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  #1  
Old 11-22-2014, 08:26 PM
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Location: Red Boiling Springs Tennessee
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Dash out - now testing switch over valves

For two years my 190d has been blowing hot air only, and the flaps do not work. I tried a new CCU, but it did not solve my problem. Today I removed the dash to try and find a vacuum leak. I tested vacuum going into the switch over valves unit. The green/brown line comming from the vacuum pump I tested the unit for vacuum and it holds. The red line from the heat control valve it holds vacuum. When I tested the five white plastic hook ups none of them held vacuum. When I took off the lines from the unit and tested them they all held vacuum. Since all the lines after detached from the unit hold vacuum it looks like I don't have a problem there. Also, I noticed that when vacuuum was applied the flaps did move. I'm wondering if the white plastic lines comming out of the unit should hold vacuum. Thanks for your help.

Hugh,, Sr.

1984 190d (W201) 132.432
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  #2  
Old 11-22-2014, 11:19 PM
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Location: Redding, California
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Look at the potentiometer. When I had similar problem with mine I checked everything, swapped the CCU. Turned out that's what it was. Changed that out, adjusted it, and the AC has been working as it should for a couple of years now.

Troubleshooting the Mercedes-Benz 190 Tempmatic ACC Climate Control System
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  #3  
Old 11-23-2014, 05:25 PM
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What is a potentionmeter, and where is it located?

Hugh Sr.
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  #4  
Old 11-24-2014, 10:48 AM
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It's located at the top of the heater box. The only white thing up there. Pictures of it in the link included in previous post. Those instructions also show the means to test and adjust.
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  #5  
Old 11-25-2014, 10:01 AM
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I read the article on testing the potentionmeter. It says that the wheel on the CCU needs to be turned to the MIN position. Before I took out the dash I replaced the CCU with a new one, and the problem remained. So, will it do any good to try and test the potentionmeter when it probable does'nt receive any signal from the CCU? Also, when testing the switch over valves for vacuum. The article says that you need to crank up the car to test for vacuum comming out of the switch over valves. With the dash out and all those wires laying around I'm a little bit hessitant about sending any electricity through the wires. I was wondering if I could use my Rainbow vacuum cleaner to provide vacuum to do the test? I tried a shop vacuum cleaner, but it only provided about 5 (can't remember the letters that go beside this number). I appreciate your help. Happy Thanksgiving.

Hugh Sr.
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  #6  
Old 11-25-2014, 02:49 PM
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Quote:
Originally Posted by hsmith View Post
I read the article on testing the potentionmeter. It says that the wheel on the CCU needs to be turned to the MIN position. Before I took out the dash I replaced the CCU with a new one, and the problem remained. So, will it do any good to try and test the potentionmeter when it probable does'nt receive any signal from the CCU?
You're reaching inaccurate conclusions. Yes, will will do good.

Quote:
Originally Posted by hsmith View Post
Also, when testing the switch over valves for vacuum. The article says that you need to crank up the car to test for vacuum comming out of the switch over valves. With the dash out and all those wires laying around I'm a little bit hessitant about sending any electricity through the wires.
Those wires are disconnected and ends are insulated. Not other way to do it. It's not a problem. Use a MityVac for testing the pods, or use the vacuum from the running engine.
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  #7  
Old 11-25-2014, 03:23 PM
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I woiuld't doubt that - reminds me when I use to jump out of helicopters - I always felt releived when the chute opened. I'm just wondering how in the world to test it if changing the CCU didn't have any effect on anything. If I turn the CCU wheel down to MIN (that's what it said in the article) would it go ahead and send signals to the p-meter eventhough the flaps still don't work? Thank you

Hugh Sr.
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  #8  
Old 11-25-2014, 07:24 PM
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Yes.

New CCU you'd have to assume it's not defective.
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  #9  
Old 11-30-2014, 11:45 AM
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I found the vacuum problem. When I first started I tested the vacuum between the vacuum pump and the yellow part just before the firewall. I got good vacuum. After I got the dash out and tested all possible vacuum connections, and got good results I was really down and out about it. So I went back to the line comming from the vacuum pump and bypassed the yellow part to the brown/green line. When I cranked her up all the system worked. I took the yellow part out and ran the vacuum through it and all the system still worked. When I ran the vacuum through the Y connector I did not get any vacuum. Some how the Y connector obstructed the vacuum. About the potentiometer. While the car is running I moved the wheel on the CCU and the temp was adjusted to where I put the wheel. I noticed that the p-meter arm moved according to where the wheel was set. It looks like to me that the p-meter adjusts the cold/hot air going to the system. If I can see that the p-meter is working would it be necessary to test the wire mentioned in the article for 4.5 volts? Thanks for your help.

Hugh Sr.
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  #10  
Old 11-30-2014, 12:08 PM
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I do not have manuals for your car... so I am just throwing out some stuff.....
that Y connector might have one way valve... check it in several directions...
since a potentiometer is a Variable Resister you need to test its ability to VARY the electricity going from it... by moving it and seeing the reading move on your VOM...
a Rainbow vacuum might suck your entire pod flap clean out of your car... use the mityvac as mentioned...
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  #11  
Old 11-30-2014, 01:38 PM
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One last thing before I put this back together. All the vents work properly according to the button pushed on the CCU. But, it sure does seem like more air comes out of the windshield vent than the floor vent. Is this the way it's suppose to be?

Hugh Sr.
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  #12  
Old 11-30-2014, 03:08 PM
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Location: Lake Norman North Carolina
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Do check all the actuator functions by cycling through the four punch buttons. If you have had a vac leak for sometime the actuators and linkages can be sticky even if they hold vacuum.
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  #13  
Old 11-30-2014, 05:51 PM
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Quote:
Originally Posted by hsmith View Post
One last thing before I put this back together. All the vents work properly according to the button pushed on the CCU. But, it sure does seem like more air comes out of the windshield vent than the floor vent. Is this the way it's suppose to be?

Hugh Sr.
That's the way mine works.
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