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Old 07-22-2013, 04:16 PM
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Doktor Bert Doktor Bert is offline
Das Sturm Uberdoktor
Join Date: Jan 2005
Location: Palm Springs, CA.
Posts: 2,670
Originally Posted by cooljjay View Post
Wrong! The number one cause of a failed acc II system, is a frozen aux water pump. The pump freezes and then it blows the amplifier behind the glove box liner.

The number two reason for the acc II not working correctly is the temp sensor tube that runs from the passenger side speaker grille to the blower assembly, with out this tube...the system cannot sample the cabin air.
The causes you listed are indeed issues with the system. The sensor tube (which can be replaced with hardware store water pipe insulation) will only cause the system to 'hunt' or switch between high and low blower speeds and/or A/C heat.

All the later model cars had an external fuse added to prevent a water pump failure from damaging anything. It is fuse #12 in the W123 ACC-II diagram.

However, the most prominent complaint I have experienced in 20 years of working on these systems is blown ACC fuses when the compressor switch is thrown, which everyone always blames on the servo.

Keep in mind the A/C compressor cut-out switch is power controlled and not ground controlled, hence a short will blow the fuses and seem like a bad servo.

I am the guy who fixed these systems when everyone else gave up on them...FWIW
Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013

100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership
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