a thermal over load switch
Perhaps a bad thermostat and/or a heater core
faulty control valve on heater or air in the lines
no , the heater core provides heat to the interior for the passengers
If you have lost a sufficient amount of coolant this will stop the heater working because there will be no hot water in the heater rad.
By overheating which will cause a change in the thermostat materials construction.
thermostat stuck
Laika of Sputnik II died due to overheating as a result of a malfunctioning heater in her capsule.
It is an electric heater, with the heating elements in a straight line (a strip)
There are several reasons why this might occur. If your fluid level is low, your engine will not circulate enough antifreeze to fill your heater core ( which usually leads to your engine overheating, but not always if you are just borderline low), if your heater core is plugged (most common) or if you have a sealed system and there is air in the system which prevents your liquidfrom running through the heater core. The most likely cause is a bad heater core which is bad news because it is hard to access, therefor hard to replace.
Low coolant. If the coolant is low then the heater core is not able to transfer heat in to the car.
Check for a line leak to your heater core or a leak in the heater core it self. Usually it is under the dash on passinger side.
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