I'm starting to work on several issues my old '82 SEC has. Frist I'm looking into the climate control system. I have constant heat unless I roll the dial all the way up to get the AC to come on, and then it blows cold. I've checked the monovalve inside and all looks good; rubber is in fine shape with no cracks or deterioration, and the solenoid works the plunger. I did notice that the solenoid is active (plunger extended) no matter what setting the system is on. Is this correct? Are there any other rubber components within the monovalve body itself that I couldn't see?

My next stop in this diagnosis is resoldering/cleaning the control board. The blower works on high/low speeds, but not all the time in all switch settings. This seems like a needed thing to do on a 20+ year old car. What else can I look for if this doesn't take care of the problem?

Cliff

I think you should check the push button control board. I had the same problem on my first 420SEL that I had. Although I pressed the "off" button, I would still get air coming in. I didnt replace it becuase the unit is so darn expensive. I just sold the car and bought another benz. GL

An interesting point. Maybe we need a thread where members can fess up to why they really got rid of a benz.

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65 190d sold
85 380SE sold
87 560 SL 180K
84 380SE 96K (mint)

Yep, Two560Two, I'll be looking at the whole module real close.

My guess would be either the temp sensor that measures the air temp inside the evap housing or the cabin air temp sensor is bad IF it is not the pushbutton unit. Not sure where these sensors are on your car. Find them, disconnect them and see what kind of resistance you get accross them. If you don't get any then it is bad.

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Jim

Just this evening I took dash apart and removed the control box. It's got a date code of 2001 and a "www" address, so it's obviously been replaced. Thats not to say it could still have a problem, but I kind of doubt it. Since I can see behind dash now, I'll investigate some of the vacuum valves to see if they are working correctly. Maybe broken diaphrams in there.

I'll locate the evap sensor and test. I think the cabin sensor is in the roof panel by the dome light. There's a hole there I can stick the tip of my finger in, looks like a cover or something is missing. What would it look like, this sensor?