Your heater will blow cold air only.
The a/c - heater controller is out...........
if the heater does not blow out warm air change the setting.
Low on coolant. Stuck open thermostat. Plugged heater core. Faulty temp blend door.
Low on coolant. Bad thermostat. Plugged heater core. Temp blend door inop.
you may not have the heater water hoses plugged in
The heater does not blow air because it emits infrared rays that have heat molecules within them, thus releasing heat, not blowing it. A heater does not blow air becasue there is no moving air source within the heater. The heater emits infrered rays that cause heat to slowly flow out of the heater.
Assuming you want it to blow hot air, you may be low on coolant or have a stuck open thermostat or a plugged heater core or you have a faulty temperature blend door actuator.
The heater core is blocked, or a heater hose has collapsed, keeping hot engine coolant from getting to the core. The "blend air" door may be stuck in the open position, keeping warm air from circulating, and dumping in cold outside air. I am assuming that engine coolant and water pump is good.
replace front heater corefront and rear have independent heater cores
You are low on coolant to the heater core.
You need to back flush the heater core have had to do it to my jimmy 2 times and fixed the problem is easy fix .