change over valve repairable? why not?
 

Has anyone opened one of these up to see how it went bad and repaired it: part # 0008000478?

Switchover valve. Supposedly you can clean and reuse. Gets clogged up with smoot? Not sure.

This is basically a 3 way vacuum valve used on many cars but in a different form factor.

You might be able to take is apart though I'd expect the internal rubber parts to be baked from engine heat.

At $30 a pop + shipping x 6 you'd think there'd be a more definitive answer...

This governs flap positions of ac/heat system air flow. Has nothing to do with the engine - soot heat etc - it's located right next to the front passengers left leg behind the panel that separates the foot-well from the center column.

Yes, make sure it is actually bad by testing the coil / using a vac pump. If actually bad place an order for a new one and install. I'm all for fixing stuff / learning how things fail and I know this is the diesel list but sometimes just buying a new one is the most cost effective route.

It still sees interior heat, given your climate interior temps of 120 F are possible. Be aware that a small amount of oil fumes do make their way into the vacuum system as it bleeds down. In the 80's GM used a small carbon canister in the power brake vac line on gas cars to capture fuel fumes so they didn't attack the power brake parts.

Interesting. It looks like an updated switchover valve which regulates the ALDA on my 300SD. So it is something else.

Good to know.

Hmmm....it is very similar. I'm wondering if it's interchangeable. Especially, since the climate-control changeover valve is listed as NLA. Looks like another part to scrounge from the next salvage run.

It's appears to be sold here and elsewhere: https://www.pelicanparts.com/More_Info/0008000478.htm?pn=000-800-04-78-M22

So not quite NLA

Must not be the same as the switchover valve for my 300SD. Pelican wants $112 for a genuine Mercedes part and about half that for a knockoff.

If you are not concerned about originality there are many generic options. All you need to do is figure out the valve pattern: what port leads to what other port when solenoid is on / off.

For something like an intake flap / AIR pump diverter valve. What I'll call port A goes to a vacuum source , B goes to what you want to operate and C goes to atmosphere.

Assuming power to the solenoid = what you want to operate is on. Ports A and B are connected , port C is blocked.

No power to sol = item off. Port A is blocked , Ports B and C are connected ( this bleeds off vacuum at item B.

By the time you've found something that works and fits or have made it fit plus its price/shipping might as well have bought the stock item. Hence the question still stands: what goes wrong -wears out or breaks- inside the old valve and can it be fixed?

Vacuum Valve Repair
 

I've had very good luck using the Sam's Club degreaser to clean any of the various valves, set the sprayer on "STREAM" and fill it, let sit a day or two then rinse it out with tap water, good to go .

Nothing wrong with servicing a good used part ~ that's how actual Mechanics do things not just throw money at every problem .