Brrrr.... no heat in the cabin

Check to see if the small electric water pump is working. If it is then check to see if the solenoid mono valve opens to let water into heater core. Takes just a few minutes to remove the solenoid mono valve for bench testing with a 12V source. Can easily rebuild if rubber diaphragm is ruptured on the mono valve.

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The valve guts are a BMW/MBZ part that costs under $50 for the kit. It is powered closed, so if you unplug the connector, the heat should go full hot, if not time for a valve rebuild. You can plug a 12v injector noid light into the harness and watch it flash on/off as you change the desired temperature selection.

 

You probably could do it in situ but then you won't be able to bench test if the valve is slightly leaking or not after the rebuild. Regarding coolant mess after valve removal I'd imagine a couple of plastic plugs on the hoses will minimise that problem. Here is photo of valve on my 98 RHD car. Image Unavailable, Please Login

 

You don't have to remove the housing from the car to install the rebuild kit. Relieve the pressure in the cooling system by opening and then closing the radiator cap.
Sometimes it is easier to install the kit if you remove the two screws that hold the valve to the car. Pinch off the coolant hoses. Remove the four screws. Pull out the guts, install the new inner part with wavy spring. Be careful when reassembling to get orientation of everything as original. Don't pinch the main wires from the electrical connector to the large coil winding against the main top plate. Plug it in and you should be good to go.

 

This explains my issue. No heat inside the cabin and the water temperature is rising around 115c with both fans working in traffic!

Firstly I noticed someone has repaired the expansion bottle, so I replaced that and topped up with distilled water, however I feel the system still has air.

Now to tackle the heater valve. The part Bosch number Is 1147412013 and the same valve is fitted to a Rolls Royce.

If a whole new unit is required a similar valve 64111373188 fitted to various BMW models is available from the main dealer.

 

When either one of you had no heat did you try setting the heat to full hot and still did not get heat.

Today I had no heat when set to auto and the heat set to 72, even turning the heat up didn't work until I turned it all the way to full heat, then it would still heat on lower settings but I had to do the full heat every time after a shut down.

I'm wondering if the solenoid valve repair is what I need

 

Hi

Yes turned to full heat and still blows cold.

 

Just a heads up to anyone else needing to do this job; absolutely make sure to get the monovalve repair kit from Mercedes and do not use the aftermarket kit as it's total junk. The monovalve diaphragm commonly fails as age takes its toll and I've had enough (many years as an MB wrench) experience doing them on Mercs to know not to use the aftermarket kit.


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Wonder if this is another result of earlier owners not changing the coolant regularly because the WSM/maintenance schedule does not have regular change intervals specified.

 

I think so too. Mine has green coolant. Terry after reading your posts I ordered zerex g-05 from the USA as its not available here and will flush out system on my next service. Many thanks.

 

Bump for an old thread.

I did my monovalve repair this week and have restored very adequate heat to my car.

It seems both real Monovalves as well as Mercedes rebuild kits are quite scare now. The only real option was to use the Uroparts kit. Part number 0008350644R Its available everywhere and pretty simple for what it is. Like Asgor above, i found my diaphragm intact and still desecntly pliable, but with just a light smear of long term gunk on everything. Found a good rebuild video to follow on YouTube as well.

First tested wiring with my Noid light to assure power was getting to the switch.

Then unsecure collant tank and move aside. Its much easier than it looks.

Wiggle out the battery and you will have easy access to the monovalve. Not necessarily annoying, but no space wasted on this car. Like i have been told before on these cars, every easy job takes many steps to get to.

Two 10mm nuts and a tight fit with the cowl above secure the monovalve to the car. Once out remove the 4 flathead screws holding it on. I was unsure if any collant would flow out, have towels ready but fortunately none did. I didn't clamp either hose. Once apart, i used this video as a rebuild reference


Also made sure the flow restrictor at the bottom was free moving as well in its place. Reassembly was the opposite, just slowly securing the Flathead screws into the plastic housing. Once back to togther, I have heat at both idle and higher RPMs, in climate temp and Red dot settings.

I'm not sure if its my imagination as well as the cooler weather, but it also seems the car runs (displays) slightly cooler. If simply having all parts of the cooling system functioning in unison is just healthy for the total picture. Did about 160 miles the next day and even in traffic at 70* outside temps, temps barely went to the first mark to the right of the midpoint, but held there.

 

Well done, heat is good!

 

I was unaware that there was an electric pump down there until quite recently.
Awesome job and great information.

I read this and I think “Dammit, another thing that is just bound to fail on this car”. Almost everything is considered “consumable” like brake pads and clutches after 20k miles or 15 years. Fan motors (from heat), this thing, rubber parts in/around the gas tank, the guides for the door glass, the radiator itself, basically the fuse-board, throttle-cables, the belts, leather, you name it.

I saw a beat down 2007 Jeep Patriot on the streets in shambles but running like a champ. I grudgingly gave it all the respect in the world.

 

So true indeed. Dont forget about the other other electrical waterpump located in the bowels of the right front wheel well. Mine gave out on me earlier this summer and leaked coolant out in the driveway