Could be,
low on coolant,
stuck open thermostat,
plugged heater core,
faulty temp blend door actuator,
the blown head gasket would make it over heat. but it wouldn't cause the heater to blow cold, it should actually blow hot if that is wat happened
heat core. leak. thermostat. no antifreeze.
It doesn't really blow it out it just warms the cold air.
Cause its broke!
alve, check vacum line first (on heater valve)
No, not if it's on a heat setting. Most home thermostats have a "Fan" setting that will blow cold air if the attic is cold.
heater core possibly plugged and leaking
No! Thermostat.
Check Antifreeze level..make sure there are no leaks under the vehicle.
The heater bypass valve is not fully closing, or leaking hot coolant into the heat exchanger.
The front expansion valve is clogged.
Thermostat and/or heater core may be defective