The heater blows great, but cold air, no leak in the floor, new thermostat. on 2000 Mercury Sable

No overheating, no leak in coolant. A/C works great. I was told to clean my vents, but how?

Asked by for the 2000 Mercury Sable
The heating and ventilation draws its air from the area at the bottom of the windscreen/wiper panel area, make sure leaves and debris are cleared from this area. I have had to remove the fan blower motor on several cars and remove a "nest" created by rodents in the heater ducts. Not sure if your car has a cabin air filter if so probably located behind the glove box, perhaps its restricted.