tomcinoz

I am doing a big service schedule on my 2004 500SL and making FCP Euro very happy. My car was originaly purcheased in London and then shipped to Australia in 2010.
The only problem the an iCarsoft scan has shown is a " HIVAC not communication with SAM module.... grounded or short circuit. The climate control and AC system is working perfectly.
When the rest switch is activated the blower motor starts and runs then turns of after 20 minutes os so automatically. I can hear the air duct flaps being activated so there is no problem there.
Howevet at the terminal of the auxillary water pump there is something strange happening. The correct wire for constant 12Volts shows a constant 12 volts but the terminal that the SAM unit should ground
to start the pump is showing + 3 volts when earthed to body. The original pump was not working ( thin terminal connectors corroded) and the new one is not working because of this SAM fault.
Wheater the original pump slowly seized and caused an overload that slowly overheated the connectors or it was simple corrosion, I don"t know. From what I have read SAM modules has some internal ceramic fuses
inside that can be replaced if need. Has anyone had a similar experience because I can not find anything on any of the many MB forums about this strange issue, other than many people now putting a 2 amp fuse at the pump
because it seems that MB failed to put a fuse in for this pump at the 12 volt supply side that had caused some cars to have the climate control completly destroyed.

bobterry99

That SAM fault code is either no longer active ("Stored") or in error, since you would have no A/C if it were active.

In measuring 3 VDC I wonder if you actually have a 12 VDC signal being switched to ground 75% of the time.

tomcinoz

Problem fixed. I cleared the fault code with ICarsoft and installed a new Bosch auxillary. Rest function works perfectly with an active working pump. My initial check of connector + volatage
was fine, but the postive voltage on the earth return wire certainly was a point of confussion for me. Feed back from earth line must be something to do with the way SAM units work. It's above my paygrade.
Now we have terrific heating for winter. If you think winter doesn't get that cold at some places in Australia you are in for a rude shock!

tomcinoz

Thanks for your reply bobterry99
Problem fixed. I cleared the fault code with ICarsoft and installed a new Bosch auxillary. Rest function works perfectly with an active working pump. My initial check of connector + volatage
was fine, but the postive voltage on the earth return wire certainly was a point of confussion for me. Feed back from earth line must be something to do with the way SAM units work. It's above my paygrade.
Now we have terrific heating for winter. If you think winter doesn't get that cold at some places in Australia you are in for a rude shock!

Cheers, Tom

tomcinoz

Forgot to mention. Also put a 2 Amp fuse inline with the +12 volt line to stop the AC system from frying out through pump motor going rogue.
From all the forums so many people have had the misfortune of their expensive climate systems wacked out because MB has no fuse for this 12 volt pump.
It seems the expensive climate control electronics became a defacto fuse by default.