Urgent! W107 bypass for ACC Servo - PeachParts Mercedes-Benz Forum

meltedpanda · #1 12-23-2009, 10:34 AM

my buddies ACC servo split open I have 4 lines , 2 in and 2 out on the bottom, can I just connect them and still get heat? Which one goes to which one? Other options? this is a 1978 450sl

Urgent , he needs to leave thanks in advance

rowdie · #2 12-23-2009, 11:59 AM

I am not familiar with it but maybe you can tell fom the diagram on the EPC, page 10 of the heating section.

silverteam · #3 12-23-2009, 01:13 PM

Search in the forum and you will find the answer.

meltedpanda · #4 12-23-2009, 02:25 PM

got it!, two front are bypass for recirculator pump, two rear feed heater core. He is back on the road with full heat on or off, but better than not being on road. I guess in time he will decide if he wants to keep it this way ( not what I recommended) or get rebuilt unit

pop & blow · #5 12-23-2009, 02:32 PM

Here is what you do bypass servo all together, go to your auto parts store and get a manual heater valve , now where the heater core comes out of the fire wall put that manual valve in the line coming off the engine block to the valve this valve should come with a cable that needs to come inside so you can shut the heat off or on. if you just want heat bypass servo all together and make sure heater hose goes directly to the heater core and then back out to the engine. that should get you threww the winter,get some extra 5/8 heater hose for your bypass good luck.

lfausty · #6 12-08-2010, 02:54 PM

will this bypass also work out if blower isnt working and as well will the car defrost

my heat sourse now heated seat buttons and they do work!!!!!!! its single digits burr

meltedpanda · #7 12-08-2010, 03:28 PM

you will get some passive heat , but without blower motor ( fan) not much to do any good

Walrus · #8 12-08-2010, 05:01 PM

When bypassing the servo, hot water will no longer be flowing to the bottom of the servo. Therefore, the temp controlled vacuum "switch", mounted on the bottom will never close (actually, the vacuum switch opens, turning on vacuum to the electric switch, which closes), and the fan will not run in heating position. A vacuum source must be applied to the switch, or an electrical bypass be affected to allow the fan to run. Now if your fan is FUBAR, you will get a bit of air thru the heater cor with forward motion of the car, if you open the recirculation vents to allow outside air in to the cabin...

Fixing the sevo is a $600 or so proposition, replacing with rebuilt. Unwired Tools has a digital option for roughly the same cost, and is purported to work wonderfully. ScottinSoCal on the "other" forum has reported his retrofit, with desirable results, and no more worry about the servoc taking a dump in 2-4 years...