Sometime last week, I noticed that the heat stopped working in my wife's '95 E320 wagon. The odd thing (to me) is that the fan and a/c work fine. Defrost mode comes on fine too, but doesn't blow hot air.

Any ideas?

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Glen Tokuhara
Beauty & the Beast and the wagon that could!

Most likely the mono valve is stuck. unplug the mono valve and you should have full heat if not it is the mono valve or you are almost out of coolant.

Thanks, I'll try disconnecting the vacuum line to the mono and see if I get heat.

I unplugged the mono-valve solenoid and at first did not get any heat so I tapped on it with a small ball peen hammer. I then got heat out the vents!

So, I removed the solenoid and took it apart. The piston had some rust so I cleaned it up and put it all back together. It now moves smoothly but I don't think the system is working right yet.

It was a warm day (76F) here so I'm not sure if should get hot air out the vents or not but it felt like ambient air out the vents UNLESS I turned the temp wheel all the way to the detent. I tried a second pushbutton controller to make sure that wasn't the problem. I tried a second solenoid that I could plug in and watch. Unless the temp wheel was on the detent, the solenoid was engaged.

So...is there anything else besides the push button controller that signals the mono-valve solenoid? I will check tomorrow morning to see if I get heat but it sure seems like I'm not getting heat unless the the temp wheel is on the hot detent.

how many miles on the car? and how is the head gasket status? Mine was losing antifreeze while sitting overnight nosed down in my driveway. After driving a little the hot water start moving trough heater core and gave me heat
I was loosing about a 1/2 pint overnight and it was enough to get some air into the heater core.

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New Addition to the family
2013 Passat TDI 5Miles
2004 E500 4MATIC Wagon 95k
1996 E300 Diesel 173k Sold
1993 300E 2.8 230k Sold
1994 E320 White Wagon 373K Sold
Still dreaming about ....500E


Radu Negru

211,xxx miles. Head gasket changed at 128,000 about 5 years ago...no oil or coolant loss.

Just went for a drive and I do get heat but not as much as before. I'm wondering if the mono-valve itself may be part of the problem now.

Thats weird usually its the A/C that stops working first. At least thats the way its been for me.

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2015 ML350 4Matic. Wifes DD
2015 GLK350 4Matic. My winter DD
2012 E350 4Matic. Road Trip car
2009 CLK350 Coupe Designo.Kleemann Tune For nice days/DD
2006 CL600. V12.Eurocharged Tune. Enough said
2005 CLK55 AMG Coupe.Kleemann Tune. For the sound and style
2004 CLK320 Cabriolet. 2005+ Interior swap. For the sunny Florida days & beach days

could it be the gasket on the monvalve?

Well, it seems like it's working correctly now. This morning, it was only in the hi-50's so not very cold but the car heated up very nicely. I'll monitor it over the next couple weeks and see how it goes.

Also, I've been trying to source a new mono-valve solenoid. Fastlane doesn't have it...any leads?