On Oct 31, 2012, at 1:33 PM, "Jon Agne" <jonag...@gwi.net> wrote:
> Lately I've been having an issue about getting heat while the car is at any > sort of speed Here is a reply from Philip on the same question from my email archive. > Michael Canfield wrote: > The heater in my 83 300d only blows hot air when sitting > still at an idle. As soon as I start driving I can feel the > air start to cool off no matter how high the temp is set. That is the classic symptoms of the monovalve diaphragm leaking. The insert is replaceable and usually that's all that's needed. The monovale is a solenoid-operated flow valve and is located on the firewall, about centered, and has a heater hose in and out plus an electrical connection on top. In use, the solenoid moves the diaphragm as a flow valve. At full heat (no power) the spring is supposed to hold the valve open. At less than full power, the valve is feed a pulse width modulated drive voltage to turn on and off the flow rapidly so the average is somewhere between full heat and no heat. When the diaphragm gets a leak the water gets behind the diaphragm and at higher engine speeds the water force is more than the spring tension - so it is "turned off". At idle, the pressure is less, so the spring can turn it on again. Seems I don't have the part number in my notes. I guess the last time I bought one was before my note-file. But odds are good a new insert will set you right. -- Philip Rick Sent from my iPhone _______________________________________ http://www.okiebenz.com For new and used parts go to www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://mail.okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
