Heat blasting out of the front window defroster vents even when it is turned off
Thread Starter
Senior Member
Joined: Dec 2012
Posts: 445
Likes: 11
From: Washington, DC Metro Area
Currently: 2019 E450 AWD, Previous: 2002 CLK55 Cab
Heat blasting out of the front window defroster vents even when it is turned off
Apologies in advance to all. I posted this a few days ago in the CLK 55 specific forum and as I am still new I think that it would be better placed in this forum, which I just found. I hope that I am not violating rules by posting this here as well but after 67+ views and no responses I thought that I'd give it a shot.
Ok, I have had the car approx two weeks now and finally have the electronic version of the owners manual and I think that I have the heat and AC control settings down. That said the possibility of operator error can never be fully discounted. It is winter here and at start up I turn on the defroster. As indicated in the manual the defroster runs high and hard. I turn it off once the windshield clears. The good news is that the defroster is strong enough to heat the entire car so when I kill the defroster I leave everything off and the car keeps the heat for quite a while. HOWEVER, once I get onto the highway and am running at speed, the heat pours out of the defroster vents at the base of the windshield EVEN THOUGH I HAVE NOT TURNED THE DEFROSTER ON.
That is all controls are in the off position, no buttons lit and heat blasting me in the face like a hot desert wind at high noon.
I thought that it might be the REST, residual engine heat, function drawing heat off the engine but when I hit that button it does not light and otherwise does not seem to do anything. I get that this could be a symptom of the problem that I just do not know enough to recognize. I have the Star classic service manual library on CD for the car as I like to pull up schematics and blow up diagrams of each system as a way for me to learn and understand the vehicle. That said I have yet to find a the blow up diagram of the heating and AC system. Again could easily be operator error on my part.
What could this be? Bad thermostat? Some plugged up vaccum lines, stuck flaps in the HVAC system? I just took the car in for overdue B service and was feeling pretty good about things. The car drives nicely, looks and sounds great. This is the only real problem and it is in fact a problem as I just took a 400+ mile round trip road trip. The only way that I could regulate the temperature and keep it tolerable was to partially roll down the rear windows in the dead of winter. Needless to say the GF is in a constant complaining mode about this though she loves the car enough that she is currently going with the window roll down solution pending a better fix.
Any ideas? What am I doing wrong? I am sweltering in snow storms here! Thanks.
Ok, I have had the car approx two weeks now and finally have the electronic version of the owners manual and I think that I have the heat and AC control settings down. That said the possibility of operator error can never be fully discounted. It is winter here and at start up I turn on the defroster. As indicated in the manual the defroster runs high and hard. I turn it off once the windshield clears. The good news is that the defroster is strong enough to heat the entire car so when I kill the defroster I leave everything off and the car keeps the heat for quite a while. HOWEVER, once I get onto the highway and am running at speed, the heat pours out of the defroster vents at the base of the windshield EVEN THOUGH I HAVE NOT TURNED THE DEFROSTER ON.
That is all controls are in the off position, no buttons lit and heat blasting me in the face like a hot desert wind at high noon. I thought that it might be the REST, residual engine heat, function drawing heat off the engine but when I hit that button it does not light and otherwise does not seem to do anything. I get that this could be a symptom of the problem that I just do not know enough to recognize. I have the Star classic service manual library on CD for the car as I like to pull up schematics and blow up diagrams of each system as a way for me to learn and understand the vehicle. That said I have yet to find a the blow up diagram of the heating and AC system. Again could easily be operator error on my part.What could this be? Bad thermostat? Some plugged up vaccum lines, stuck flaps in the HVAC system? I just took the car in for overdue B service and was feeling pretty good about things. The car drives nicely, looks and sounds great. This is the only real problem and it is in fact a problem as I just took a 400+ mile round trip road trip. The only way that I could regulate the temperature and keep it tolerable was to partially roll down the rear windows in the dead of winter. Needless to say the GF is in a constant complaining mode about this though she loves the car enough that she is currently going with the window roll down solution pending a better fix.
Any ideas? What am I doing wrong? I am sweltering in snow storms here! Thanks.
Thread Starter
Senior Member
Joined: Dec 2012
Posts: 445
Likes: 11
From: Washington, DC Metro Area
Currently: 2019 E450 AWD, Previous: 2002 CLK55 Cab
I'll try it tonight. Best case if it works I can cancel my service appointment at the dealership for Friday. Thanks.
Thread Starter
Senior Member
Joined: Dec 2012
Posts: 445
Likes: 11
From: Washington, DC Metro Area
Currently: 2019 E450 AWD, Previous: 2002 CLK55 Cab
Attached: wireharnessdamage3.JPG (182.6 KB)*wireharnessdamage.jpg (64.2 KB)*wireharness2.jpg (41.7 KB)
The techs are will repair these two wires and are tracing out the
Rest of that section of the harness to make sure that the little buck toothed SOBs didn't go looking elsewhere for a chocolate,cherry or vanilla flavored wire! Credit to the service department for being thorough and for working with me to keep the cost of the repair down. Should be ready late this morning. Thanks again.
Newbie
Joined: Jul 2013
Posts: 1
Likes: 0
C300
the problem was blowing a/c air thru the front defroster----found i problem the there a vaccum line grey-green plastic piping on leftside firewal gots to the right into a connector was cracked, so i cut the conector out and connected it with a rubber vacucm hose over it and solved the problem
Last edited by ArvinPatel; Aug 30, 2013 at 01:45 PM. Reason: added info
Newbie
Joined: Feb 2016
Posts: 1
Likes: 0
Mercedes Benz ML 350
My ML 350 2003 is blowing heat from the front dash vents, the controls do not work, tried turning the controls to cold or 'OFF' do not change anything. Does anybody have any ideas what could be the problem?
