It is very distressing to turn on a passenger-compartment heater and receive only cold air. If there is no sound, it may mean that debris is jamming the fan or the blower motor doesn’t work and needs replacing. Otherwise, the problem may rest with an electrical fault such as a blown fuse, a bad relay switch or resistor, or a loose wire. A blown fuse is a symptom of an overloaded circuit, which requires some investigation to identify. If the blower motor works, but there is no air coming from the ducts, the problem may be a jammed or inoperative air flow control or blend door. Poor heater performance may also be due to a clogged cabin air filter.
TIP: When poor heater performance cannot be traced to a blower motor, the problem may rest with blocked coolant flow through the heater core, low coolant level, a defective thermostat, or a weak water pump.
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Please drive safely.