: is something in the car frying my CCU as soon as I put it in or was it just my bad luck that I had bought a used CCU with the exact same malfunction as my original one had? should I take the risk and install the third CCU and hope it will work or should I fix some electrical gremlin first so it won't get burned? what should I look for?

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1987 300E 185k miles

There is a possibility that the MONO heater valve is damaging the A/C control panel. You need to have the heater valve checked for "current draw" in Amperage. That valve should never draw more than 2A.

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MERCEDES Benz Master Guild Technician (6 TIMES)
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Retired Moderator

Thanks a lot! I'll have to check that. Could the aux pump also be the culprit here? Do you know what the current draw of the pump should be?

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1987 300E 185k miles

Hello,

My two cents worth.....

I have also tried to get schematic for the 300e climate control unit. I was told the last year for available schematics on this CCU was 1982, which I have a copy of. Call Schiff European Auto, 1/888.789.6882, they have schematics for Mercedes........ http://www.schiffeuropean.com/ However, not for the 300e/w124.


I have had exactly the same problem as you are expericing.

My solution was to get one off Ebay, and make sure you can return it ,if it doesn't work. A lot of stuff on Ebay is very flacky, leant by experience.

Then remove the Aux water pump [AWP]. Install straight threw pipe in its place. It dosen't make any noticeable difference to my heat. The aux pump can fry your CCU. Mine was leaking anyway. They are none fixable, mine wasn't amyway.

Second option go to http://www.programainc.com they have exchange units for around $235 with a 3 year warranty. There install instructions have you check the aux water pump before you hook up the CCU. It says no more then 1.5 amps draw on the AWP.

Its a bad design really I think, they should have installed a Aux relay to drive the AWP and the Mono valve. But i guess when its new it probrably OK!

Good luck

Brian

ok, maybe this is a stupid question but I'm going to ask anyway. should I check the current draw while the engine is running or does it make no difference? I checked the current draw of my AWP and it was over 2,5 amps measured while the engine was off. thanks.

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1987 300E 185k miles

The current is drawn through the CCU and causing problems inside when it draws too much - I was under the impression this faulty design was changed before the 300E was released, but apparently not. Why a 0.02 fuse wasn't included is beyond me.

John

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John Hughes, was in Landstuhl, Germany but currently in San Antonio, TX


1978 280CE Astral Silver now 59,xxx miles and counting "Silber-Kugel"
1986 300E Black Pearl Metallic 143,xxx miles 5-spd daily driver w/ blk leather "Schwarz-Schönheit"
1989 190E 2.6 (euro) 5-spd Desert Taupe 112,xxx kms Had to leave behind in Germany!!! "Helga"
1983 300D Pastel Beige now 312,xxx + miles SOLD

OBK#24

Yeah, I think I'll add a small fuse just in case. BTW, I unplugged the CCU when measuring the current draw and connected the AWP directly to the battery. The current varied from 1,5 to 2,5A and the pump turned then stopped then worked again and so on.

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1987 300E 185k miles