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  #1  
Old 04-30-2013, 09:33 PM
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190DT Heater Valve

Until I can get my climate control operating properly (if ever), I would like to manually prevent coolant from entering the heater core. On my 87 190DT, I have been able to engage the A/C compressor when I press the defrost button. However, it's hard to get the car cold because I still have hot coolant coming through the heater core.

Everyone points to the heater valve, which on my car is behind the battery (passenger side) under the leaf catcher between the two firewalls. I have replaced this valve with a new valve. I have diverted the entire climate control vacuum to this one line (a dark red vacuum line). I have manually clamped the hose. I have held the valve closed, then inserted a plugged piece of hose over the vacuum nipple to keep it closed no matter what. None of these things have prevented hot air from coming out the defrost, and hot air from coming out the side vents. The glove box is piping hot as well as the metal pipe running through it.

I searched the service manuals for a diagram of coolant flow through the core. I found one diagram that barely shows it (attached). It appears that the coolant ENTERS the heater core on the DRIVER'S side and exits on the passenger side. If this is true, my valve/clamp is blocking the exit of hot coolant, not the entrance.

So either the diagram is wrong, I can't read the diagram properly, the location of the valve is wrong or I'm a complete idiot and don't understand how to keep out the heat. What gives?

It seems to me the answer would be to clamp the hose where the #6 is pointing. Any ideas?



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87 2.5L 190D Turbo 5-speed - 102k (Daily Driver)
82 300D Turbo - 145k - Light Ivory (near mint)

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  #2  
Old 04-30-2013, 09:49 PM
1985 190d
 
Join Date: Nov 2006
Location: canadian border vermont
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Troubleshooting the Mercedes-Benz 190 Tempmatic ACC Climate Control System


Google the line above for a good writeup of the w201 system
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  #3  
Old 05-01-2013, 12:00 AM
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Thanks for the input. I found the link below which provides some helpful tips for getting the entire ACC to function as designed, but it doesn't answer my question about manual heater / air conditioning.

Troubleshooting the Mercedes-Benz 190 Tempmatic ACC Climate Control System
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87 2.5L 190D Turbo 5-speed - 102k (Daily Driver)
82 300D Turbo - 145k - Light Ivory (near mint)

Gone: 85 300D Federal - mileage unknown
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  #4  
Old 05-01-2013, 08:05 AM
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Location: Ooltewah, TN
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Living in Florida, you don't need the fuel heat exchanger IMHO. If I were experiencing your problem and clamping off of the heater hose didn't stop the flow of heat, I would get several feet of heater hose and bypass the entire heater system (4,5,6,7) for the summer months. I'd throw 5 away and put a plug in 4 and 6 for the summer to keep any trash out of the heater system.
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Old 05-01-2013, 10:44 AM
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Maybe a better solution would be to install two bypass valves, one at 4 and one just before 5. Then I wouldn't have to plug and remove the lines, just simply turn the valve.
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87 2.5L 190D Turbo 5-speed - 102k (Daily Driver)
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  #6  
Old 05-01-2013, 02:16 PM
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Common plumbing shut off valves should work if there is space in there to install. If you plan to fix the system it would be a lot less trouble to just get the heater hose.
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Old 05-21-2013, 06:23 PM
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Just to update anyone following this thread, I was finally able to shut off the heat. It appears the clamps/valve I used were ineffective at cutting off the flow of coolant. A pair of harbor freight vice-grip hose clamps did the job. Clamped the hose behind the valve cover on the passenger side, just downstream of the heater valve. No more heat coming out of the defrost or side vents.

Tip to anyone with W201 AC issues. In both cars I was able to actuate full AC blowing out all vents on the highest fan speed (not adjustable) by pressing the defrost button on the control panel. Seems if most controls crap the bed, that one remains. Now my cabin is nice and cool in the FL heat.
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87 2.5L 190D Turbo 5-speed - 102k (Daily Driver)
82 300D Turbo - 145k - Light Ivory (near mint)

Gone: 85 300D Federal - mileage unknown
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  #8  
Old 05-22-2013, 02:15 PM
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The defroster is functioning correctly!

When the far left defroster button is selected, you get max full fan, FULL HEAT and AC it's designed that way for rapid defrost/defog.


I'm really stuck with the vacuum discussion and the monovalve. It's electric.

It's normally open (unpowered) and held closed (powered) The monovalve core can be purchased for $15.

This is one of the most common issues with 107/201/124/126 as the car ages. Whatever you changed that had vacuum lines running to it was NOT the mono valve, the main control of water flow through the heater core. It should have had electrical power to it, not vacuum.
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  #9  
Old 05-22-2013, 11:20 PM
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I changed the heater valve, not the monovalve. The heater valve is vacuum as listed in the FSM. I am familiar with the monovalve on W123 but don't know if I've seen one on the W201. Not saying it isn't there though.

My problem was CONTINUOUS heat, no matter what selection, from both side vents and defroster vents. Also the push buttons would not engage the blower motor, except on defrost. The jerry-rig fix was to block the coolant flow and push the defrost button to engage AC with blower on HIGH.

Eventually I would like to get the CCU to function properly, but now I'm content with my half-fix.

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82 300D Turbo - 145k - Light Ivory (near mint)

Gone: 85 300D Federal - mileage unknown
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