The main symptom of a failed heater core in a car is a lack of heat from the heater or defroster. More condensation than usual on the windshield and damp floor mats can signify a blocked core. Orange or green drips from under the instrument panel indicate leaks.
The heater core is typically located inside the dashboard on the passenger side of the vehicle. Because the core is difficult to access and messy to replace, car repair specialists recommend that the owner first inspect the coolant system hoses and connections for leaks. Low antifreeze levels in the radiator mimic heater core failure. If the coolant system is topped up and not leaking but there still isn't any heat, the core needs to be replaced.