another 190 owner with a question ;-)

Hey all.... I have a 91 1800cc UK Merc 190E... I have had the car for two years and one problem has been bugging me the whole time I've had it - the heater! The car doesn't have AC and the blower
appears to have only two settings - freezing cold or red hot - nothing in between... have asked around and one person mumbled something about a "duo-valve" that controls heat regulation. Can anyone confirm such a thing exists and maybe give some idea as to the location of it?! Also, there are two heat control dials on the dash....why two? Is it for front and rear control, or driver / passenger control? I'm guessing there is a fault with mine as either one I turn, makes all vents blow the same
Thanks in advance for any help! Regards, Dave
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The heater control valve is called the "monovalve" and can be rebuilt if necessary. Its default position is full heat. Follow the heater hoses from the motor to the monovalve.
Two temperature controls are for driver and passenger. One fan control is shared by both sides.
This heater should provide good comfort when its repaired.
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The heater control valve is behind the battery cover/firewall. You may have to remove the screen at the bottom of windshield to get full access. I may remember it wrong, but I thought W201 has mechanical valve, unlike the W126 which has electro-magnetic valve.
I know certain MB cars have dual-valve but I thought W201 has single. But again, my knowledge is limited to US model.
I just try to answer your question about the location. I have no idea what the real problem is. I assume your is manual control while all W201 in US have automatic climate control.
Dave Thompson wrote:

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Yes, the heater control valve (not duo-valve - this is in some other models) is located under air intake grille adjacent to blower.
It is vacuum controlled through the two temperature knobs, so it opens whenever one of the temperature control knobs are not in fully ccw position, or if there is no vacuum present due to a defect in the vacuum system.
The temperature is then adjusted by mixing hot and cold air through flaps mechanically linked from the temperature control knobs.
Your symptom indicates the heater control valve is working (heating is off when both controls are fully ccw and on when not), but probably air flaps are stuck in the hot position.
Check the linkage from the controls.
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Thanks to all for your thoughts and advice... guess what I'm going to be doing this weekend!! btw, whats the easiest way to get to the back of the heater controls...radio out? Thanks again, Dave
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