A failed digital heater control valve can cause a lack of heat output from the climate control system.Google+
Car Problem Reports
Mercedes-Benz E500 Failed Digital Heater Control Valve May Cause Poor Heat Output
Mercedes-Benz E500 Problem
Average Mileage: 99,587 mi (74,250 mi - 140,000 mi)
I have the same problem no heat or no ac and next day everything works fine. I googled the problem and I found that it was a common problem with e500 2003 to 2005 Now I have ac working but blowing hot air in the back vents. So just purchased a new HEATER CONTROL VALVE (PART# A 211 832 05 84 )for $45.00 on ebay and will be installing at the end of the week. That will take care of the problem Note this is the updated valve by mercedes to replace the original part The difference with the original # and the new is the 5 instead of the 6
Visitor, 2005 Mercedes-Benz E500, 78,000 mi
1st cold day put on my heater and NO HEAT !Took it to CHANDLER MB they say I have a bad Heater Control Valve, NOT COVERED under my warranty ! So I am looking at $ 498.00 Installed by the Dealer, they say it's a lot of Labor to put in !
David Mesa, AZ
Visitor, 2003 Mercedes-Benz E500, 74,250 mi
Blower works fine but the heat is not coming on at all. When the engine is warm, it maintains around 190 deg F like it should so it is not the engine thermostat.
Visitor, 2005 Mercedes-Benz E500, 80,000 mi
No heat. Also back seat air is blaring heat on hot days/long drives with back seat controls off and on "low" as possible temp!
Visitor, 2003 Mercedes-Benz E500, 79,000 mi
Heat quit working in front and back of car
Visitor, 2003 Mercedes-Benz E500, 130,000 mi
Once the engine warms up when I turn on the heater it will blow warm for 5 seconds and then blows cold. Not overheating.
Visitor, 2005 Mercedes-Benz E500
no heat blowers blowing cold air when heat is on (not fixed)
Visitor, 2004 Mercedes-Benz E500, 140,000 mi
Only cold air. no heat.
Not sure how long I have had this problem..no one rides in the passenger seat. The heat on the driver side works perfectly fine, however, the heat on the passenger side is blowing cold air only.
Visitor, 2003 Mercedes-Benz E500, 108,000 mi
cold here and not heat