One more variable to consider. On my W123 300D the intermittent ACC failure turned out to by the electrical portion of the ignition switch. My ACC system would fail occasionally in very hot weather, like 100+F and humid in AK one day. By accident, I discovered that turning the key slightly to the left would cause the system to come back to life (BTW, my ACC had already been replaced due to an unrelated problem). Replacing the electrical part of the ignition cured the problem.

I think I just won the 2007 Silver Dildo Award...

I called the guy in Atlanta about rebuild CCU. He asked what problem was, so I went off into my mathematical equation about how blower works when cold, not hot ect...

He said that doesnt sound like CCU...so I started thinking...

I dug into the wiring schematics tonight, man I love those. 5 1/2 beers later I came across an interesting tidbit. The blower motor has an auxillary 15 amp fuse. It sits just fwd of the main fuse box (on my 87, anyways). I know all about this fuse because I replaced it once. I replaced it once because I connected a new aux water pump into it so the aux pump would run with key on (this was for veggie oil install, I wanted coolant running to tank easier).

Apparently, and in my infinite wisdom, I used washers to tie down the leads to the fuse that were somehow not totally conductive. They look metal an all, but who knows what Home Depot sells out of Taiwan. Apparently, with they are not very conductive over about 90F. WTF>!@#

Long story short, I removed the washers I had on the strip fuse, and voila. Blower motor works just fine, and so does CCU.


Anyone want to buy a rebuilt Programa CCU for 87 300D, still in box never even plugged in? Paid $250, will take $200 incl ship anywhere in US.

__________________
Paul
Benz-less
I need an SDL !

The "thermal intermittant" problem appears to be what I have....the CCU will turn on compressor, but no blower....guessing the solder joints between the main board and the blower controls is cracked....
I will try the new CCU (should get here tomorrow - hot in Houston) and let you know.
Thanks

Are you talking about the fuse box under the hood or in the passenger foot well.....I have a 560SL...so fuses are in weird locations!
BUT if this is a fuse, it will make life easier.
Did your CCU ever partially work? Mine will turn on compressor, but no blower.....
Does anyone know if the 560SL (1987) has an auxillary blower motor fuse?

On my 87 300D, there is an "auxillary fuse" for the blower motor, and its located directly in front of main fuse box at drivers side, back of engine compartment. I also checked the wire diagrams but no 560SL was listed. The other models it listed also show aux fuse at this location, so its worth a look. Im not quite sure why mercedes felt it necessary to use a strip fuse for their 30 amp blower motor fuse, but they did, and its not all that reliable or readily available. (this is me, trying to pass blame for easy fix)

__________________
Paul
Benz-less
I need an SDL !

and yes, my CCU worked except for sporadic function of blower motor. IT was all because of poor contact to the blower motor strip fuse.

__________________
Paul
Benz-less
I need an SDL !

Got the new CCU today and success!
Installed and blower works great.....side note, the air flow (which didn't work very well) now works exactly like it should.
For $135 I would try this before taking to mechanic......
You can buy the rebuilt CCU (which looks BRAND new) from The Benz Store. $135 + $45 core charge and shipping.

Glad to hear about your success, the best thing about the results for everyone but yourself is that you posted the final outcome for future searchers. Too many folks don't record what finally took place and that leaves everyone hanging.

Tom

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1993 300TE
1984 300D
1984 300SD
1976 BMW R90S

I have the intermittant blower problem but usually I just push a few buttons and it comes back on. However, after getting my AC system repaired last summer, it won't turn off. I just unplugged it at the compressor for the winter, but that's a little inconvenient to do every time I get too hot or too cold.

If I leave it plugged in, it runs continuously (as in, the clutch never disengages), the whole line freezes and the vent flaps stop working. My temp setting on the climate control functions and I know this b/c the auto fan setting ramps up and down to maintain cabin temp, but it doesn't succeed at cutting out the AC compressor when cooling is not needed. Any ideas?

bozeman, what car are you having problems with?
is it also an 87?
John

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

My '87 would turn on at random, cyclilng the switch to ECON and back off would turn off the fan and compressor. I replaced the ACC unit, all is well. I also unplugged the aux. pump just in case it was the reason for the ACC failure the PC board on the old unit was discolored from heat. Will check the aux. pump as time allows, it's spring and it isn't top of the list.

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Gone to the dark side

- Jeff

I have an 87 300D as well. I'm pretty sure the econ button doesn't cut out the AC but will double check.

Yes, that is the function of the ECON button, it is supposed to disable the A/C compressor. If it doesn't ... you've likely got a bad CCU.

__________________

Gone to the dark side

- Jeff

My old acc wont shut off either - ac comp runs all the time regardless of temp wheel settng. Still get heat, just always get a/c, which aint a bad thing in Georgia. Perhaps this is karma, from all the years driving rabbit GTIs down here with no a/c. I noticed if I push and hold the off button on Acc, it shuts off, but as soon as I let go it comes back on, even with off pressed. Im sure this is acc related problem, oh well. Not worth it to fix just that.

I returned that rebuld acc unit, too, since I didnt need it. Put money into rebuild cruise amp!

__________________
Paul
Benz-less
I need an SDL !

If you end up pulling the zebrano panel over the CCU, I'd be interested to know if it is the non-Bosch (two silver tape squares) unit.

__________________

Gone to the dark side

- Jeff