WikiTim

Hello everyone!
Hope you all are staying warm this winter because I am not.
I drive a 2000 ML320. I am currently having a very weird problem with it that no one can give me a proper answer to. Instead of speading all my money replacing one part at a time, Ill post about it again...
My ML does not produce heat when the outside temp is below 45 degrees F. The temperature of the air outside.....
Its very odd. It doesnt make any sense to me or anyone I've talked to. The vehicle does no overheat and it gets up to normal operating temp (80c) at a normal time so obviously nothing is wrong with the thermostat or engine cooling. The door flap actuator does need to be replaced but i have it pushed over to heat manually so that is also not the issue. Ill actually replace the actuator this spring. otherwise I am lost on this one. It blows my mind that it will not produce heat under 45f even after the car gets up to temp.
any ideas?

Maj. Dundee

Check your Outside Temp. Sensor and see if it is dislodged from its' holder, check wiring.

WikiTim

My outside temp sensor works accurately. However i dont understand why the outside temp sensor would cause a problem with the car making heat??? Please explain.

Maj. Dundee

Although the sensor is for the A/C, I thought it could be a possibility.

Is your coolant circulation pump working with the key on?

WikiTim

yes. replaced it in nov. works fine

WikiTim

any other thoughts or ideas? it was exceptionally cold this morning >_<

Maj. Dundee

Tim, I have no further suggestions. Never heard of this problem.

Maj. Dundee

I emailed a friend of mine who works for M/B and this was his response to your problem.

Typically poor circulation through the heater core.

First thing to check is temp at heater core outlet. With blower off it should be close to engine operating temperature.

By the way, are you using golden or green coolant?

Maj. Dundee

Here are a couple of threads on the same issues. Follow Witek's info who I got in touch with, he's the best.

https://www.benzworld.org/threads/no-heat.3008311/

https://www.benzworld.org/threads/20.../#post-4394160

hyperion667

You live in Texas by any chance?