2009 E350 weak heat - MBWorld.org Forums

Feb 11, 2022 | 09:03 AM

scotterikson

Thread Starter

Member

Joined: Apr 2019

Posts: 91

Likes: 16

From: Vermont, USA

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; Feb 12, 2022 at 04:47 PM.

Feb 12, 2022 | 11:39 PM

dvenneman

Member

Joined: Dec 2021

Posts: 192

Likes: 51

E350 4matic Wagon

2007 E350 heater control valve

Quote:

Originally Posted by scotterikson

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; Feb 12, 2022 at 11:40 PM. Reason: Misspelling