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  #1  
Old 07-02-2007, 09:04 PM
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1984 300D wagon Climate control questions

I am working on a 1984 300D wagon. When the A/C or Economy is turned on you get heat. It doesn't matter where the temp dial is....you get heat.
1) I rebuilt the mono valve as the old valve didn't work.
2) I checked the mono valve windings and they are good. I put 12volts on it after putting the new mono insert in and it moved it.
3) The A/C is running, Compressor engages and the low side line gets cold but still heat at the vents.
4) I replaced the push botton assembly with a known good unit and still hot air.
5) I checked voltage at the mono valve plug and it seems to vary between 2 to 8 volts???
6) I ran straight to the mono valve with 12 volts and the air got cooler.

Any good climate control techs out there??? This one is stumping me.

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.
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  #2  
Old 07-02-2007, 10:47 PM
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Could it be the interior temperature sensor ? The push button unit thinks it is too cold inside the car and tries to open the mono valve. I think the interior temp, atleast on my 87, 260E, is a negative changing resistor with increase in temp. Use a hair dryer and see if the resistance of the sensor terminal drops.
Otherwise, has to be the control unit if you know that approx 12V closes the monovalve completely.
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  #3  
Old 07-03-2007, 12:34 PM
david s poole
 
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if you set temp to max cool[wheel to detent position] will the air stay cool without any heat?
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Old 07-03-2007, 01:08 PM
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Quote:
Originally Posted by david s poole View Post
if you set temp to max cool[wheel to detent position] will the air stay cool without any heat?
No. It will still blow hot. When I set the temp to hot, it gets hotter. I can then see that the A/C is working some. The A/C does need to be topped off so it will work better but the heat definately overpowers any cooling effect.
WHERE is the other temp control box located?
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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.
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  #5  
Old 07-03-2007, 02:06 PM
david s poole
 
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under the glovebox you will see two boxes one is for temp[german name on it] and the other for fan speeds.they are both prone to go bad.the power for the monovalve [which should be 12vdc when calling for cooling] i believe comes out of the temp regulation box.
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David S Poole
European Performance
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4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
http://www.w108.org/gallery/albums/A...1159.thumb.jpg
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Old 07-03-2007, 04:39 PM
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Thanks David... I have a donor '83 and I will try the box from it. Thanks to you and others on this site, we can keep these neat cars running and COOLING. Chris
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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.
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Old 07-03-2007, 11:42 PM
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Just for info, the monovalve is operated about every 5 seconds. when the climate control calls for heat, the duty cycle is to turn the +12 off sooner. When the climate control calls for cooling, the +12v is applied longer. If you put the end of a screwdriver on the monovalve you should be able to hear it click about every 5 seconds or so. The monovalve has a primary valve, which is the solenoid slug, and a secondary valve, which is the diaghram. The diaghram needs the assistance of the pressure from the auxiliary water pump to push the diaghram closed. If the car produces heat at idle in hot weather, the auxiliary water pump is most likely inoperable.
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  #8  
Old 07-04-2007, 01:01 PM
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Quote:
Originally Posted by Richard Wooldridge View Post
Just for info, the monovalve is operated about every 5 seconds. when the climate control calls for heat, the duty cycle is to turn the +12 off sooner. When the climate control calls for cooling, the +12v is applied longer. If you put the end of a screwdriver on the monovalve you should be able to hear it click about every 5 seconds or so. The monovalve has a primary valve, which is the solenoid slug, and a secondary valve, which is the diaghram. The diaghram needs the assistance of the pressure from the auxiliary water pump to push the diaghram closed. If the car produces heat at idle in hot weather, the auxiliary water pump is most likely inoperable.
Richard... Thanks for the info. Are you saying that the Aux water pump runs full time or just at low speeds even with A/C on?
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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.
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  #9  
Old 07-12-2007, 12:41 PM
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I fixed the Climate control by changing out the TEMPREATURE controller box behind the glove box. Thanks David! I have also improved the A/C performance by rebuilding the MONO valve as they can leak some hot water while the A/C is on.
Thanks David AND Richard.

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.
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