Low on coolant.
Stuck open thermostat.
Poor circulation (plugged heater core).
you need to replace your heater core
Low coolant, failed thermostat, partially plugged heater core...............
Only blows cold air with the a/c on while driving, your cooling fan or fan clutch is bad depending on the year, make and model.......... Only blows cold air with the heater on while driving, you will have a bad or broken internal a/c - heater control door.....
Poor circulation probably due to a restricted (plugged up) heater core.
It is either your water pump or your thermostat
cool hello
Leak in heater core. Replace core.
The front expansion valve is clogged.
not developing enough vacuum while driving to keep the blend door open check your vacuum lines for leaks
heater core possibly plugged and leaking
thermostat probably damaged or stuck....and worse case scenario....your heater core is going out.
It doesn't really blow it out it just warms the cold air.