S500 hvac problem - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 07-24-2011, 06:09 PM Thread Starter
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S500 hvac problem

Hi, I am new to benzworld. I have a 2004 S500 4-matic with rear a/c (220.184). The symptoms are, when the a/c is on I have cold air coming from the front center vents only, and colder from the left center vent. In the rear I have cold air from the rear left vent and hot air from the rear right vent. A scan of the rear a/c controller gives me codes; B1426-A31/1m1 (circulation pump) and B1429-RR duo valve A31/1y2. I can not clear the Codes, they are hard codes. I suspect I have a problem in the front hvac and a different problem in the rear hvac. There is a duo valve in the Driverside rear engine compartment and a duo valve in the front right wheel well which I believe is for the rear hvac. I suspect I have a sticky rear duo valve on the right. Can anybody help me with the problem. Also, does anybody know if the front and rear duo valves are the same and interchangeable. Thanks in advance.

Last edited by Mrhooper; 07-24-2011 at 06:11 PM.
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post #2 of 3 (permalink) Old 07-24-2011, 06:34 PM
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Common problem for duovalves to stick. Inspect/clean them to see if that helps. After cleaning move them by hand to make sure they move freely.

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post #3 of 3 (permalink) Old 07-26-2011, 01:04 AM
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I think that you can initially progress this fault without dismantling components by checking the temperature (by hand) of the hoses in the front/rear duovalve systems. If cold, after a suitable warm up period, there might be a problem with the duovalves.

These drawings should help you get your bearings. As you know, the rear duovalves are behind the right front fender, so you will have to remove the wheel & the fender inner liner to get at it.
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