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:confused:Hi. I have a '98 Mercedes S320 and my climate control doesn't respond at all despite control panel lights up. I've checked both the front and back fuses and they are all working. It occurred to me that it could be the climate control relay, but I can't locate it. Can anyone please advise where I maybe able to find this and what it looks like? Many thanks, albert
 

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Hi Albert, just to confirm, is it that your, small red lights come on, but the blower (fan) doesnt start up, or nothing happens at all, if its no blower (fan) then it is most likely your relay on top of your blower housing, there are lots of info on this problem already explore the posts.
Cheers EJ
 

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Thanks EJ, yes, the small red lights and all the LCD come on. I can even press various buttons to turn on different red lights, and can change the temperature settings, but no fan at all and the compressor doesn't seem to come on. Does this sound like the relay? To get to the relay, what parts do I need to take off - the long moulding just under the wipers and in front of the firewall? Please advise.

Thanks,
Albert.
 

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Albert, the first thing you should do is pull the fault codes from your A/C system. Why take guesses when the car will tell you exactly what the problem is! :)

The procedure to pull sensor data and fault codes is here (don't eorry about it being for an E-Class, the procedure is the same):

How to Diagnose Air Conditioning Malfunctions | EclassBenz.com

Let us know what you find.
 

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Hi Bob or yone else who can help,
I've now got the numbers - it's a great tool. I've now got to work out what to do. My sensor #2 (outside temp) reads well too high (111F, and it's going into winter here in Oz; my estimate should be around 50F). I entered the various numbers into the tool recommended by Bob, and got the following diagnostics:
B1227: sensor 2 reporting implausible temp.
B1416: collant circulation pump powers the 'REST' residual engine heat function and may be involved in circulating coolant after the engine shuts off to help with engine cooling.
B1417: left side of duovalve is malfunctioning.
B1418: right side of duovalve is malfunctioning.

I also have the E FF code which was not explained by the tool.

So, I'm not sure what to do now.

Can anyone advise where is the outside temp sensor (#2)?
Where are the duovalves located and what do they look like?

Could a faulty climate control/regulator cause the above?

Thanks,
Albert
 

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E FF means you have reached the end of the fault code list.

Re: the regulator. Here's a good write-up over at peachparts.com on how to diagnose/repair it:

PeachPartsWiki: Diagnosing the Blower Motor and Cabin Filter


Basically the regulator works by varying the ground potential to the motor. If you look at the two wires going to the blower motor, the red one is +12v and is hot all the time (even with the key off!). The blue wire is controlled through the regulator. To test it, simply jumper the blue wire/terminal on the motor to a ground point. If the motor is good it will start running at full speed and you know you have a bad regulator.

Anyway, read the article and it will explain all.

Duovalves are relatively easy to repair as well. Here's an article on doing it for the rear AC. The duovalve is in a different location, but the procedure is the same:

V12 Uber Alles, Rear AC System and Duovalve Diagnosis Rebuild in a W140 Mercedes Benz
 
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