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1967 250 SL, 1965 300SE lang
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Discussion Starter #1
My climate control unit is beginning to fail in my 85 California wagon. I grabbed a used one at the junkyard and was lucky enough to get one that had been rebuilt 3 years ago. Yeah. I went to the website that sells the rebuilt units and they provide instructions indicating that you need to check to make sure that your aux water pump isn't frozen, as this would cause additional current draw and would/could eventually fry the climate control unit.

I have a CA car so I have read that the Aux waterpump is under my air filter (which is the front right corner of the car, not on top of the turbo like on non-CA cars) So when it is not raining I'll take out the air filter stuff and find the pump and check to see if it works.

My question is what do I do if it is a) unplugged or b) not working? Is this a rebuildable thing, expensive to buy new, just unplug, .... ?

thanks
Scott
 

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Premium Member
W-1-2-3 Go!
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16,161 Posts
You can try some things to determine if it's working or not.

With engine on, warmed up and heater running, open the hood and shut it off using the lever. Make sure you're in a quiet area, because you'll have to listen for the whirring sound coming from the auxiliary water pump. Does it run?

What CCU did you get - did it come from a W123? The W107 and W126 (first gen) versions are very similar but I think the 107 might not work.

You can also check if the connections on the aux water pump are good.

Install a 1A fusible link between the aux water pump plug and the vehicle harness. That way if it goes bad it will take out the fuse, not the climate control unit. DeliveryValve makes these (not sure if he still does, it's easy to make one). The 1A blade fuses are just hard to find.
 

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1967 250 SL, 1965 300SE lang
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Discussion Starter #3
With engine on, warmed up and heater running, open the hood and shut it off using the lever. Make sure you're in a quiet area, because you'll have to listen for the whirring sound coming from the auxiliary water pump. Does it run?
I like that. Means I don't have to mess with the air filter to see if it's running. Another thread I read said to connect 12 volts to the plug to see if it works but I think that requires removal of the air filter.

What CCU did you get - did it come from a W123? The W107 and W126 (first gen) versions are very similar but I think the 107 might not work.
EPC says that the CCU for a 123 is the same for all 123s with automatic climate control, and not common to 107 or 126 cars. So I got one from a 123. Part number is 123 830 12 85. It has a sticker from ProgRama (ProgRama Remanufactured Electronic Control Modules 2-3 YEAR warranty) with model numger 31285 on it and the corresponding MB part number, and a date stamp of 1st quarter 2007, so it's almost 4 years old. ProgRama's website indicates that they have a 3 year warranty, so it is out of warranty but I suspect the chances of it being good are pretty decent.

Install a 1A fusible link between the aux water pump plug and the vehicle harness. That way if it goes bad it will take out the fuse, not the climate control unit. DeliveryValve makes these (not sure if he still does, it's easy to make one). The 1A blade fuses are just hard to find.
Thanks. If the pump is working (if I can hear it with engine off and heater on) I'll probably do nothing except replace the CCU. If I don't hear the pump then I'll take out the air cleaner and do the other things to see what's up with it.

If the aux pump doesn't work, is this a big task / expensive task to replace it?

thanks
Scott
 

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Premium Member
W-1-2-3 Go!
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Looks pretty straightforward. Your aux water pump should be in the same location as the non '85 turbo models. The CA '85 had the air filter behind the headlight so the aux water pump should be right behind the air cleaner. The item under the air cleaner in your '85 would be the AC drier.



#101 has 2 hoses and the electric plug, plus the #104 mounting bracket.
 

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1983 300D
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Install a 1A fusible link between the aux water pump plug and the vehicle harness. That way if it goes bad it will take out the fuse, not the climate control unit. DeliveryValve makes these (not sure if he still does, it's easy to make one). The 1A blade fuses are just hard to find.
Thanks for the recommendation Pat. I do make them when requested to help out a fellow w123er or w126er who may have this potential hazard.

Here is tid bit of the fuse link in this thread.

1 amp fuse link for w123 Auxiliary Water Pump – Plug and Play! - PeachParts Mercedes ShopForum



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Premium Member
1967 250 SL, 1965 300SE lang
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3,063 Posts
Discussion Starter #7
No power getting to pump

OK, with car hot and running, temp turned to max, no power gets to the plug that the aux water pump is plugged into. I've already checked the fuses in the fuse box and that's not the problem.

What other points of failure are there where power to aux water pump can be turned off / on?

thanks
Scott
 

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1967 250 SL, 1965 300SE lang
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3,063 Posts
Discussion Starter #8
Never mind. I replaced the control unit (the things with the buttons) with one I got at the junkyard that had recently been rebuilt and now power is going to the wires to the pump. The pump is dead so I'm not plugging in the power to it. I have another pump that works that I'll put in as soon as I get a little fuse for it...
 
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