Aux. Water Pump takes out CCU - PeachParts Mercedes-Benz Forum

Brian Carlton · #1 12-25-2005, 07:14 PM

Well, I never did pay attention to the warning about the auxiliary water pump.

After finishing five months of work on the SD, it turns out that the blower does not function. After some meticulous checking, the controller is fine, the blower itself is fine and the resistors are fine. The only thing remaining is the CCU.

Remove CCU and pull the bottom plate to find some overheating within the unit. Not a good sign.

Replaced CCU and blower operates normally. But, I only run it for about 30 seconds.

I recall the caveat about the auxiliary water pump. I remove the pump and apply 12V to it from a battery while observing an ammeter. No rotation on the pump and 2.5A draw on the ammeter.

Replace pump and system operates normally.

So, a word to the wise:

Install a 1 amp fuse in the 12V supply to the aux. water pump. Someday it will save you the cost of a CCU. Wish I did,

whunter · #2 12-25-2005, 07:38 PM

Added to:
ShopForum > Do It Yourself Links & Resources > DIY Links by Parts Category
Climate Control:

Climate Control:

Cheap insurance.

The CCU is; $Oh $my $GOSH, $$$GASP $$$$$.

Not a happy price in my opinion.

Brian Carlton · #3 12-25-2005, 08:43 PM

Quote:

Originally Posted by whunter

Added to:
Added to:
ShopForum > Do It Yourself Links & Resources > DIY Links by Parts Category
Climate Control:
Climate Control:

Cheap insurance.

The CCU is; $Oh $my $GOSH, $$$GASP $$$$$.

Not a happy price in my opinion.

Thanks Roy.

It's an e-bay remanufactured unit. Price was $80. plus shipping. So far, so good.

Palangi · #4 12-25-2005, 08:59 PM

I dunno why us Southern folks couldn't just remove the pump and replace it with a bypass hose. I may just try that....

R Leo · #5 12-25-2005, 09:19 PM

Quote:

Originally Posted by Palangi

I dunno why us Southern folks couldn't just remove the pump and replace it with a bypass hose. I may just try that....

...or just unplug the stupid thing.

kmaysob · #6 12-25-2005, 09:22 PM

hmm ill have to add a fuse to mine and test my spare to make sure its good

Palangi · #7 12-25-2005, 09:51 PM

Quote:

Originally Posted by R Leo

...or just unplug the stupid thing.

Seems like I read somewhere that if you just unplug it, you have a blockage, therefore basically no heat. I'm thinking you could bypass it and still have enough heat for our balmy climate.

pawoSD · #8 12-25-2005, 09:58 PM

Quote:

Originally Posted by Brian Carlton

So, a word to the wise:

Install a 1 amp fuse in the 12V supply to the aux. water pump. Someday it will save you the cost of a CCU. Wish I did,

I am SUPER paranoid now, mine makes noises sometimes, I am buying a fuse holder and 1A fuse on Monday night!!!

and wiring it right in!!!

Especially since mine is acting flaky on occassion.

Brian Carlton · #9 12-25-2005, 11:46 PM

Quote:

Originally Posted by pawoSD

I am SUPER paranoid now, mine makes noises sometimes, I am buying a fuse holder and 1A fuse on Monday night!!!

and wiring it right in!!!

Especially since mine is acting flaky on occassion.

Getting to the wiring on the SD is a little tricky. I advise that you remove the battery. Just to the inside of the battery (toward the driver) there will be a plug. This is the plug for the pump. It unsnaps from a holder. Determine which is the 12V lead and put the fuse on the pump side of the plug.

You can't see the pump, or find the wiring to the pump on the SD without taking out half the plumbing between the two firewalls. Naturally, this would require you to remove the middle section of the forward firewall.

pawoSD · #10 12-26-2005, 01:12 AM

Quote:

Originally Posted by Brian Carlton

Getting to the wiring on the SD is a little tricky. I advise that you remove the battery. Just to the inside of the battery (toward the driver) there will be a plug. This is the plug for the pump. It unsnaps from a holder. Determine which is the 12V lead and put the fuse on the pump side of the plug.

You can't see the pump, or find the wiring to the pump on the SD without taking out half the plumbing between the two firewalls. Naturally, this would require you to remove the middle section of the forward firewall.

Been there done that

(we took apart our entire 83 remember) I have personally spent time with each and every part under there...

Here's something horrifying to look at, its the state our 83 is currently in (paint has been redone in this area and sway bar is gone however) The cord for the pump is clearly visible....

Its not all that crowded with everything installed, you can see the pump and plug easily...here's a pic I took of it before we began disassembly....

#11 12-26-2005, 01:21 AM

What exactly fries on the CCU?

Is it a little transistor looking thing or is it something else?

I just replaced a mosfet on my ham radio packet modem becuase of some shorting issues in the units past. Pretty easy fix, did it with spare parts, and worked nicely.

The CCU, although complex and small, is still just electronics. It can be fixed by able minds

pawoSD · #12 12-26-2005, 01:25 AM

Quote:

Originally Posted by Brandon314159

What exactly fries on the CCU?

Is it a little transistor looking thing or is it something else?

I just replaced a mosfet on my ham radio packet modem becuase of some shorting issues in the units past. Pretty easy fix, did it with spare parts, and worked nicely.

The CCU, although complex and small, is still just electronics. It can be fixed by able minds

I agree, I bet with some patience and labor one could replace the items on the CCU that get fried if the pump goes out. Just gotta be very steady with that soldering iron!

Brian Carlton · #13 12-26-2005, 08:46 AM

Quote:

Originally Posted by Brandon314159

The CCU, although complex and small, is still just electronics. It can be fixed by able minds

Well, Brandon, if you're up for it, I'll be happy to send you one for experimentation.

cbjukraine · #14 02-02-2007, 01:27 AM

Quote:

Originally Posted by Brandon314159

What exactly fries on the CCU?

Is it a little transistor looking thing or is it something else?

I just replaced a mosfet on my ham radio packet modem becuase of some shorting issues in the units past. Pretty easy fix, did it with spare parts, and worked nicely.

The CCU, although complex and small, is still just electronics. It can be fixed by able minds

Does anyone know the answer to this question? I have a very specific and strange problem occuring with my climate control. I'll try to explain it as best I can...

My climate control system works perfectly, almost. I have the shop manuals and have verified that I get hot air where required, when required based on the various settings that can be selected with the controls. The only aspect of the system not working properly is the footwell ducts do not open when the economy putton is depressed on a heat seating. The strange thing is that when I measure the voltage at the changeover valve (the two-prong plug) that controls the footwell ducts with a multimeter, I get the requisite ~12V. The voltage at the changeover valve is correct in all settings. That is, 0V when the footwell ducts should be closed and 12V when they should be open.

Does anyone have any idea how the voltage is correct, but the changeover solenoid does not engage in the economy/heat setting?

To add to the mystery, the footwell flaps do open (the solenoid does engage) when the multi-level button is depressed (next to the defrost). Just to add a little info, I recently discovered that my aux. water pump was not working. I removed and tested the current draw... none. A continuity check from the postive prong to the negative reveals an incomplete circuit. Is it possible for an aux pump in such a state to fry the CCU as previously stated?

Thanks for any ideas.

#15 02-02-2007, 06:58 AM

If an aux water pump draws more than 1.2 Amps, replace it. On the 124 CCU's if it is drawing more current than this it will indeed fry the CCU. I expect a similar result on late 123 CCU's.

Have a great day,