usually you will get antifreeze smell and steam inside coming from defrost
The most common signs of a bad heater core are; no heat or fluid leaking into the passenger compartment. The heater core can have a leak or it can be plugged.
Leak. What kind of liquid should be coming out? Antifreeze? Oil? And would it make the overflow for the raditor liquid bubble?
A broken fan heater can not work and A FORD Foucs does not run
No heat when you turn it on in the car.
Low coolant? Thermostat not opening? Plugged or restricted heater core? Heater core airbound? Heater valve control cable detached or broken?
Broken or split hose Radiator leak heater core leak
The heater core or connecting hose is broken.
The most common signs of a heater core problem is either leaking antifreeze or a mist coming from the air vents. There will also be a sickly sweet smell in most cases.
the heater core in the heater unit may not have air going through it, or the hoses for the water to pass through the heater core may be broken. Or the flaps controlling the airflow may not be working correctly
If it's leaking coolant, then it's not a good idea to, unless you pinch off the lines to the heater core.
A temporary fix would be to pull both heater hoses and connect them to each other, then don't worry about the heater core leaking. It's summer in the northern hemisphere, and you don't NEED a heater.
With the vehicle warmed up and the heater on, grab and feel the two heater hoses. If only one is hot, you've got blockage either in the lines or in the heater core itself. If both are hot, the problem is going to be your blend door.