Why would a car heater stop working and just blow cold air?

Answer 1

There are several reasons for your heater to blow cold air, the heater belnd door being stuck, no thermostat, low coolant, diagnosis is key.

If you have a 3.1 V6, you may need to bleed the coolant system. In front of the engine passenger side, you have a bleeder screw, with the engine off, surge tank cap off, open the valve until coolant flows smoothly, close the valve, check coolant, add if needed.

it's a $5.00 thermastat The problem could also be low coolant level. If the coolant gets too low it will not pass through the heater core and therefore will not heat the cabin air.

You may need to have your heater box inspected. It is possible for the flapper to be jammed or broken. It is a big fix so make sure to check coolant levels and leaks as well.

Answer 2