[South16461]

So my problem is, my 1998 ML 320 heater works but only when I'm driving or have the RPMs over 1500... if i take my foot off the gas and let it go back down to idle rev then it starts blowing cold air again.... Anyone have any idea what this might be? AC and everything else work fine too so don't think its the AC/heater acuator or whatever, since it will blow hot air if I rev the egine or drive it etc. Any suggestions are more then welcome!
Thanks!
Kreg

 

[43sqd]

Read the below thread as it would seem that you have a partial blockage of coolant flow. Also check to see that the Coolant Circulation Pump is working.


http://www.benzworld.org/forums/w163-m-class/1549136-2002-ml500-will-not-generate-cabin.html

 

[Black3]

Not sure about the ML, but in some vehicles

that is a sign of low coolant level. Have you checked the level?

 

[Merzatt]

43sqd is spot on.

The primary source that circulates the coolant is main coolant pump. If you are not getting enough heat as you are used to or, it is taking too long for the cabin to warm up even though coolant temp is 80C, suspect this pump or blockage in one of the hoses.

Turn off the engine and open the hood. The auxiliary coolant pump should be running vibrant for 5 minutes after the engine turned off. Touch the hose and you will feel how much coolant is circulating via this pump. If you do not feel or hear it running, there is a DIY to replace it.