In my 1999 ml430 when I turn on heat it blows cold air what can I do on 1999 Mercedes-Benz ML430

I changed cabin filter still blows cold air what's next

by in Brooklyn, NY on December 09, 2013
2 answers 3 comments
ANSWER by , December 09, 2013
Replace the thermostat, it is probably stuck in the closed position.
COMMENT by , December 09, 2013
Where is thermostat
ANSWER by , December 09, 2013
could be blend door stuck open
COMMENT by , December 09, 2013
What is a blend door???
COMMENT by , December 09, 2013
It's a door inside the HVAC housing that controls the airflow through the heater core and A/C evaporator , to regulate air temp. Cabin filter - filters air. Stuck closed thermostat would cause overheating. CHECK coolant level first , and make sure the engine is reaching proper operating temp.