- 1). Set the blower fan and heater to the highest setting with the engine running to ensure air is blowing across the heater core. If you do not hear the fan turn on, a fuse may have blown, or the fan itself could have malfunctioned.
- 2). Check the fuse box (under driver's side dash) for any fuses that might have blown. Read the instruction schematic on the inside of the fuse box cover for how to locate the fuse corresponding to the heating system. If the thin metal strip inside the glass fuse tube is broken or damaged, replace it with another of the exact same amperage rating.
- 3). Feel the carpet on the passenger side for any wetness. If it is damp, with a strong, sweet odor, this could indicate coolant leaking from the heater core. Have a qualified mechanic investigate further for you, as the heater core may need replacement.
- 4). Ensure that there is sufficient coolant in the radiator. The heater uses a small amount of coolant to heat the vehicle. When the level is too low, air can get trapped in the system and block the flow of heated air into the vehicle. Start the engine and open the hood. Feel the two heater hoses protruding from the firewall. The firewall is the thin metal partition between the passenger and engine compartments. Both hoses should be hot to the touch. If they are not, the flow of coolant could be blocked. The heater core may need replacement.
- 5). Check to see if the thermostat is stuck open. Crank the engine when it is cold. Open the hood and place your hand on the upper radiator hose to see if you feel coolant flowing through it. If you do, this could mean that the thermostat is stuck open as it only normally begins to flow when the engine warms up. Have a qualified mechanic investigate this further for you.