Heater Control Gizmo
 

On the ole 81 380SL passenger side firewall, there is a gizmo there with 4 coolant hoses , a few wires, and a whole mess of vacuum hoses. Previous owner looks to have had trouble with it and bypassed it. The AC still works well. I picked up one from a 450sel, looks to be the same, have to check the PN on it but it had the same ac system(vertical buttons). I cut the vacuum hoses and wires a few inches prior to going into it to aid in hooking up the new one.

What does this do? Do the 20+ vacuum hoses connect to a plug so they dont have to swapped individually? Thanks

This is the infamous control servo. It varies the temperature and fan speed in response to changes in air temp and the setting of the temp wheel.

Do not mess with the individual vacuum hoses - there is a screw that removes the fitting that connects them all.

Do yourself a favor. Before you put it in, email george_murphy@compuserve.com. Pay him five bucks and get a copy of his troubleshooting guide so you can bench-test it to be sure it works.

If the servo isn't bad it will be....
 

The servo is probably stuck. They all go bad eventually. In time even the best metal-body rebuilds will fail. It's a genetic defect in the servo design. Even if you don't need heat fixing a dead servo will be a + because you'll get back all the fan speeds and the AC will work a lot better.

A rebuilt servo isn't very expensive and it's not hard to install. You can also get rid of the servo completely and upgrade to a digital controller.

Steve
380SLC
240D
300TD
E300DT