Auxiliary Water Pump Can Destroy CCU or Even Car? - PeachParts Mercedes-Benz Forum

mbboy · #1 01-29-2019, 09:12 AM

The auxiliary water pump on my 81 380sl hasn't been working, so I just picked one up on Ebay. However, I learned from several threads on these pumps that, if the pump seizes and draws too much current, it could destroy the CCU or even the car, as it did in this thread:

I lost it all....electrical fire high up in the dash

So, I'm hesitant to install it without first putting a 1 amp fuse on the power wire out.

Can anybody tell me if that problem affected the 81 380sl and, if so, is it caused by particular pumps, the car's circuitry, or both.

Thanks very much in advance. __________________
1981 380SL
Chassis: R107.045

Diseasel300 · #2 01-29-2019, 09:18 AM

It affects all cars with the ACCII climate control system. 1980/81-1985. It's due to a design flaw in the pushbutton unit itself. The traces are not heavy enough to carry locked-rotor current to the pump and can overheat to the point that it damages the pushbutton circuit card, or if you're really unlucky, cause a fire. An inline fuse in the positive lead to the motor is cheap insurance.

mbboy · #3 01-29-2019, 09:51 AM

Quote:

Originally Posted by Diseasel300

It affects all cars with the ACCII climate control system. 1980/81-1985. It's due to a design flaw in the pushbutton unit itself. The traces are not heavy enough to carry locked-rotor current to the pump and can overheat to the point that it damages the pushbutton circuit card, or if you're really unlucky, cause a fire. An inline fuse in the positive lead to the motor is cheap insurance.

Thanks a million for the quick reply.

I replaced the "evil servo" with the digital unit some time ago, but your reply suggests that it won't make any difference.

After looking on line for a 1 amp fuse and fuse holder, the only one I could find was this one at Advance Auto parts:

https://shop.advanceautoparts.com/p/littelfuse-in-line-fuse-holder-0fny0030xp/11499021-P

I guess I can solder that into the power (black?) line. Problem is finding a 1 Amp fuse. Any ideas?

Mxfrank · #4 01-29-2019, 04:09 PM

Depending on the vintage of the CCU, there may be a fuse conveniently located on the rear of the head unit. All you have to do is pull the dash apart to get to it. An inline fuse would be a good idea.

mbboy · #5 01-31-2019, 06:40 AM

Thanks for the info. Yes, putting a fuse in would obviously be preferable to taking a chance on there being a fuse in the head unit or, even, having to check for one.