ultranank

Having replaced a damaged rear SAM module, and dried out wet carpets I went to check the reed valve in the front cowl for debris blocking any water drainage. There was a few leaves and twigs covering it, but not enough to cause the flooding to the rear SAM. A previous mechanic must have broken the valve in order to fix a water problem. I've checked MB forums over this known issue, and some suggest removing the valve completely, as well as adding a valve in the side of the cowl assembly to allow water drainage. My question is, is a reed valve over the air intake necessary, if so, are these valves available as a spare part seperately, or do I need to buy the whole cowl assembly? I notice there are two outlets the valve covers, presumably one for air intake to the filters and climate control, the other for water drainage? Advice would be much appreciated!

tusabes

The reed valve is completely unnecessary , it just is supposed to block debris while letting water pass
Jaguar had a similar problem with a rubber piece called a duckbill

In both cases they get clogged with debris then water accumulated rather than passing through , and overflows into the AC blowers then into the interior carpeting . Very stupid design and very simple to fix

You don't need to add any Valve anywhere - simply drill a hole in the lower side of the plastic reservoir where the water accumulates, so it can never pool again

wallyp

In both cases (Benz and Jaguar) the valve is there to stop leaking exhaust from entering the interior of the vehicle. Auto manufacturers are super-sensitive to that possibility ever since GM killed a family with CO back in the 1960's. The engineers consider it totally unacceptable to have an open pathway from the engine compartment to the interior.

I was amazed when posts appeared in the Forum saying that Benz suggested drilling a hole into the HVAC intake plenum from next to the exhaust manifold.

ultranank

Thanks or the input guys. Wally's point about blocking off CO from the air feed to the cabin is a valid one, and I have a solution to drain water from the cowl, routing it away from the exhaust. I'll keep you informed.

tusabes

The principle of keeping CO out of the cabin is not the purpose of the reed valve Wally , which is why Mercedes itself suggests drilling a drain hole in the reservoir

In actuality , in both cases of the Mercedes reed valve and the jaguar duckbill , the only purpose is to block debris while letting water to pass. They do not stop air /exhaust from passing anywhere , that is not their purpose . They are not airtight and exhaust can still pass through them even when unclogged

The reservoir with the reed valve is behind the first false firewall , so there is no issue with drilling a hole in the reservoir . You just need to make sure the location where you drill the hole doesn't dump water on the fuse box