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
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