E-Class (W211) 2003-2009

2009 E350 weak heat

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Old 02-11-2022, 09:03 AM
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01 clk430, 05 e500 4matic
2009 E350 weak heat, not the usual suspects

Car has very weak heat. Heat trickles out if I run the fan on a low speed, cools quickly if I set to "auto" or turn the fan up higher. Had a code for the heater valve, replaced with genuine from FCP. Figured I had a bad L/F SAM, replaced with a used one from a reputable Ebay seller (Garageman Inc), no change. I have a DAS3, checked ACC functions, no errors reported. Replaced electric circulation pump (even though I could hear original working), no change. Car otherwise functions properly, temp comes up to normal as it should, A/C charged and working

Clogged heater core? (seems unlikely) Broken blend door flap? Suggestions/experiences welcome

Last edited by scotterikson; 02-12-2022 at 04:47 PM.
Old 02-12-2022, 11:39 PM
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E350 4matic Wagon
2007 E350 heater control valve

Originally Posted by scotterikson
Car has very weak heat. Heat trickles out if I run the fan on a low speed, cools quickly if I set to "auto" or turn the fan up higher. Had a code for the heater valve, replaced with genuine from FCP. Figured I had a bad L/F SAM, replaced with a used one from a reputable Ebay seller (Garageman Inc), no change. I have a DAS3, checked ACC functions, no errors reported. Replaced electric circulation pump (even though I could hear original working), no change. Car otherwise functions properly, temp comes up to normal as it should, A/C charged and working

Clogged heater core? (seems unlikely) Broken blend door flap? Suggestions/experiences welcome
I think this problem is more likely to be the heater control valve. I have an 07 with 244k and I replaced the thermostat a few months ago with a “no heat” problem and all was well. Just had a mixed cold air at dash vents and weak hot air at feet - its winter here in the US. This seems to be a valve issue. The heater control valve apparently operates about 8 or so smaller HVAC motors. I’m going to replace mine. I don’t think there is any reason right now to suspect a heater core or a “blockage” for you. Valves are wear out parts. Best and good luck.

Last edited by dvenneman; 02-12-2022 at 11:40 PM. Reason: Misspelling
Old 02-16-2022, 06:47 AM
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01 clk430, 05 e500 4matic
Brand hew, genuine valve installed before post

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