heater system 420sel

[just-n-time]

Hi gang as in the title I am having some issues with the heating system in our 420 SEL.
First it is putting out heat, but it will not blow hot as you travel down the road.
When you stop and shop then get back in the car it will blow hot for a short time then cool off.

I am thinking in terms of a vacuum problem with the fresh air vent.
I took the center console apart and found two vacuum pods, one rectangular, one round, and they both react when you change heat settings on the temp wheel.
I need the diagrams to tell me where the other four lines that come off the regulator valve go.
I have four lines that go up toward the top of the dash, they must go back out to the under hood area.

Thanks for any help provided, JNT

[whunter]

What you describe is a failed mono valve diaphragm, not a vacuum issue.

Fastlane: Mono Valve Repair Kit - Heater Valve
http://catalog.peachparts.com/item.wws?sku=W0133-1618202





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[just-n-time]

and the mono valve is the large black rectangular part under the console?

[Two560Two]

you can buy a repair kit and i believe it is located somewhere right behind the vehicle battery

[whunter]

Mono valve links thread
http://www.peachparts.com/shopforum/diesel-discussion/281902-mono-valve-links-thread.html#post2514617


Damaged mono valve pictures please
Damaged mono valve pictures please

[DAVECAD2.0]

Originally Posted by just-n-time

Hi gang as in the title I am having some issues with the heating system in our 420 SEL.
First it is putting out heat, but it will not blow hot as you travel down the road.
When you stop and shop then get back in the car it will blow hot for a short time then cool off.

I am thinking in terms of a vacuum problem with the fresh air vent.
I took the center console apart and found two vacuum pods, one rectangular, one round, and they both react when you change heat settings on the temp wheel.
I need the diagrams to tell me where the other four lines that come off the regulator valve go.
I have four lines that go up toward the top of the dash, they must go back out to the under hood area.



Thanks for any help provided, JNT

The other vac lines off the shuttle valve (the long black vertical thing with all the vac lines) go to 4 other vac pods under the dash not back out. Two pods that work in tandem (push/pull) located behind the glove box or on my '91 the air bag. One next to the gas pedal. And one above and forward of the round one you saw. The remaining 4 are all round.
Look next to the fuse box. You will see two vac lines attached to a round yellow/gray thingy on the false firewall. It's a one into two vac spliter and check valve. As I recall the two lines from it are the only vac lines that go into the car. The red w/white stripe vac line goes to, and is the feed (suction source) to the shuttle valve. The other line gray w/white stripe goes to something (can't remember) above the gas pedal.

[just-n-time]

Thank you for all the great posts and pictures, just one more question, I do get air flow threw the vents with the system off, on our 91 190E it was a vacuum pod that controled the fresh air vent. dose this make any difference in the scenario?