Hi Guy's - I have a 00' ML320 - and I cannot get the heater to work. The fuses are fine, the relay is working ( already had replaced with new one by dealer ), the water is hot, the blower motor operates. When I select the heater via the temp **** and set the vents to foot and windshield, and turn on the blower, it blows ambient temp air. When the temp **** is changed to cool and vents set for dash it blows super cold air. Problem is the mornings have the windshield iced and the interior cold, and I cannot get the heater/windshield defroster to operate - Blow hot air. Anyone with help it's appreciated. It's my only vehicle and I can't afford to have it spend a day or two at the dealer awaiting inspection. Thanks

 

THERE IS A AUX. WATER PUMP THAT SUPPLIES WATER TO THE HEATER CORE. IT IS RIGHT NEXT TO THE BATTERY. THIS FEEDS A GOOD SUPPLY OF WATER TO THE HEATER CORE TO HELP HEAT UP CAR FASTER ON COLD MOURNINGS. YOU SHOULD BEABLE FEEL THE PUMP WORKING WHEN THE CAR IS STARTED FIRST THING IN THE MOURNING, WITH THE HEATER ON.BEST OF LUCK.